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J. HolmaCLIC Workshop, Jan 30, 20131J. HolmaAcknowledgement M.J. BarnesCERN TE/ABT

Present Status of Inductive Adder Development for the CLIC DR Extraction Kicker System1OverviewSpecifications for CLIC Pre-Damping Ring (PDR) and Damping Ring (DR) KickersCLIC DR Kicker Pulse DefinitionChallenges and IssuesLayout of the Kicker System with an Inductive AdderInductive AdderInductive Adder DesignSchematic of an Inductive AdderModulation schemesStatus of the DesignSchedule for PrototypingTests and Measurements of Prototype AddersJ. Holma2CLIC Workshop, Jan 30, 2013

(Selected) Key:DR Damping Ring;PDR Pre-Damping Ring. PDR & DR Kickers ( ): One injection and extraction system per ring and per beam (8 systems) Damping rings reduce beam emittance; hence kickers must be high stability (low ripple). Low beam coupling impedance is also required.CLIC General LayoutJ. Holma3CLIC Workshop, Jan 30, 2013 CR injection is by an RF deflector (NOT kickers). Dump kickers are NOT foreseen. CR only 3 passes, but impedance is an issue because of very high beam current. Turn around impedance is probably an issue -> Drive Beam passes through 24 TA kickers! Emergency kickers in drive beam => Similar requirements to CR & TA kickers.Compact Linear Collider (CLIC) study aims at a center-of-mass energy range for electron-positron collisions of 0.5 to 5TeV, optimised for a nominal center-of-mass energy of 3TeV (3TeV CLIC). In order to reach this energy in a realistic and cost efficient scenario, the accelerating gradient has to be very high - CLIC aims at an acceleration of 100MV/m. Superconducting technology being fundamentally limited to lower gradients, only room temperature travelling wave structures at high frequency (12 GHz) are likely to achieve this gradient.In order to optimize the production of sufficient RF power for this high gradient, and CLIC relies upon a two-beam-acceleration concept: The 12 GHz RF power is generated by a high current electron beam (drive beam) running parallel to the main beam. This drive beam is decelerated in special power extraction structures (PETS) and the generated RF power is transferred to the main beam. This leads to a very simple tunnel layout without any active RF components (i.e. klystrons). Both beams can be generated in a central injector complex and are transported along the linac.3DR Kickers: Selected CLIC (2GHzbaseline), ILC & DANE Parameters CLIC PDRCLIC DRILCDANEBeam energy (GeV)2.862.865 0.51Total kick deflection angle (mrad)2.01.50.75Aperture (mm)~402024[6] (tapered)54.8 (tapered)Effective length (m)2*1.71.720*0.32=~6.40.94Field rise time (ns)70010003~5Field fall time (ns)70010003~5Pulse flattop duration (ns)~160~160NANAFlattop reproducibility1x10-41x10-41x10-3??Flattop stability [inc. droop], (Inj.)per Kicker SYSTEM (Ext.)2x10-22x10-32x10-32x10-41x10-41x10-4????Field inhomogeneity (%) [CLIC: 3.5mm radius] [CLIC: 1mm radius]0.1 (Inj.)0.1 (Ext.)0.1 (Inj.)0.01(Ext.)??3 (x=27mm @y=0) 10 (y=10mm @x=0Repetition rate (Hz)50505 (3M burst)50Pulse voltage per Stripline (kV)1712.5545Stripline pulse current [50 load] (A)340250100900J. Holma4CLIC Workshop, Jan 30, 20134Takashi NAITO showed an estimated (measured) stability, of the kick angle, of 2x10^-3, see Fast kicker performance in ATF, Low Emittance Rings Workshop (LER2010), January 1215, 2010, CERN.M.J. Barnes & J. HolmaCLIC Workshop, Jan 30, 2013

5CLIC DR Kicker Pulse Definition Rise time: time needed to reach the required voltage (but includes settling time). 700-1000 ns allowed, less than 100 ns desired; Settling time: time needed to damp oscillations to within specification; Beam: 160 ns (for 2 GHz baseline, 900 ns for 1 GHz baseline) time window during which droop and oscillations must be within specification, however because of the kicker mismatch the pulse flattop may be required to be 310 ns (150 ns settling time); Flattop stability: maximum of 2x10-4 for combined droop and ripple of DR extraction. This corresponds to 2.5 V range for 12.5 kV output pulse for DR extraction; Reproducibility: maximum difference allowed between any two pulses, 1x10-4; Fall time: time for voltage to return to zero; Minimizing rise and fall times reduces stress on kicker system. To minimize settling time, impedance of system has to be well matched.

Challenges and IssuesSe 0.02 % requirement for the pulse flattop stability for DR extraction kicker is an extremely demanding specification:An order of magnitude better than in any existing systemsActive compensation of droop and ripple will be studied further with the prototypeImpedance mismatchesSuitable high precision measurements of the pulse in the laboratory

J. Holma6CLIC Workshop, Jan 30, 2013

0.02% Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)6Kicker System with an Inductive Adder and a Stripline Kicker J. Holma7CLIC Workshop, Jan 30, 2013

Schematic of kicker system with an inductive adderEven/Odd Mode Characteristic Impedance Due to even/odd mode characteristic impedance optimization (Seetalkby C. Belver-Aguilar: CLIC DR Extraction Kicker Design, Manufacturing and Experimental Program), the impedance of the kicker striplines will not be 50 ohm as seen by the adder:The even mode characteristic impedance (not pulsed, no virtual ground) is seen by the passing beam and this should be 50 ohmThe odd mode characteristic impedance (pulsed with different polarity pulses, virtual ground between striplines) is seen by the adder, 35-41 ohm. Therefore, the inductive adder will not be matched perfectly to the kicker striplines. Settling time of the reflections will be ~150 ns, therefore the pulse flattop needs to be at least ~310 ns! The prototype adders are designed for 1 s pulse width

FeedthruCeramic SupportBeam DANE Striplines (Taken from: D. Alseni, LNF-INFN, Fast RF Kicker Design, April 23-25, 2008.)Inductive AdderJ. Holma8CLIC Workshop, Jan 30, 2013Inductive Adder Solid-state switches; Control electronics referenced to ground; No electronics referenced to high voltage despite the high voltage output of the adder; Modularity: the same design can potentially be used for DR and PDR kickers despite the different specifications. The PDR version will require more layers in series; Redundancy and machine safety: if one switch or layer fails, the adder still gives a significant portion of the required output pulse; Possibility to generate positive or negative output pulses with the same adder: the polarity of the pulse can be changed by grounding the other end of the output of the adder; Source impedance is low, hence minimizing number of layers; The output voltage can be modulated during the pulse.Schematic of an inductive adder

Photo of an inductive adder

Operation Principle of an Analogue Modulation LayerM. Barnes, J. Holma9CLIC Workshