4th ITG International Vacuum Electronics Workshop 2014 October 13 – 14, 2014, Physikzentrum Bad Honnef (www.pbh.de), Germany

Workshop, Previous Day

Sunday, October 12, 2014 15:30 ITG(VDE)-Fachausschuss 8.6 “Vakuumelektronik und Displays”,

124th Meeting Physikzentrum Bad Honnef (PBH), Sitzungszimmer: Wintergarten

18:30 Start of the ITG Workshop for all participants: Come Together Dinner & Evening Discussion, Physikzentrum Bad Honnef: Lichtenberg-Keller (at basement level)

Workshop Program, 1st Day

Monday, October 13, 2014 Location: Wilhelm und Else Heraeus Hörsaal

08:30 Welcome Address: Wolfram Knapp, Workshop Chairman

08:40 L1.1-1

09:05 L1.1-2

09:30 L1.1-3

09:55 L1.1-4

Session 1.1: Vacuum Measurements and Vacuum Electronics in Plasma Applications Chairman: Wolfram Knapp

PROGRESS IN VACUUM PRESSURE MEASUREMENT Martin Wüest1

1INFICON Ltd, Alte Landstr. 6, LI-9496 Balzers, Liechtenstein

REDUCTION OF GAS-SPECIES DEPENDENCY OF VACUUM GAUGE SYSTEMS BY AN AUTOMATED SOFTWARE CALIBRATION PROCEDURE Florian Dams1, Rupert Schreiner1

1OTH Regensburg, Seybothstr. 2, D-93053 Regensburg, Germany

INVESTIGATIONS ON APPLICATION POTENTIAL OF PULSED ELECTRON BEAM DEPOSITION Sebastian Schmidt1, Benjamin Graffel1, Falk Winckler1, Björn Meyer1, Gösta Mattausch1, Frank-Holm Rögner1

1Fraunhofer Institute for Electron Beam and Plasma Technology FEP, Winterbergstr. 28, D-01277 Dresden, Germany

HIGH TEMPERATURE FURNACE AND PLASMA CHAMBER REACTION MONITORING USING INFICON CPM RESIDUAL GAS ANALYZER Kenneth Wright1, Phillip Mach2, Guido F. Verbeck2

1INFICON Inc., 2 Technology Pl., East Syracuse, NY 13057, USA, 2Dept. of Chemistry, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA

10:20 Coffee Break

10:50 L1.2-1

11:15 L1.2-2

11:40 L1.2-3

12:05 L1.2-4

Session 1.2: Field Emission Cathodes and Applications (I) Chairman: Hans W. P. Koops

CHARACTERIZATION AND PROPERTIES OF PLANAR FIELD EMISSION CATHODES Oliver Gröning1

1Swiss Federal Laboratories of Material Testing and Research, Empa, CH-8600 Dübendorf, Switzerland

SPECTROSCOPY OF PULSED LASER EXITED AND FIELD EXTRACTED ELECTRONS S. Mingels1, V. Porshyn1, G. Müller1

1FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany

SUITABILITY OF CARBON-BASED NANOSTRUCTURES FOR VARIOUS COLD CATHODE APPLICATIONS Pavel Serbun1, Günter Müller1

1FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany

FABRICATION, SIMULATION AND CHARACTERIZATION OF HIGH ASPECT RATIO SILICON TIP CATHODES Christoph Langer1, Robert Lawrowski1, Christian Prommesberger1, Florian Dams1, Pavel Serbun2, Michael Bachmann3, Günter Müller2, Rupert Schreiner1

1OTH Regensburg, Seybothstr. 2, D-93053 Regensburg, Germany, 2FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany, 3Ketek GmbH, Hofer Str. 3, D-89737 München, Germany

12:30 Lunch

13:30 L1.3-1

13:55 L1.3-2

14:20 L1.3-3

Session 1.3: X-Ray Tubes and Gyrotrons (I) Chairman: Günter Kornfeld

BUNCHED ELECTRON EMISSION FROM GRAPHENE EMITTERS WITH GaAs PHOTOSWITCH O. Yilmazoglu1, S. Al-Daffaie1, F. Küppers1, H. L. Hartnagel1, Y. Neo2, H. Mimura2

1Technische Universität Darmstadt, D-64283 Darmstadt, Germany, 2Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan

FIELD EMISSION INITIATED GLOW DISCHARGE WITH LONG PULSES AND HIGH CURRENTS Daniela Wenger1,3, Wolfram Knapp2, Bernhard Hensel3, Sandro F. Tedde1

1Siemens AG, Corporate Technology, D-91058 Erlangen, Germany, 2IFQ, Otto von Guericke University of Magdeburg, D-39106 Magdeburg, Germany, 3MSBT, University of Erlangen-Nuremberg, D-91054 Erlangen, Germany

STATUS AND PROSPECTS OF GYROTRON DEVELOPMENT AT KIT: 2014 UPDATE J. Jelonnek1,2, K. A. Avramidis1, J. Franck1, G. Gantenbein1, K. Hesch3, S. Illy1, J. Jin1, P.

14:45 L1.3-4

Kalaria1, A. Malygin1, I. Gr. Pagonakis1, T. Rzesnicki1, S. Ruess1,2, A. Samartsev1, A. Schlaich1, T. Scherer4, D. Strauss4, M. Thumm1,2, C. Wu1, J. Zhang1

Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany, 1IHM, 2IHE, 3KIT Nuclear Fusion, 4IAM-AWP

DESIGN ASPECTS FOR DEMO-COMPATIBLE 2 MW GYROTRONS: ELECTRON GUN AND CAVITY J. Franck1, K. A. Avramidis1, S. Illy1, J. Jelonnek1, I. Gr. Pagonakis1, M. Thumm1

1

Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany

15:10 Coffee Break

15:40 L1.4-1

16:05 L1.4-2

16:30 L1.4-3

16:55 L1.4-4

Session 1.4: Gyrotrons (II) Chairman: Ernst Bosch

CONVENTIONAL CYLINDRICAL-CAVITY GYROTRON DESIGN FOR DEMO P. Kalaria1, K. A. Avramidis1, J. Franck1, S. Illy1, J. Jelonnek1, I. G. Pagonakis1, M. Thumm1 1

Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany

SECONDARY ELECTRON EMISSION MODEL IN THE CODE ESRAY&ESPIC J. Zhang1, S. Illy1, I. Gr. Pagonakis1, J. Jelonnek1, M. Thumm1

1Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany

DEVELOPMENT AND OPTIMIZATION OF AN INVERSE MAGNETRON INJECTION GUN FOR FUTURE FUSION GYROTRONS S. Ruess1,2, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2, I. Gr. Pagonakis1, T. RzesnickiKarlsruhe Inst. of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany,

1

1Institute for Pulsed Power and Microwave Technology (IHM) 2

Institute of High Frequency Techniques and Electronics (IHE)

INITIAL STEPS TOWARDS MULTI-STAGE COLLECTORS FOR GYROTRONS Chuanren Wu1, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2, I. Gr. Pagonakis1, M. ThummKarlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany

1,2

1Institute for Pulsed Power and Microwave Technology (IHM) 2

Institute of High Frequency Techniques and Electronics (IHE)

18:30 Workshop Dinner & Evening Discussion

Physikzentrum Bad Honnef: Lichtenberg-Keller (at basement level)

Workshop Program, 2nd Day Tuesday, October 14, 2014 Location: Wilhelm und Else Heraeus Hörsaal

08:40 L2.1-1

09:05 L2.1-2

09:30 L2.1-3

09:55 L2.1-4

Session 2.1: Vacuum Interrupters and Pulsed Power Switching Chairman: Gösta Mattausch

COMBINED EXPERIMENTAL AND THEORETICAL STUDY OF CONSTRICTION THRESHOLD OF LARGE-GAP AMF VACUUM ARCS N. Wenzel1, A. Lawall2, U. Schümann2, S. Wethekam3

Siemens AG, Germany 1Corporate Technology, Günther-Scharowsky-Str. 1, D- 91058 Erlangen, 2 Infrastructure & Cities, Low & Medium Voltage Division, Rohrdamm 88, D-13629 Berlin, 3

Energy Sector, Power Transmission Division, Nonnendammallee 104, D-13629 Berlin

NEW ULTRA FAST EARTHING SWITCH (UFES) DEVICE BASED ON VACUUM SWITCHING PRINCIPLE Dietmar Gentsch1

1

D-40472 Ratingen, Germany ABB AG, Calor Emag Medium Voltage Products, Oberhausener Str. 33,

DIELECTRIC TESTING OF HV VACUUM INTERRUPTERS DURING CAPACITIVE CURRENT SWITCHING B. Baum1, H. Janssen1, V. Hinrichsen1 1Technische Universität Darmstadt, High Voltage Laboratories, D-64283 Darmstadt, Ger.

TRIGGERED SPARK GAP WITH INTERNAL TRIGGER DELAY CIRCUIT Wolfgang Däumer1, Peter Bobert1, Frank Werner1

1EPCOS AG, A TDK Group Company, Rohrdamm 88, D-13629 Berlin, Germany

10:20 Coffee Break

10:50 L2.2-1

11:15 L2.2-2

Session 2.2: Fundamentals in Vacuum Electronics, HEMP Thrusters and Klystrons Chairman: Andreas Lawall

GIANT CURRENT DENSITY IN KOOPS-GRANMAT - IS IT DUE TO A BEC CONDENSATE AT ROOM TEMPERATURE? Hans W. P. Koops1

1HaWilKo GmbH, Ober-Ramstadt Germany

SELF-SCREENING EFFECT OF INDIVIDUAL CNT FIELD EMITTER WITH HIGH ASPECT RATIO Wolfram Knapp1

1IFQ, Otto von Guericke University of Magdeburg, D-39106 Magdeburg, Germany

11:40 L2.2-3

12:05 L2.2-4

A FULLY KINETIC AND SELF-CONSISTENT SIMULATION OF A HEMP-THRUSTER USING A STATISTICAL APPROACH FOR SOLVING THE “ANOMALOUS ELECTRON TRANSPORT” PROBLEM Günter Kornfeld1 1 Kornfeld Plasma & Microwave Consulting, D-89275 Elchingen, Germany

X-BAND HOLLOW-BEAM KLYSTRON DESIGN WITH CORKSCREW-MODULATION Jiwei Nie1, Heino Henke1, André Grede2

1Technische Universität Berlin, Sekr. EN-2, Einsteinufer 17, D-10587 Berlin, Germany, 2Hüttinger Elektronik, Boetzinger Str. 80, D-79111 Freiburg, Germany

12:30 Lunch

13:00 L2.3-1

13:25 L2.3-2

13:50 L2.3-3

14:15 L2.3-4

14:40 L2.3-5

15:05

Session 2.3: Traveling Wave Tubes (TWTs) Chairman: Manfred Thumm

BROADBAND TRAVELING WAVE TUBES IN Ka- GRANTS MODERN COMMUNICATION E. Bosch1, A. Laurent1, P.Ehret1, Jean Gastaud1

1THALES Electron Devices, 78141 Vélizy, France, and D-89077 Ulm, Germany

THALES 150 W C-BAND TRAVELLING WAVE TUBES W. Dürr1, C. Dürr1, P. Ehret1, E. Bosch1

Thales Electronic Systems GmbH, Söflinger Str. 100, D-89077 Ulm, Germany

BEAD-PULL MEASUREMENT OF A W-BAND FOLDED WAVEGUIDE STRUCTURE Heinrich Büssing1, André Grede2, Heino Henke1

1Technische Universitat Berlin, Sekr. EN-2, Einsteinufer 17, D-10587 Berlin, Germany, 2Hüttinger Elektronik, Boetzinger Str. 80, D-79111 Freiburg, Germany

SIMULATION OF BEAM-WAVE INTERACTION IN FILTER-TYPE SLOW WAVE STRUCTURES OF TRAVELLING WAVE TUBES Philip Birtel1, Elke Gehrmann2, Sascha Meyne2, Arne F. Jacob2

1Thales Electron Devices, Söflinger Str. 100, D-89077 Ulm, Germany, 2Technische Universität Hamburg-Harburg, Institut f. Hochfrequenztechnik, D-21073 Hamburg, Germany,

HOT MATCHING ANALYSIS OF A GENERIC TWO-SECTION COUPLED-CAVITY TRAVELING-WAVE TUBE Sascha Meyne1, Jean-François David2, Arne F. Jacob1

1 Institut für Hochfrequenztechnik, Technische Universität Hamburg-Harburg, Hamburg, Germany, 2 Thales Electron Devices, Vélizy, France

Closing Words: Manfred Thumm, Workshop Co-Chairman

15:15

Coffee Break → End of Workshop: 16:00

PROGRESS IN VACUUM PRESSURE MEASUREMENT

Martin Wüest1 1INFICON Ltd, Alte Landstrasse 6, LI-9496 Balzers, Liechtenstein

ABSTRACT

For many years standard vacuum pressure measurement sensors consist of capacitance diaphragm gauges, Pirani heat transfer gauges as well as ionization gauges. Development has progressed from passive gauges with a detached controller to combination gauges with integrated electronics. Market demand from the semiconductor industry continues to force the development of smaller, cheaper and better process sensors. Better in this context means the sensors must survive the harsh process conditions for longer, measure faster and with better reproducibility. I will present some of the recent developments.

Reduction of Gas-Species Dependency of Vacuum Gauge Systems by an Automated Software Calibration Procedure

Florian Dams1, Rupert Schreiner1

1OTH Regensburg, Seybothstrasse 2, D-93053 Regensburg, Germany

Topic: A3 Vacuum Microelectronic and Nanoelectronic DevicesPreferred Presentation Form: P Poster Presentation

ABSTRACT

For vacuum pressure measurement different measurement principles are necessary due to the large range of the pressure regime of several orders of magnitude. In rough vacuum pressure can be measured independent of the species of the residual gas by membrane gauges. Gauges with measurement principles that are well suited for lower pressure regimes produce a signal that also depends on the gas species. Such gauges like thermal conductivity (“Pirani”) or ionization vacuum gauges are calibrated for nitrogen and the pressure value has to be corrected by gauge specific calibration curves of the used gas [1, 2].

In common vacuum applications different gauges are used to cover a specified pressure region. If the signal of one gauge in the system is gas species independent it can be used to calibrate the other one in the overlap region of their measurement ranges [3]. By such a procedure the gas species dependency of the system is significantly reduced if the gas composition does not change below the calibration pressure [4].

In this work we present such an automated in-system calibration procedure with a system consisting of MEMS-based Pirani gauge [5] as gas species dependent sensor and a gas species independent membrane gauge. The dependence of the characteristic curve on the gas type of the Pirani gauge can be described analytically. Furthermore due to the miniaturized geometry of the sensor there is a significant overlap of the measurement region with that one of gas species independent gauge. During pumping down the calibration curve of the Pirani vacuum gauge is calculated by a microcontroller based on the signal of the membrane gauge. Afterwards the fit parameter of this curve are used for calibration of the thermal conductivity vacuum gauge. By this way the gas species dependency of the system was significantly reduced.

References

[1] K. JOUSTEN, J. Vac. Sci. Technol. A 26, 352 (2008).[2] R.E. ELLEFSON and A.P. MIILLER, J. Vac. Sci. Technol. A 18, 2568 (2000).[3] H. PLÖCHINGER, Patent DE19860500 A1 (2000)[4] F. DAMS and R. SCHREINER, in Proceedings of the 8th International Conference & Exhibition on Integration Issues of Miniaturized Systems, Vienna, April 2014, edited by T. Gessner (Apprimus, Aachen, 2014) p. 459.[5] F. DAMS and R. SCHREINER, J. Vac. Sci. Technol. A 32, 031603 (2014).

Investigations on application potential of Pulsed Electron Beam Deposition Sebastian Schmidt1, Benjamin Graffel1, Falk Winckler1, Björn Meyer1,

Gösta Mattausch1, Frank-Holm Rögner1 1Fraunhofer Institute for Electron Beam and Plasma Technology FEP

Winterbergstraße 28, 01277 Dresden, Germany

ABSTRACT This paper presents the Pulsed Electron Beam Deposition (PED) process, a new field of work at FEP. This was enabled by a special electron beam source recently developed and delivered by Organic Spintronics srl. Its function principle relies on a channel-spark discharge. The source generates a short-pulsed, polyenergetic electron beam with a very high power density (≥ 108 W/cm² over some nanoseconds). When directed to a target, the surface of the material is locally heated to an extent that ablation occurs, with subsequent propagation of the vapour towards the substrate in a directional flow [1]. As opposed to classic EB-PVD (Electron Beam Physical Vapour Deposition), the source material to be evaporated remains solid in PED. The advantage is that this allows for homogeneously depositing alloys in the proper stoichiometric ratio, because there is no accumulation of the less-volatile components due to the avoidance of a molten bath. Furthermore, the coating rate can be precisely adjusted facilitated by defined energy pulses. When compared to alternative Pulsed Laser Deposition (PLD), PED excels by lower system costs in case of industrial application. An essential feature of the PED process includes its high variability: nearly all materials (both electrically conductive and insulating materials) may be ablated, and the energy utilization efficiency is high. The undesired deposition of micro-particles (“droplets”) during layer formation can be suppressed by optimizing the process parameters. Beneficial particularities of PED include the formation of dense discharge plasma. It increases the energy of the ablated particles to some 10 eV at a degree of ionization of vapour particles of 30…70 % and thus to a higher energy level than reached during EB-PVD or sputtering, for example. This positively influences the properties of the growing layers so that the substrate temperature can be kept low. Therefore, the growing of well-adhering, dense layers is also made possible on temperature-sensitive substrate materials – such as p lastics. Moreover, reactive process control is possible by adding the corresponding gases. As a result, there are numerous different application possibilities like the production of hard material layers, decorative layers, or transparent, conductive oxide layers. Further potential applications can be found in the field of flexible displays and in the domain of heterostructured thermoelectric materials. The first tests of the new source at FEP were intended to develop a general understanding of the PED process, as well as to investigate the suitability of the method for different applications. For instance, the deposition of thin metal and semiconductor layers was examined in process chains for photovoltaic applications. Furthermore, promising trials regarding the deposition of transparent conductive oxide layers as well as i nsulating layers were conducted. References [1] G. MUELLER, M. KONIJNENBERG, G. KRAFFT, and C. SCHULTHEISS. Thin Film Deposition by Means of Pulsed Electron Beam Ablation. in: F.C. MATACOTTA and G. OTTAVIANI (eds). Science and Technology of Thin Films. World Scientific Publishing Co. Pte. Ltd., 1995, pp. 89-119 Preferred form of presentation: O

High Temperature Furnace and Plasma Chamber Reaction Monitoring Using INFICON CPM

Residual Gas Analyzer

Kenneth Wright1, Phillip Mach2, and Guido F. Verbeck2

1INFCION Inc., East Syracuse, NY USA 2 Dept. of Chemistry, University of North Texas, Denton, TX USA

ABSTRACT

Residual gas analyzers continue to be of value in monitoring semiconductor manufacture and other process treatments. Extending this technology and the ability of INFICON’s RGA based Compact Process Monitor (CPM) to provide meaningful data in measuring gas phase reactions, recognizing trace level analyte contaminants, and qualifying gas purity to plasma chamber reactions and in high temperature furnaces in situ has proved the effectiveness of using this instrumentation beyond process monitoring. Experiments observing the carbothermal reduction mechanisms of Yttria-Stabilized Zirconia (YSZ) have yielded insights into determining whether carbon dioxide (CO) is the driving force behind conversion of ZrO2 to ZrC. The reaction products were analyzed in real time, in conjunction with temperature program data, to provide insight into reaction mechanisms. Furthermore, the CPM was used in monitoring plasma process reactions. Gas analysis of downstream plasma effluent yields insight into plasma precursor dissociation and molecule species creation. The use of the CPM in observing plasma treatment of carbon nanotubes and post reaction effluent gases from them has provided insight into new nanotube gas absorbing mechanisms. The extension from process monitoring to observing plasma and high temperature reactions is a novel step forward in using the CPM, ultimately this will provide new insights into various progressive techniques. The design, performance, and recent advances towards the next generation CPM will also be discussed.

Characterization and Properties of Planar Field Emission Cathodes Oliver Gröning nanotech@surfaces Laboratory Swiss Federal Laboratories for Materials Testing and Research, Empa CH-8600 Dübendorf oliver.groening@empa.ch Abstract The emission of electrons into vacuum by electric field induced tunneling is an elegant way to produce beams of free electrons for various applications in imaging, displays, analytics or X-Ray generation. The drawback of field emission is the circumstance, that the required electric fields above 1 GV/m cannot be created in a controlled and reliable manner on a flat surface. Instead the field enhancing effect of tip like metallic structures must be exploited to locally generate the extraction field, which however reduces the actual emitting surface drastically and therefore also the emitted current. A way out of this problem is to use planer emitter arrays, where the emission current of a device originates from multiple emission sites, where the emission current is scaled by the density of emission sites. This approach has been pushed particularly in the context of the development of field emission displays, where homogenous, large area electron emission is at the heart of the device operation. In was also this context that shortcomings in the characterization of field emission using simple diode setups have become apparent. In this presentation we will discuss the particular difficulties of a meaning full characterization of planar field emission cathodes and how these difficulties can be overcome using a local scanning probe. The basic layout of the scanning anode field emission microscope (SAFEM) will be presented and how this instrument can be used to acquire statistical evaluations of the emission sites and their individual field emission properties on a planar field emission cathode (e.g. a carbon nanotube cathode). As an example we will show and quantify experimentally and theoretically ensemble effects like electrostatic shielding. We will then discuss how such data can be used to develop a macroscopic emission model of the cathode and understand effects like degradation and emission current limitation. Based on this discussion we will examine different strategies for the improvement of field emission cathodes.

SPECTROSCOPY OF PULSED LASER EXITED AND FIELD EXTRACTED ELECTRONS

S. Mingels, V. Porshyn, G. MüllerFB C Department of Physics, University of Wuppertal, Wuppertal, Germany

Topic: Electron Sources and Electron Emission

ABSTRACT

In order to develop highly brilliant, pulsed electron sources based on photo-induced field emission(PFE), which combines advantages of photo and field emission FE, a new measurement system was constructed at BUW*. It can provide direct as well as indirect spectroscopy of electrons from cold cathodes in a triode configuration under high electric fields (up to ~100 MV/m) by a recently installed hemispherical spectrometer (resolution = 6.7 meV) and quantum efficiency QE measurements under pulsed tuneable laser illumination (3.5 ns, 10 Hz, 0.5-5.9 eV, > 0.3 mJ), respectively. Moreover, a comprehensive system upgrade was performed, which enables precise triode positioning, controlled sample cooling or heating (77-400 K), and dust protected sample insertion. First tests of the apparatus and the spectrometer commissioning were carried out with DC FE from a W tip resulting in a reliable work function of 4.42 ± 0.19 eV compared to the literature value of 4.55 eV**. Further measurements of pulsed spectra from flat PFE cathodes are planned and will be presented at the workshop.

* B. Bornmann et al., Rev. Sci. Instrum. 83, 013302 (2012)** B.J. Hopkins and J.C. Rivière, Proc. Phys. Soc. 81, 590 (1963)

Suitability of carbon-based nanostructures for various cold cathode applications

P. Serbun*, G. Müller

FB C Physics Department, University of Wuppertal, Wuppertal, Germany

Field emission (FE) cathodes are considered as attractive alternative to thermionic or photo cathodes for the generation of high-current, low-emittance and ns-pulsed electron beams. Bottom-up grown nanostructures like carbon nanotubes (CNT) and carbon nanowalls (CNW) provide excellent electron field-emission (FE) properties due to their high aspect ratio. Therefore, such cathodes have been optimized for a variety of vacuum device applications, e.g. flat light sources, compact X-ray tubes and microwave amplifiers [1, 2, 3].

Nevertheless, actual CNT and CNW FE cathodes have some disadvantages that need to be overcome in order to fully exploit their application potential. CNT suffer from poor contact to the substrate, which result in high contact resistance, limited FE current and lifetime [4, 5]. Furthermore, the varying shape, random alignment and mutual shielding of CNT and CNW often limit the homogeneity of such FE cathodes [6, 7] and cause low transmission efficiency of triode structures.

Therefore, different approaches to improve the FE homogeneity, current density and contact interface of structured carbon-based cathodes for diode and triode applications will be presented and discussed at the workshop.

[1] J. Eichmeier, M. Thumm (Eds.), “Vacuum electronics: components and devices”, Springer-Verlag Berlin Heidelberg (2008).

[2] Y. Saito, “Carbon Nanotubes and Related Field Emitters”, Wiley-VCH, Weinheim (2010).

[3] A. N. Obraztsov, V.I. Kleshch, and E.A. Smolnikova, Beilstein J. Nanotechnol. 4, 493 (2013).

[4] L. Nilson, O. Gröning, P. Gröning, and L. Schlapbach, App. Phys. Lett. 79, 1036 (2001). [5] S. Purcell, P. Vincent, C. Journet, and V. Binh, Phys. Rev. Lett., 88, 105502 (2002). [6] A. Navitski, G. Müller, V. Sakharuk, A.L. Prudnikava, B.G. Shulitski and V.A. Labunov,

J. Vac. Sci. Technol. B 28, C2B14-19 (2010). [7] A. Navitski, P. Serbun, G. Müller, R.K. Joshi, J. Engstler, and J.J. Schneider, Eur. Phys.

J. Appl. Phys. 59, 11302/1-6 (2012). Area: Vacuum Electronic and Discharge Devices and their Applications Topic: A3 Vacuum Microelectronic and Nanoelectronic Devices Preferred Presentation Form: Talk

Fabrication, Simulation, and Characterization of High Aspect Ratio Silicon Tip Cathodes

Christoph Langer1, Robert Lawrowski1, Christian Prommesberger1, Florian Dams1, Pavel Serbun2, Michael Bachmann3, Günter Müller2 and Rupert Schreiner1

1OTH Regensburg, Seybothstraße 2, D-93053 Regensburg, Germany 2University of Wuppertal, Gaußstraße 20, D-42097 Wuppertal, Germany

3Ketek GmbH, Hofer Straße 3, D-81737 München, Germany

Topic: A3 Vacuum Microelectronic and Nanoelectronic Devices Preferred Presentation Form: P Poster Presentation

ABSTRACT Silicon field emission (FE) cathodes are promising candidates for the application in electron sources, vacuum sensors and x-ray tubes. As presented in [1, 2] it is possible to fabricate very homogeneous n-type, p-type, and metal coated silicon tip arrays with a field enhancement factor in the range of 60 to 140. Based on these results, we improved our fabrication process using a combination of reactive-ion-etching (RIE) and subsequent etching with an inductively-coupled-plasma (ICP). That additional step allows us to realize sharp tip structures on top of elongated pillars. By simulations with COMSOL Multiphysics® the geometric field enhancement factor β was calculated. Therefore, the elliptic curvature shape model given in [3] was adapted to the new geometry of the emitters. N-type as well as p-type silicon structures with a total height of ≈5 µm, a pillar height of ≈4.5 µm, a pillar diameter of ≈1 µm, an aperture angle of ≈60°, and an apex radius less than 20 nm were fabricated. These FE cathodes were characterized by field emission scanning microscopy [4] under ultra-high vacuum conditions. Integral measurements of arrays with 271 tips showed low onset-fields of ≈10 V/µm and field enhancement factors of up to 700 during up- and down-cycle. With n-type silicon structures the expected FN-behaviour was observed, whereas p-type silicon structures showed saturation region above ≈15 V/µm. Compared to our previously fabricated Si-tip structures [1, 2] the saturation region is more pronounced. The saturation behaviour can be explained by the limited number of electrons in the conduction band [5] and a further carrier depletion effect caused by the pillars themselves [6]. At an operating point in the saturation region a fluctuation of the emission current below ±2% was observed with p-type silicon tips on pillars. That combination offers an excellent method to stabilize the emission current. References [1] F. DAMS, A. NAVITSKI, C. PROMMESBERGER, P. SERBUN, C. LANGER, G. MÜLLER, R. SCHREINER, IEEE Trans. Electron Devices, vol. 59, pp. 2832–2837, 2012. [2] P. SERBUN, B. BORNMANN, A. NAVITSKI, G. MÜLLER, C. PROMMESBERGER, C. LANGER, F. DAMS, R. SCHREINER, J. Vac. Sci. Technol. B, vol. 31, pp. 02B101, 2013. [3] C. LANGER, C. PROMMESBERGER, F. DAMS, R. SCHREINER, Proc. of IVNC 2012, pp. 148–149, 2012. [4] D. LYSENKOV, G. MÜLLER, International Journal of Nanotechnology, vol. 2, pp. 239, 2005. [5] D. K. SCHRODER, R. N. THOMAS, J. VINE, H. C. NATHANSON, IEEE Trans. Electron Devices, vol. 21, pp. 785–798, 1974. [6] L. F. VELASQUEZ-GARCIA, S. A. GUERRERA, Y. NIU, A. I. AKINWANDE, IEEE Trans. Electron Devices, vol. 58, pp. 1775–1782, 2011.

Bunched electron emission from graphene emitters with GaAs photoswitch

O. Yilmazoglu1*, S. Al-Daffaie1, F. Küppers1, H. L. Hartnagel1, Y. Neo2, H. Mimura2 1Technische Universität Darmstadt, 64283 Darmstadt, Germany.

2Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan. *yilmazoglu@hfe.tu-darmstadt.de

ABSTRACT A simple photocathode for bunched electron emission was fabricated and used for field electron emission in a diode configuration. Commercial graphene nanoplatelets were used as field emitter array with low turn-on field. The graphene nanoplatelets have thicknesses in the range of 2-10 nm and a high aspect ratio of 1000-2000. A low turn-on electric field of ~1.5 V/µm (defined at 1µA/cm2) was obtained for this emitter. The photo-modulation was achieved with a GaAs photoswitch in series to the bottom of the graphene emitters. The semi-insulating (s.i.) GaAs is a promising high-power and fast photoswitch with high electron mobility (>6000 cm2/Vs), sub-nanosecond carrier lifetime [1] and high quantum efficiencies. A single photoconductive GaAs switch in a planar configuration can handle currents and voltages as high as 3.7 kA and 28 kV, respectively [2]. Furthermore, the s.i. GaAs has a high resistivity of > 1 x 107 Ωcm and a high electric breakdown field of >2x104 V/cm. A simple low-power low-cost external laser modulated the GaAs photoswitch. This photocathode configuration can find applications in optically driven X-ray sources with high on/off ratio for X-ray imaging. Initial field emission measurements showed an on/off ratio > 200 and modulation up t o 300 kHz (Fig.1). New photoswitches with very low carrier life-time can open further promising applications in high-charge short-pulse electron sources to produce fast electron bunches for x-ray free electron lasers as well as for miniaturized high frequency vacuum tubes. The dc characteristics as well as fast photo-modulated field emission currents will be presented. Furthermore, a future design optimization for contact pulsed X-ray sources will be presented.

Fig. 1 Photo-modulated field emission current from graphene with GaAs photoswitch.

References [1] J. S. Weiner and P. Y. Yu, J. Appl. Phys. 55 (1984) 3889. [2] W. Shi et al., Appl. Phys. Lett. 92 (2008) 043511.

Field Emission Initiated Glow Discharge with Long Pulses and High Currents

D. Wenger1,3, W. Knapp2, B. Hensel3, S. F. Tedde1

1Siemens AG, Corporate Technology, 91058 Erlangen, Germany 2 IFQ, University of Magdeburg, 39106 Magdeburg, Germany

3 MSBT, University of Erlangen-Nuremberg, 91054 Erlangen, Germany

ABSTRACT

Field emitters are a promising alternative for thermionic electron sources in X-ray tubes. However the main challenges remain the achievement of stable and high field emission currents of more than 100 mA, even up to 1,5 A, with simultaneous current densities beyond 3 A/cm2. Field emission (FE) properties of SWCNT/graphene hybrid samples were investigated in DC as well as in pulsed mode. A transition of electron field emission to glow discharge was measured for high currents, long pulse-on times or high duty cycles with stainless steel anodes. Pulse-on times varied between 0.2 ms and 400 ms and duty cycles between 1% and 80%. DC measurements showed a slow transition to glow discharge already at currents greater than 10 mA. The pulsed IV-characteristics with up to 400 mA maximum current deviated also from the Fowler-Nordheim (FN) behavior. Constant-voltage behaviour arises after subtracting the cathode resistance. This constant voltage behavior, the observed glowing during field emission and time resolved measurements give evidence for the transition from FN type field emission to FE enhanced glow discharge. FE enables a soft transition to normal glow discharge without the need of an ignition voltage. The build-up dynamic and the respective time constants of the glow discharge will be evaluated and discussed, based on the observed data. Respective equivalent electric circuits for the FN-type field emission and for the normal glow discharge will be presented. Electron stimulated desorption (ESD) of stainless steel appears to be the most reasonable reason for this transition causing a pressure increase in the gap between cathode and anode in the range that glow discharge can be ignited. It was observed that almost no glow discharge occurs with copper or molybdenum anodes. The outgassing of stainless steel is significantly higher due to the low thermal conductivity and the high amount of ESD. References [1] D. Wenger, W. Knapp, B. Hensel, and S. F. Tedde, “Transition of Electron Field Emission to Normal Glow Discharge”, submitted 2014. [2] O. Malyshev, C. Naran, “Electron stimulated desorption from stainless steel at temperatures

between 15 and +70 C”, Vacuum 86, 1363 (2012).

STATUS AND PROSPECTS OF GYROTRON DEVELOPMENT AT KIT: 2014 UPDATE

J. Jelonnek1,2, K. A. Avramidis1, J. Franck1, G. Gantenbein1, K. Hesch3, S. Illy1, J. Jin1, P. Kalaria1, A. Malygin1, I. Gr. Pagonakis1, T. Rzesnicki1, S. Ruess1,2, A. Samartsev1, A. Schlaich1, T. Scherer4,

D. Strauss4, M. Thumm1,2, C. Wu1, J. Zhang1 Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany

1IHM, 2IHE, 3KIT Nuclear Fusion, 4IAM-AWP

ABSTRACT KIT is performing gyrotron research and development for the two major plasma fusion devices under construction in Europe, the stellarator Wendelstein 7-X (W7-X) at Greifswald, Germany [1] and the international experimental nuclear fusion reactor ITER at Cadarache, France [2]. As part of the European fusion development consortium (EUROfusion), KIT is contributing significantly to the development of gyrotrons which shall fulfil the future needs of DEMO, the nuclear fusion demonstration power plant that will follow ITER. Within that research and development, KIT is investing in the development of advanced design tools, in components research, and in a proper test environment. Both experiments, W7-X and ITER, are relying on electron cyclotron resonance heating (ECRH) as the main heating method for steady state operation, while it is planned for ITER to additionally apply electron cyclotron resonance technique for current drive (ECCD). Gyrotrons are the unique RF sources which meet the extraordinary requirements of those applications: RF output power in the MW range, operating frequencies up to 170 GHz, and pulse lengths of several seconds up to 1 h continuous wave operation (CW). Optimum current drive efficiencies for future nuclear fusion devices such as DEMO will require the development of gyrotrons operating at even higher frequencies (>200 GHz), offering efficiencies better than 60 % together with multi-MW levels of RF output power [3]. To prevent mechanical antenna steering close to the plasma, frequency step-tunable RF sources will be required for localized plasma stabilization [4]. KIT is contributing to this development by doing theoretical studies and experiments. In this presentation, the latest status and prospects of the different developments will be presented. Acknowledgement This work has been supported in parts by the European Community, under the contract of Association between EURATOM and Karlsruhe Institute of Technology (KIT) and within the framework of the European Fusion Development Agreement (EFDA), or under the EUROfusion consortium. Other parts have been supported by Fusion for Energy (F4E) under the contracts F4E-GRT-432 and F4E-OPE-458 to the European Gyrotron Consortium (EGYC). EGYC is a collaboration among CRPP, Switzerland; KIT, Germany; HELLAS, Greece; IFP-CNR, Italy. The views expressed in this publication do not necessarily reflect the views of F4E or the European Commission. References [1] V. Erckmann, et. al., Fusion Sci. & Techn. 52, 291, 2007, [2] C. Darbos, et. al., 35th IRMMW-THz, Rome, Italy, 2010 [3] H. Zohm, M. Thumm, J. of Physics: Conf. Series, 25, 274-282, 2005 [4] E. Poli, et. al., Nuclear Fusion, 53, no. 10, 2013

DESIGN ASPECTS FOR DEMO-COMPATIBLE 2 MW GYROTRONS:

ELECTRON GUN AND CAVITY

J. Franck, K. A. Avramidis, S. Illy, J. Jelonnek, I. Gr. Pagonakis, M. Thumm

Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of Technology (KIT),

Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen

ABSTRACT

In a commercial power plant based on magnetic confinement fusion of deuterium and tritium, especially

the first demonstration plant DEMO to be commissioned around 2050, the plasma needs to be heated up

to above 108 K in order to obtain a sufficient fusion rate. The required heating power of tens of

megawatts [1] and an effective plasma control can be provided by gyrotrons in the form of microwave

radiation via electron cyclotron resonance heating and current drive (ECRH&CD). Physical and

economic considerations demand high unit power, reliability and efficiency per tube at an output

frequency significantly above 200 GHz for both pulsed and steady-state operation according to current

studies [1].

In this talk, a design approach towards a coaxial-cavity 2 MW gyrotron will be presented. The approach

includes mode-selection based on multi-frequency operability as well as the design of the cavity and of

the coaxial triode-type magnetron injection gun. Critical design restrictions due to the quasi-optical

output system and to the window of the gyrotron are already addressed within the mode-selection

scheme. Thus, the gyrotron is optimized for mode TE49,29, corresponding to a frequency of 237.5 GHz,

but would also allow operation at other modes with sufficient efficiency, such as TE42,25 (at 203.8 GHz

for e.g. plasma control), TE35,21 (170.0 GHz) or TE56,33 (271.3 GHz for e.g. pulsed DEMO operation).

Results from numerical electron gun [2] and interaction simulations [3,4] will be presented.

Acknowledgment

This work, supported by the European Communities under the contract of Association between

EURATOM and Karlsruhe Institute of Technology, was carried out within the framework of the

European Fusion Development Agreement. The views and opinions expressed herein do not necessarily

reflect those of the European Commission.

References

[1] E. POLI et al 2013 Nucl. Fusion 53 013011

[2] I. GR. PAGONAKIS, J. L. VOMVORIDIS Proc. 29th

Joint Int. Conf. Infrared Millim. Waves, THz

Electron., Karlsruhe, Germany, 2004, pp. 657-658

[3] K. A. AVRAMIDES et al EPJ Web of Conferences 32, 04016 (2012)

[4] S. KERN wiss. Bericht des FZKA 5837, Karlsruhe 1997

CONVENTIONAL CYLINDRICAL-CAVITY GYROTRON DESIGN FOR DEMO

P. Kalaria, K. A. Avramidis, J. Franck, S. Illy, J. Jelonnek, I. Gr. Pagonakis, M. Thumm

Institute for Pulsed Power and Microwave Technology (IHM),

Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany

ABSTRACT

Based upon the experiences and results of the ITER experimental nuclear fusion reactor, a

demonstration power plant (DEMO) is proposed to be built to prove the technical and economic

feasibility of fusion energy. Electron Cyclotron Resonance Heating and Current Drive (ECRH&CD) of

the fusion plasma plays a key role in such a DEMO. The necessary mm-wave radiation is provided by

gyrotrons. To achieve sufficient fusion gain, it is desirable to use gyrotrons with frequencies around

240 GHz and electrical efficiencies higher than 60 %. Along with this, fast frequency tunability of

2-3 GHz and slow frequency tunability of 30 – 40 GHz (in a few seconds resp. minutes) is requested [1].

The use of broadband or step-tuneable single disk CVD diamond windows is proposed to achieve this

tuneability, while the beam interaction efficiency and the beam energy recovery system efficiency must

remain high to obtain the required efficiency. Along with conventional cavity gyrotrons, coaxial cavity

gyrotrons are being investigated at IHM, KIT to set the parameter space for the future gyrotron. The

design of the different gyrotron components (like interaction section, Magnetron Injection Gun (MIG),

Quasi-Optical Launcher (QOL) with the mirror box and multi-stage depressed collector (MDC)) is in

progress.

The following mode chain is suitable for the high-frequency, high-power conventional-cavity gyrotron

with good multi-frequency properties: TE19,7 (104 GHz) – TE25,9 (137 GHz) – TE31,11 (170 GHz) –

TE37,13 (203 GHz) – TE43,15 (236 GHz) – TE49,17 (267 GHz). At 236 GHz, the mode TE43,15 is selected

for optimization as cavity mode for the DEMO gyrotron. This vacuum tube would also support

170 GHz, TE31,11 mode operation for ITER and could be used for the ECCD system of a pulsed DEMO

version at 270 GHz. These modes possess the same caustic radius, thus the design of the QOL, mirrors

and the MIG fits for all these modes. The first three modes at 104 GHz, 137 GHz and 170 GHz have

been successfully operated by the JAEA gyrotron team [2].

The conventional cavity for the 236 GHz TE43,15 mode gyrotron is designed using the in-house

developed code package CAVITY. At high frequency (>200 GHz), the ohmic cavity wall loading is a

critical parameter for the cavity design. The physical parameters of the cavity are optimized such that

maximum output power and efficiency are achieved with the reasonable ohmic cavity wall loading of

2 kW/cm2. Single-mode and multi-mode self-consistent time-domain (SELFT) calculations predict

stable operation of the TE43,15 mode without serious competing modes for suitable start-up conditions.

The presentation will provide a comprehensive overview of the ongoing research which will lead to the

conventional-cavity gyrotron design for DEMO.

References

[1] M. Thumm, et al., in Proceedings of the 5th Int. Workshop on Far-Infrared Technologies (FIRT

2014), Fukui, Japan, 5-7 March 2014, p. 5-7.

[2] Y. Oda, K. Kajiwara, et al., EPJ Web Conferences 32, 04004, 2012.

Secondary electron emission model in the code ESRAY&ESPIC

J. Zhang, S. Illy, I. Gr. Pagonakis, J. Jelonnek and M. Thumm

Institute for Pulsed Power and Microwave Technology (IHM),

Karlsruhe Institute of Technology (KIT), Germany

In Magnetron Injection Guns (MIGs), secondary electrons are generated by the bombardment ofback reflected electrons on the cathode surface. These additional electrons from the cathode surfacehave higher probability to be trapped again by the magnetic mirror and the accumulation of trappedelectrons can cause Low Frequency Oscillation (LFO) and damage in the gyrotron.

A new secondary electron emission model based on the Furman secondary electron emission model[1] was developed for the code ESRAY&ESPIC. The Monte Carlo code CASINO [2] is used in orderto have more accurate angular distribution information of the elastic and re-diffused electrons. Therelation between the incident angle θ0 and the outward secondary electron angle θ and φ is shown inFig. 1.

(a) θ distribution (b) φ distributionFig.1 Angular distribution of the secondary electrons under different incident angle.

The secondary emission parameters for the two traditional cathode material tungsten andmolybdenum are deduced by fitting the existing experimental data [3].

The initial gun calculation results show that the secondary electrons will cause the accumulation oftrapped electrons, which could lead to LFO is observed in the gun region.

Acknowledgement:

This work, partially supported by the European Communities under the contract of Associationbetween EURATOM and KIT, was carried out within the framework of the European FusionDevelopment Agreement. The views and opinions expressed herein do not necessarily reflect those ofthe European Commission.

The authors are thankful to China Scholarship Council (CSC) for the financial support of this researchproject.

References:

[1] M. Furman and M. Pivi, “Probabilistic model for the simulation of secondary electron emission,”Physical Review Special Topics - Accelerators and Beams, vol. 5, p. 124404, Dec. 2002.

[2] H. Demers, N. Poirier-Demers, N. de Jonge, and D. Drouin, “Three-dimensional electronmicroscopy simulation with the casino monte carlo software,” Microscopy and Microanalysis,vol. 17, pp. 612–613, 7 2011.

[3] D. C. Joy, “A database on electron-solid interactions,” Scanning, vol. 17, no. 5, pp. 270–275,1995.

Development and Optimization of an Inverse Magnetron Injection Gun

for Future Fusion Gyrotrons

S. Ruess1,2

, K. A. Avramidis1, G. Gantenbein

1, S. Illy

1, J. Jelonnek

1,2, I. Gr. Pagonakis

1, T. Rzesnicki

1

Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany

1IHM,

2IHE

ABSTRACT

Electron Cyclotron resonance heating and current drive (ECRH&CD) is one of the major

plasma heating and stabilization techniques for nuclear fusion devices. The only source

which is capable to produce the high power microwaves for the ECRH&CD is the

gyrotron. It offers excellent coupling to the plasma and very good localization of the RF

power. The KIT is involved in three major projects: Wendelstein 7-X at IPP Greifswald,

ITER at Cadarache, France and future European DEMOnstration power plant (DEMO).

In order to minimize the necessary number of gyrotrons for future fusion power plants,

KIT is working on feasibility studies for multi-MW (>1 MW) gyrotrons. Additionally, to

achieve a sufficient current-drive efficiency, the operating frequency for future DEMO

gyrotrons will be above 200 GHz.

In this work an inverse Magnetron Injection Gun (MIG) was developed. A new type of

inverse electron gun preferable for the coaxial-cavity gyrotron, but also appropriate for

standard hollow-cavity gyrotrons is proposed. The geometry of the gun allows the design

of a significant larger emitter ring, hence significant larger current densities, using the

same size of bore hole for the super-conducting magnet (SCM) as for today’s gyrotrons.

Additionally, the geometry of the new type is significantly simpler when comparing to

the “conventional” gun. Trapped electrons in the gun region can be prevented much

easier in the design than before. In addition, this new type of gun could be used as a

triode gun without any geometrical modifications.

Acknowledgement

This work is supported by the European Community under the contract of Association

between EURATOM and Karlsruhe Institute of Technology (KIT). It is carried out

within the framework of the European Fusion Development Agreement (EFDA). The

views expressed in this publication do not necessarily reflect the views of F4E or the

European Commission.

INITIAL STEPS TOWARDS MULTI-STAGE COLLECTORS FOR GYROTRONS

Chuanren Wu, K. A. Avramidis1, G. Gantenbein

1, S. Illy

1, J. Jelonnek

1,2,

I. Gr. Pagonakis1, M. Thumm

1,2

Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany 1Institute for Pulsed Power and Microwave Technology (IHM)

2Institute of High Frequency Techniques and Electronics (IHE)

ABSTRACT

High-power gyrotrons are the unique sources for electron cyclotron resonance heating and current

drive (ECRH & CD) in plasma fusion devices. Gyrotrons for fusion experiments at the stellarator W7-

X and the tokamak ITER will operate at frequencies between 100 GHz and 200 GHz. The maximum

RF output power is up to 1 MW/2 MW at pulse lengths ranging from several seconds up to 1 h for

ITER. Today, the electronic efficiencies are typically <35 %. Therefore, always the concept of a

single-stage depressed collector (SDC) is used to recuperate some of the electron beam energy which

is not converted into RF power. Depending on the applied depression voltage, that results in

achievable total gyrotron efficiencies of up to 50 %. Of course, that is sufficient for present plasma

fusion experiments. But, future fusion power plants, such as the demonstration tokamak DEMO will

require significantly better efficiencies (>60 %) to achieve a sufficient fusion gain factor.

One possibility to improve the total efficiency of a gyrotron is to use the so-called multi-stage

depressed collector (MSDC) technology. That technology is well known from TWT or klystron

operation. Those collectors use several intermediate steps of the depression voltage along the electron

beam axis. According to the author’s best knowledge, in case of gyrotron operation there are two

theoretical concepts of MSDC technology known: the one is making use of the non-adiabatic

trajectories of electrons in a strong magnetic field; the other is using a specific E x B drift of the

electrons [1]. Even though that several considerations about theoretical MSDC designs for gyrotrons

exist in the literature [2, 3, 4], there is not any successful implementation of that technology known

for gyrotron operation.

In frame of EUROfusion at KIT the technology of MSDC shall be pushed significantly forward.

Initial steps towards new concepts for MSDC have been done already in 2014. For example, the

theoretical optimal efficiency depending on the distribution of the electron energy has been calculated

and some conceptual simulations have been made. In this presentation, the results of analytical studies

and the latest state of the research will be presented.

Acknowledgement

This work is supported by the European Community under the contract of Association between

EURATOM and Karlsruhe Institute of Technology (KIT). It is carried out within the framework of

the European Fusion Development Agreement (EFDA). The views expressed in this publication do

not necessarily reflect the views of F4E or the European Commission

References

[1] Pagonakis, I.G., et. al., IEEE Trans Plasma Sci., vol. 36, no 2, pp. 469-480, Apr 2008

[2] Singh, et. al., IEEE Trans. Plasma Sci., vol. 27, no. 2, pp. 490-502, Apr 1999

[3] Ives, R. L., et. al., IEEE Trans. Plasma Sci., vol. 27, no.2, pp. 503-511, Apr. 1999

[4] Ling, G., et. al., IEEE Trans. Plasma Sci., vol. 28, no. 3, pp. 606-613, Jun. 2000.

Combined experimental and theoretical study of constriction threshold of large-gap AMF vacuum arcs

N. Wenzel1, A. Lawall2, U. Schümann2, and S. Wethekam3 1 Siemens AG, Corporate Technology, Günther-Scharowsky-Straße 1, 91058 Erlangen, Germany

2 Siemens AG, Infrastructure & Cities, Low & Medium Voltage Division, Rohrdamm 88, 13629 Berlin, Germany

3 Siemens AG, Energy Sector, Power Transmission Division, Nonnendammallee 104, 13629 Berlin, Germany

ABSTRACT In this work, we investigate the constriction threshold of axial magnetic field (AMF) stabilized vacuum arcs between copper-chromium (CuCr) contacts at gap lengths of about 40 mm. The experiments are performed in a synthetic test circuit with short circuit currents (50 Hz) of up to about 40 kA (rms). In the experimental setup, the spatial AMF distribution is varied by means of external Helmholtz coils which are installed coaxially with a pair AMF-type contacts. The AMF magnetic flux density in the contact gap is determined by 3D finite element computation. The resulting arc evolution is studied in a demountable vacuum chamber with a high-speed, high-resolution CCD video camera. The experimental data is compared to 3D transient simulations of the vacuum arc based on a two-temperature magneto-hydrodynamic model of the arc plasma derived from first principles without adjustable parameters. The plasma simulation delivers streamlines of plasma flow and current density, distributions of plasma density and temperatures, and the energy impact on the anode. Experiment and simulation show good agreement concerning the minimum AMF amplitude needed to obtain a diffuse vacuum arc to prevent anode spot formation. The results also provide a qualitative understanding of ring structures of the energy flux to the anode surface observed for the diffuse state of the arc. Primary = Vacuum Interrupters Presentation Style: Oral Speaker’s Name: Andreas Lawall or Norbert Wenzel

NEW ULTRA FAST EARTHING SWITCH (UFES) DEVICE BASED ON VACUUM SWITCHING PRINCIPLE

Dietmar Gentsch1

1ABB AG, Calor Emag Medium Voltage Products, Oberhausener Straße 33, 40472 Ratingen, Germany

e-mail: dietmar.gentsch@de.abb.com phone: +49 2102 121 685

ABSTRACT

In the low- and medium- voltage range the vacuum interruption principle has been well established since 30 years in series production. Based on this experience a new application of vacuum technology is being introduced for use in the medium voltage range. This paper presents the design principle and the performance of the Ultra Fast Earthing Switch (UFES) based on a vacuum insulation device as conceived by ABB Ltd.

The UFES design consists of two main sections: The vacuum device and the corresponding drive section to close the vacuum device. The vacuum device is divided into two separate ultra high vacuum zones to create at the one hand a double gap between both contacts in oder to enhance the dielectric performance significantly, and on the other hand to obtain redundant vacuums. The two vacuum zones are separated by applying a closed membrane between both contacts which can be opened by a ctivating the plug contact side and breaking through the membrane to close the self-blocking contact system within less than 1.5ms.

The UFES system was developed for medium voltage application up t o 40.5kV and the short circuit current up to 63kA. Both ratings are tested in accordance to the standard IEC 62271-102 at the KEMA laboratory. Furthermore the short-circuit rating can be extended in the short-time-current (STC) of up to 3s. The design, test results and the application in commercial solutions are being presented.

Primary = Vacuum Interrupters Presentation Style: Oral

Dielectric testing of HV vacuum interrupters during capacitive current switching

B. Baum1, H. Janssen1, V. Hinrichsen1 1Technische Universität Darmstadt, High Voltage Laboratories, Darmstadt – 64283, Germany

ABSTRACT

Vacuum circuit breakers are well established in the distribution voltage level due to their various advantages, e.g. frequent switching operations, low life-cycle-costs, excellent thermal arc quenching capabilities, and nearly maintenance free operation [1]. In order to establish this technology at higher voltages, the dielectric withstand capability must be increased. E.g. restrikes, while interrupting capacitive currents, have to be identified and reduced. In this work, a test setup to investigate commercially available high-voltage vacuum interrupters for test voltages up to 200 kV is presented and its features are discussed. In particular, the simultaneous measurement and analysis of field emission currents as well as micro discharges shortly after arc extinction will be presented. References [1] P.G. Slade “The vacuum interrupter: theory, design, and application”, CRC Press, 2008

Triggered spark gap with internal trigger delay circuit

Wolfgang Däumer, Peter Bobert, Frank Werner

EPCOS AG, A TDK Group Company

Rohrdamm 88, 13629 Berlin, Germany

O (oral presentation)

C (primary topic): Vacuum Interrupters and Spark gaps

A2 (secondary topic): Pulsed Power Switching

Abstract

Currently used triggered spark gaps for medical applications like lithotripsy and electric shock wave therapy ESWT are covered with government administration restrictions for an export control (article 3A228 of EU export control list for dual use electronic components). The export control is valid for switching components with peak currents >= 500A and breakdown delay time <= 15 µs. Triggered spark gaps fall under the export control because of their short delay times caused by the very fast development of the gas discharge avalanche. However for the applications in medical treatment these short breakdown delay times are not important.

A triggered spark gap device with build-in trigger delay circuit and a mechanism, called locking fuse, which disables the function of the whole component when trying to remove the delay circuit, is presented. The typical breakdown delay time will be increased to typical > 25 µs, so that the device is not covered by article 3A228. The typical operation voltage lies in the range between 8 kV and 20 kV, maximum peak currents up to 8 kA and long life time with more than 4 million impulses.

The build-in trigger head locking fuse mechanism gives the guarantee, that the trigger delay circuit cannot be short circuited without destroying the whole trigger connection to the main gap.

GIANT CURRENT DENSITY IN KOOPS-GRANMAT- IS IT DUE TO A BEC CONDENSATE AT ROOM TEMPERATURE?

Hans W. P. Koops, HaWilKo GmbH, Ober-Ramstadt Germany

hans.koops@t-online.de

Koops Gran Mat® surpasses all known materials in carrying giant current densities and anomalous high currents. The values are much higher than for normal metals ( Au: < 250 KA/cm,²), and in high TC superconductors using Cooper pairs (Bosons) at 70K (Ti-doped MgB2 < 1 MA/cm² (1]), and as high or even higher than Carbon Nanotubes and Graphene (1 GA/cm²) at 300 K[2]. CNT and Graphene have overlapping electron states- which allows BEC at room temperature- but are limited by phonons influence from the substrate( M. Fuhrer [3]). In field emitter tips emission currents > 3 GA/cm² were experimentally measured (Pt/C, and Au/C- nanogranular materials produced by FEBIP – Focused Electron Beam Induced Processing,[ 4] 1994, and [5] 2000. The nanocrystals in the material have 2 nm or 4 nm diameter, being embedded into a carbon matrix with Pt-crystals distances of < 1 nm. Crystal diameters ranged from 1.8 to 2.1 nm for the Pt/C material. The metal crystals are surrounded by surface electron orbitals states according to Bohr’s atom model with a perimeter length of 3-, 4-, 5- electron wavelengths of ca. 2 nm. The levels with 5 λ extend more than half into the carbon matrix and overlap in 3 dimensions to the same levels of the neighbouring Pt crystals. This forms even at room temperature a network of overlapping electron states of similar energy throughout the NGM material. The Eigenstates have energy level distances of 125 meV ( Pt/C) or 65 meV (Au/C) above the Fermi-level[6]. The energy difference corresponds to the measured activation energy for hopping of electrons into the material. The resistivity of the material has a negative slope with rising temperature. This is in contradiction to metal or semiconductor materials characteristics. According to Bose and Einstein, a BEC condensate immediately forms, if overlapping electron states exist in the material. In superconductors this condensate is occupied from Bosons: composed from 2 electrons and Bohr Magnetons with anti-parallel spins and have a diameter up t o 600 nm[7

1 P.C. Canfield S. Bud`ko Spectrum d. Wiss. Juni 2005 p. 56

]. Like in lasers an infinite number of Bosons can reside in 1 energy level in 1 state, and they are coherent. The possibility of charge transport also for neutral Bosons built from 1 electron and 1 hole exists. However the electrons and the hole, which attract each other must have the same spin, which balances the attraction of the two charges. This results in the same extended Boson diameter (up to 600 nm). Having a field emitter situation, where a high field is applied (7 10^7 V/cm) electrons can tunnel through the field into the vacuum. However Bosons, which reach the tip of the NGM tip first need to decay into electron and hole. The hole goes back into the NGM on the excitonic level to form a new Boson with any other free electron in this level.

[2]Chandramouli Subramaniam et al. Fig. 1 c, ” Nature Communications Vol.:4, 2202, 23.7.2013 3 M. Fuhrer quotedat page 3247 in “Seong Ki Lee et al in Nano Letters 2012 12 , 3472” 4 J. Kretz et al. Microelectronics Engineering 1994, 23, 477-481. 5 F. Floreani et al. Nuclear Instr. & Methods in Physics Research A 2002, 483, 488-492. 6 , H. W. P Koops et al. J. Vac. Sci. Technol. 1996, B14, 4105. 7 http://www.supraconductivite.fr/en/index.php#supra-explication

SELF-SCREENING EFFECT OF INDIVIDUAL CNT FIELD EMITTER WITH HIGH ASPECT RATIO

Wolfram Knapp Otto-von-Guericke-Universität Magdeburg / IFQ

Universitätsplatz 2, D-39106 Magdeburg, Germany wolfram.knapp@ovgu.de

ABSTRACT It is a w idely accepted fact, based on num erous experimental studies, that stand-alone CNT field emitter with high aspect ratio have very good e lectron emission properties, such as low threshold voltage, high emission current and current density, long-term stability and so on. B ut a surprising result of some measurements is a “st rong saturation” of electron field emission (FE) at very high emission current, e.g. IE > 100nA for an individual MWCNT (cf. [1], FIG. 2 and FIG 4), without CNT field emitter destruction! Because abrupt transitions are atypical for well-known FE limitations (e.g. space charge limitation, purely ohmic resistance limitation), a self-screening effect was assumed and investigated. At first, an elementary model for self-screening effect specifications was developed. Model-based simulations show, a current dependent emitter voltage drop is the reason for a dramatic changing of field geometry of the applied macroscopic electrostatic field. And so, without warning, the field emission characteristic changes transition-free in the self-screening limitation characteristic. In my contribution I present and discuss following results: - The reason of self-screening effect is the CNT emitter resistance and a resultant CNT voltage drop

at higher emission current (IE > 100nA for an individual CNT), how shown in [2] and [3]. - The outcome of this self-screening effect is a virtual cathode. - The virtual cathode has the geometry (3D geometry) of the equipotential surface of the emitter tip

potential (exact: potential of field emission area). In contrast, the real cathode surface (cathode substrate and CNT emitter surface) is only the equipotential surface of zero field-emission current.

- The enhancement factor is a function of (a) field-emitter geometry and (b) emission current [3]. - Self-screening limitation characteristic is quasi-stationary. It means self-screening limitation is a

dynamic effect between continuous operation field emission switch-off and switch-on, like a jitter function.

- Self-screening effect can measure very well on individual CNTs with high aspect ratio, high emitter resistance and in small vacuum gaps.

References [1] J.-M. Bonard, K. A. Dean, B. F. Coll, and C. Klinke, “Field Emission of Individual Carbon Nanotubes in the Scanning Electron Microscope”. Phys. Rev. Letters 89, 19 (2002), p. 197602-1. [2] E. Minoux et al., “Archieving High-Current Carbon Nanotube Emitters,” Nano Letters 5, 2135 (2005). [3] L. Hudanski et al., “Carbon Nanotube based photocathodes,” Nanotechnology 19, 105201 (2008).

A fully kinetic and self-consistent simulation of a HEMP -thruster using a statistical approach for solving the “anomalous electron transport” problem

Günter Kornfeld1

Kornfeld Plasma & Microwave Consulting

The paper provides information about the authors developments on simulations of HEMP-thrusters with no further assumptions than geometry and magnetic field configuration, the applied anode voltage, the Xe gas flow and the neutralizer current, all defined in an input file. The major plasma collision processes should be implemented in the code. The selected baseline code was XOOPIC, an open source 2d3v plasma simulation code written in C++ and developed by the Plasma Simulation Group around Charles K. Birdsall and John Verboncoer at the Berkeley University of California. Starting from their internet version 2.70, dated 11-Jul-2012 and the corresponding XGRAFIX version 2.70.2, which enables the use of comfortable simulation diagnostics, the author implemented in the source code modifications and additional modules required for meaningful simulations of the HEMP- thruster:

exception treatment for neutral (zero charge) particles in the code to allow for continuous supply of neutral Xe particles for unlimited time simulations, correction of the “plasma source” module for proper functioning (used as neutral gas source), multiple background gases (NGDs) for neutral Xe0 and single charged Xe1+ implemented in the

code and the input file, addendum of the initial background gas densities (NGDs), which are used up with time, with the

time depending respective local particle densities “ rhoSpecies ” for Xe0 and Xe1+. In addition to the single ionization of those gases, leading to Xe1+ and Xe2+ ions, introduction of

one step double ionization collisions producing Xe2+ and Xe3+ ion particles respectively, introduction of a removal procedure for Xe0 and Xe1+ particles after ionization process, introduction of elastic collisions between neutral Xe0 particles.

In an input file, the geometry of a fictive HEMP- thruster and its plume region is split in a grid of axial 256 times 128 radial cells. A pronounced geometrical downscaling with a factor =1e-4 was selected. According to the scaling laws for the Maxwell equations all scaled particle trajectories remain unchanged if following applies: Distances d' = * d, fields E' = -1 * E and B' = -1 * B, whereas the potentials, velocities and currents remain unchanged. Thus for the simulation time step we have dt' = * dt and select dt' =1e-15 s to observe the Courant condition. To gain on the particle number and simulation time, we don't scale the currents invariant but start with I' = * I and the initial neutral pressure not like p' = -3 *p but like p' = -1 *p. The latter, physically follows Paschen law p'*d' = p*d, which keeps the collision probability along a certain particle trajectory constant. With these scalings, the selected grid cell dimensions are in the order of the Debeye length.

Remaining problems due to insufficient electron cross field transport required additional code work. They were found to result from an incorrect over-interpretation of colliding electron coordinates in the standard Monte Carlo collision modules, as used also in the baseline XOOPIC code. Those codes assume, that the starting coordinates of primary and created electrons after collision are identical to the coordinates of the incoming, colliding electron, thus binding the new or scattered electrons again to the same magnetic flux line in a magnetized plasma. As will be explained, this assumption is not justified within the scope of a uniform particle density inside the cells and the granularity of the number of particles np2c represented by a computer particle. In fact the locations of the outgoing electrons are only known to be within the same grid cell and therefore should be randomly selected within the cell where collision occurs.

It will be shown, that using this approach without artificial assumptions on anomalous electron transport, allows realistic simulations of a HEMP-thruster at very low currents (10-4 to 3*10-3 from nominal 1.5 A) . This has not only a physical similarity value for nominal operation but the method seem to allow investigation of the operational regime at the low edge of the dynamic range of a thruster. __________ Corresponding author, E-mail: guenter.kornfeld@t-online.de

X-Band Hollow-Beam Klystron Design with Corkscrew-Modulation

Jiwei Nie, Heino HenkeTechnische Universität Berlin, Sekr. EN-2, Einsteinufer 17, Berlin, 10587, Germany

André GredeHüttinger Elektronik, Boetzinger Str. 80, Freiburg, 79111, Germany

Abstract: A hollow-beam klystron with corkscrewmodulation has a series of advantages. Here, a tentativedesign of a high efficient klystron at x- band is given. Withthree gaps an extraction efficiency of 50% was achievedfor a 100 kV, 10 A beam. The power gain is 49 dB.

Keywords: Traveling wave tube; vacuum electronics;hollow beam

I. IntroductionThe hollow beam corkscrew modulated klystron is basedon an annular beam which is velocity modulated in a ringcavity operating in a rotating TMm10 -mode. As a result thebeam develops a density modulation in the drift-space ofcorkscrew shape. The advantages of an annular beam arerelated to the larger beam cross section area and largercavities. Here, we give a first design of a klystron withinput cavity, an idler cavity and a three gap output cavity at10 GHz, Fig.1. Eigenvalue and PIC simulations have beenperformed with the code GdfidL[2].

Figure 1. Schematic drawing of the klystron. In- and outputcavities with four coupling lines and idler cavity (all in red),

beam pipe (green) and three chokes (golden)

II. Design with TM110-Mode CavitiesIn a first step the three gap output cavity was designed. Thebeam has a current of 10 A and a voltage of 100 kV, i. e. anormalized velocity of β=0.55. The modulation degree ofthe beam is 5%. For cavities with more than one gap weneed π-phase shift between cavities and a good coupling.So four magnetic coupling slots were chosen at the highmagnetic field position near the outer conductor in thecavity. The extraction efficiency is seen in Table I.

Table 1. OUTPUT POWER AND OUTGOING BEAMVELOCITY β IN ONE TO THREE GAP CAVITIES

cavity output power βOne gap 210 kW 0.35Two gaps 310 kW 0.2

Three gaps 465 kW 0.13

The bandwidth of the three gap cavity is about 4.6%. Thenthe normalized velocity decreases from originally 0.55 to0.13 after the third gap. All simulations are done with asingle cell modulating cavity.

The input cavity has a loaded Q of about 285. A modulationfactor of 0.45% has been achieved with 7 W input power.An idler cavity was added to increase the modulation andthus the gain. It has the same geometry as the input cavitybut is tuned 1MHz higher than the input cavity, such thatthe voltage has 70° phase shift ahead of the current. TheQ-factor is 6300. The idler increases the beam modulationto 5.1%. and the bunching of the beam. The possible powercoupling between cavities were suppressed by radial chokelines close to the cavities, Fig. 1. The distances between thecavities are determined to assure maximum efficiency. Afull PIC has been done and 500 kW RF power could beextracted from the beam. The power gain is 49 dB. In- andoutput cavity are connected to a four transmission linenetwork.

A preliminary design of a hollow beam gun is also given. Itturns out that compression is not necessary.

III. Design with TM310-Mode CavitiesAlternatively, cavities operating in a TM310-mode wereconsidered. In that way the current could be increased to50A. Also, the output cavity is modified to four gaps andelectric instead of magnetic coupling. The extractionefficiency is now 50.2%.

References1. A. Grede, H. Henke, Concepts for circular deflection modulated tubes and frequency multiplying millimeter wave sources, IEEE Intern. Conf. IVEC 2009, Rome, pp 552 – 5532. Warner Bruns, http://www.gdfidl.de/

Broadband Traveling Wave Tubes in Ka- grants modern communication

E. Bosch, A. Laurent, P.Ehret, Jean Gastaud THALES Electron Devices, 78141 Vélizy (France) and D-89077 Ulm (Germany)

Email: peter.ehret@thalesgroup.com, alain.laurent@thalesgroup.com, Ernst.bosch@thalesgroup.com; jean.gastaud@thalesgroup.com

Abstract: The paper presents the capability of THALES Traveling Wave Tubes (TWT) for broadband satellite applications in Ka-band.

In the last years on the communication market a significant increase of data transfer has been recognized. The frequency needs shift step by step from C-band to Ku-band and now is using the full Ka-Band. Based on this continuing trend the satellite infrastructure has to provide a flexible and broadband solution for the communication equipment. The RF amplifier has a key role in the definition of the performance. The Traveling Wave Tube technology is able to support the broadband characteristic. THALES provides a portfolio of TWTs which will cover the need of the payload manufacturers. THALES has an outstanding experience in developing and manufacturing Traveling Wave Tubes and can demonstrate an impressive in orbit heritage. This tremendous experience was baseline for a full portfolio in Ka-Band from lower power up to 170 W and 250 W under development.

Keywords: Traveling Wave Tube; TWT; broadband; Ka-band, high power Ka-band TWTs

Introduction The trend on the communication market is requiring continuously more and more data. New applications are being installed and the amount of information exchange is increasing day by day. This demands signals in high quality and high channel capacities. As the end user is increasingly dependent to have access to the data at any time and everywhere, high reliability of the data transfer is also very important. For satellite applications the system architecture has to use broadband equipment. Also the trend towards higher output power and higher frequency has to be realized. For decades THALES Traveling Wave Tubes demonstrate beside the high reliability in orbit that this technology can effectively be adapted to the demand of the payload performance requirements. In the running THALES production program and development programs in Ka-band for higher power increased bandwidth the results show an nice efficiency improvement. In spite of necessary modifications of the design mainly due to increased output power the heritage is always respected. The THALES portfolio will be completed with broadband designs covering the total Ka-Band and the new designs will cover up to 2.9 GHz bandwidth in the output power classes up to 250 W. This will give the flexibility to the

customers in channel bandwidth or channel allocation within the band. Also an optimization for narrowband application can be done. Radiation cooled versions will be in the portfolio as well as conduction cooled versions.

TWT broadband needs in Ka-Band The high data transmission and large through put on the satellite requires wider Channel bandwidth resulting in mostly the full available bandwidth in Ka-band ( 2,9 Ghz) frequency. Beside the increase of the bandwidth the behavior has to be well balanced and with low linearity impacts to allow linearizing the signal. The leads to strong efforts on the TWT design.

TWT broadband performance In the following the latest results of the THALES development tubes in Ka-band will be shown. It will be concentrated on performance over frequency. To be able to use advantages from a broadband amplifier the most important parameters are symmetrical and flat behavior vs frequency of RF output power, DC input power and gain.

In Ka-band first the current 130 W design has been updated by a new helix taper design. An improvement by +2% total efficiency has been demonstrated. Qualification status is given by a heritage to big number delivered and in orbit operated tubes. The design is introduced into production since beginning 2014. Shown in the figure is the performance for 2 GHz bandwidth. The max phase shift at highest frequency is 53 deg.

As the market demands an increase of the output power THALES performed an development program to be

prepared to offer 170 W output power over the complete Ka-band (2.9 GHz bandwidth). In the next figure results of one development tube is presented.

The maximum phase shift is 55 deg. The radiator size is 185 mm. The radiation cooled version is going to be offered to the market in 2015. The conduction cooled version is already available.

The trend of the market for the future to higher output power will continue. To be prepared THALES has started development programs for the 250 W class. Both radiation cooled and conduction cooled designs will be offered. The qualification for the radiation cooled version will be finished in 2017 and for conduction cooled in 2016. The radiator size is defined with 210 mm. First development tube results are already available. These can be seen in the

next figure. The total phase shift is 55 deg at highest frequency.

Conclusion: The paper describes the design improvements achieved in the full Ka-band power range and will be extended to higher power in the full paper. The results today are fully in line with the expectation of broadband requirements and extent the large portfolio of Thales TWTs from L to V-Band with high efficiency and low non linearity’s.

THALES 150 W C-BAND TRAVELLING WAVE TUBES

W. Dürr, C. Dürr, P. Ehret, E. Bosch Thales Electronic Systems GmbH, Söflinger Strasse 100 - 89077 Ulm - Germany

ABSTRACT

Since recent years a clear trend has emerged on the world market of travelling wave tube (TWT) to higher output power, increased bandwidth and higher efficiency. With raised output power the payloads have possible reach the limit with dissipated power and the wish for radiation cooled C-band tubes will expressed by the payload manufactures. Competitors have shown in other frequency bands their strength and it can be expected that they will also introduce a high performance C-band tube with improved efficiency in near future. For this reason it is very important for Thales to introduce a new generation of radiation cooled TWT. Design characteristics The TL4150R is designed to operates at full frequency range of 3.4 - 4.2 GHz for downlink commercial communications to cover future market needs, provides a typical RF output power of 150 W CW, providing sufficient margin und specified operating conditions. The development was focused on the thermal management, the RF characteristic and new subassemblies components. The high power gun is designed with higher beam compression and higher output power and is equipped with a positive ion barrier to protect the cathode and increase life time. Additional performance for future output power increase will be also secured. The new line is improved to increase the RF bandwidth up to 800 MHz, to increase tube efficiency and to avoid oscillation to guarantee stable operation. Introducing a new innovative 5 stage collector into the C-band TWT family rises the overall efficiency at 150 W up to 74% on selected channels. Using the tube in wideband mode 71% efficiency is possible. The RF input and output are matched to archive a VSWR lower than 1.33:1 (17 dB) between 3.4 – 4.2 GHz. To handle multipaction at lower frequencies the output transition (TNC-connector) is changed in size and diameter. Performance Results The TWT can be operated over the entire frequency band (800 MHz) with the same voltages. By adjusting the voltages the RF performance can be optimized for selected frequency channels. Typical small signal gain values are at 60 dB for 150 W output power. The phase shift at 4.2 GHz is approx. 52°. Conculsion The predevelopment phase was very successful. The C-band TWT performance is significantly improved, not only a higher output power was achieved, but also an improved overall efficiency and an improved bandwidth performance. Qualification, additional margin, reliability tests and life tests are the upcoming task to finalize the product.

676869707172737475

3,4 3,6 3,8 4 4,2

TL4150 BB4 TL 4115 SN86

Bead-Pull Measurement of a W-Band Folded Waveguide StructureHeinrich Büssing1, André Grede2, Heino Henke1

1Technische Universität Berlin, Einsteinufer 17, 10587 Berlin, Germany2Hüttinger Elektrotechnik, Bötzinger Straße 80, 79111 Freiburg, Germany

AbstractThe paper presents a simple and cheap bead-pull measurement technique for W-band traveling wave structures.

KeywordsField Measurement, Traveling wave tube, vacuum electronics.

IntroductionAlthough modern simulation techniques are very powerful and are the standard procedure for designing electron tubes, one still has to verify the fabricated structure by cold measurements. Here a simple and cheap bead-pull technique for traveling wave tubes is presented. It determines the electric field along the beam pipe axis and allows for calculating the interaction impedance by integration.

Network analyzerTo measure the reflection in magnitude and phase with a scalar network analyzer, four measurements have to be done with the reflected signal self interfered at 0, 90°, 180° and 270° by an adjustable short as shown in fig. 1.

Figure 1. Simulated vector network analyzer, using directional couplers, a combiner and an adjustable short to self interfere the reflected signal.

Measurement MethodIn this example the perturbation measurement is applied to a folded waveguide traveling wave tube at w-band (90 … 98GHz) as shown in fig. 2a and b. A 50µm Al bead on a 8µm kevlar fiber (fig 2c) is pulled by a stepping motor through the beam pipe (z-direction) and the reflection parameter s11 is measured in magnitude and phase. The electric field at position z is calculated in (1), where the factor k is achieved by both, simulation and measurement.

E ( z)=k⋅√Δ s11(z)=k⋅√ s11with bead ( z)−s11without bead (1)

The magnitude of the electric field is shown in fig. 4a. The voltage an electron experiences on it its way along the beam pipe with a certain velocity ß is

V eff=∫0

zmaxej ωβc0

z⋅E dz (2)

This Veff is shown in fig. 4b for different ß.

p h

b

d

Figure 2a. Two halves of a W-band folded waveguide structure.

Figure 2b. Zoom into the 0.9mm deep serpentines with b=0.3, h=0.6, p=0.55, d=0.4mm

Figure 2c. 50µm metal bead on a 8µm kevlar fibre. 1mm distance between markers of the ruler.

Figure 4a. Magnitude of electric field at 92GHz along the beam pipe.

Figure 4b. The voltage an electron experiences on its way along the beam pipe computed with (2) for different velocities ß. The synchronous velocity is at ß=0.2445

References[1] A. Grede, H. Henke, R. K. Sharma, "RF-structure

design for the w- band folded waveguide TWT project of CEERI", IEEE Proc. IVEC 2011, Bangalare, pp. 213-214

[2] Charles W. Steele, “A Nonresonant Perturbation Theory”, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-14, No. 2, February 1996

[3] Warner Bruns, http://www.gdfidl.de/

-80 -70 -60 -50 -40 -30 -20 -100

20

40

60Electric Field along Beam Pipe Measured at 92 GHz

Distance in mm

|E| i

n kV

/m

-3dB

DUTTerminator

-10dBf

6fSweeper Multiplier

Control Unit

-10dB Combiner

ReflectionReference

Diode Detectors

Directional Couplers

Adjustable Short

0.15 0.2 0.25 0.3 0.350

2

4

6x 10

6

ß

Synchronous Velocity

V eff

Simulation of Beam-Wave Interaction in Filter-Type Slow Wave Structures

of Travelling Wave Tubes

Philip Birtel 1

, Elke Gehrmann2, Sascha Meyne

2, Arne F. Jacob

2

1Thales Electron Devices, Söflinger Straße 100, 89077 Ulm, Germany

2Technische Universität Hamburg-Harburg, Institut f. Hochfrequenztechnik, 21073 Hamburg, Germany,

ABSTRACT

Accurate numerical simulation tools are a critical requirement for the design of competitive travelling

wave tubes (TWTs). While there are commercial solutions to this task, these are general-purpose tools

that have simulation times of many hours or even days, making them impractical for design work.

Instead, a manufacturer of TWTs, such as Thales Electronic Systems, has to create special-purpose tools

with a very limited range of applicability, but with simulation times several orders smaller. There is an

ongoing DLR-funded cooperation with the TU Hamburg-Harburg to extend and improve the programs

that compute the beam-wave interaction in filter-type slow-wave structures (SWS). An interaction tool

for folded-waveguide SWS (“KLYSTOP”), and an interaction tool and a design method for filter helices

are two recent results of this cooperation.

A folded waveguide SWS consists of regularly spaced

and alternately oriented “teeth” that form the eponymous

waveguide. A hole for the beam is drilled through the

teeth. The folded waveguide has a limited pass band for

propagating waves, which makes it akin to the more

expressively discrete coupled-cavity SWS. However, due

to the large number of teeth (~100) the exchange of

energy between beam and wave is continuous, like that in

a helical SWS. In order to account for that somewhat hybrid nature of the folded waveguide, an accurate

equivalent-circuit model of the SWS was developed, and a suitable convergence method (quasi-Newton)

was employed for the interaction program. Also, considerable work was done on the transition and sever

elements [1]. The accuracy of the thus extended simulation program was demonstrated by comparison to

measurements.

The “filter helix” is a method to selectively suppress the harmonic

of the operating signal, which is created by the nonlinearity of the

beam-wave interaction, in order to increase the efficiency of the

device. It consists of a section of the helical delay line in which the

pitch of the helix periodically and abruptly changes, thus creating a

stop band at the harmonic, while propagation and amplification at

the operating frequency is unimpeded. The effects of the filter are

simulated by assuming both a forward and a backward travelling

wave, which are coupled via reflections occurring at the pitch discontinuities. The filter helix has now

been successfully employed in a 500W S-Band TWT in order to extend its operating band towards lower

frequencies, where the harmonic is especially strong [2].

[1] S. Meyne et. al., in Proceedings of the 15th International Vacuum Electronics Conference, Monterey,

April 2014, IEEE, pp. 15-16.

[2] E. Gehrmann et. al., IEEE Trans. on Electron Devices, Issue 6, Vol. 61 (1014), 1859-1864

HOT MATCHING ANALYSIS OF A GENERIC TWO-SECTION COUPLED-CAVITY

TRAVELING-WAVE TUBE

Sascha Meyne1, Jean-François David2, Arne F. Jacob1 1 Institut für Hochfrequenztechnik, Technische Universität Hamburg-Harburg, Hamburg, Germany

2 Thales Electron Devices, Vélizy, France

ABSTRACT

Coupled-cavity traveling-wave tubes (CC-TWTs) provide large output power with high efficiency at

microwave frequencies. It is important to study the matching condition of CC delay lines with and

without electron beam to understand the implications on the tube performance. Considering the trend

towards higher frequencies, delay lines such as folded waveguides (FWG) are currently investigated.

They can be modelled in a similar fashion as CC delay lines, so the analysis presented here is directly

applicable to FWG-TWTs.

Normally, the cold match of a delay line, i.e., without electron beam, is optimized in order to ensure

stable and efficient operation. However, the matching changes during operation due to the presence of

the modulated electron beam [1]. Thus, an effective characteristic impedance change has to be

considered to predict stability and performance of the tube [2, 3].

In this contribution a generic CC-TWT with two sections is considered (Figure 1). The tube consists of

nine and eleven cavities, respectively, and has couplers at the in- and output as well as severs between

the two sections. An ideal hot match derived from a small-signal interaction model is applied to couplers

and severs at each frequency. The matching condition is thus defined by the characteristic impedance of

the coupled beam-wave system. Therefore the couplers and severs are assumed to exhibit the proper

frequency dispersion. Although this might be a somewhat idealized assumption, several important

practical conclusions can be drawn.

Interaction is simulated with small- and large-signal models. Stability and amplifier gain are analyzed.

The results confirm that the matching condition derived from the small-signal model leads to residual

reflections under large-signal operating conditions. Nonlinear effects which are not included in the

calculation of the matching condition are shown to play a major role in this case and thus determine the

tube performance.

References

[1] S.O. WALLANDER, IEEE Transactions on Electron Devices Vol.19 No.5 (May 1972), pp. 655, 660

[2] S. MEYNE, J.-F. DAVID, and A.F. JACOB, in Proceedings of the German Microwave Conference

(GeMIC), Aachen, Germany, March 2014

[3] S. MEYNE, J.-F. DAVID, and A.F. JACOB, in Proceedings of the IEEE International Vacuum

Electronics Conference, Monterey, CA, April 2014, p. 15.

Figure 1: Generic two-section CC-TWT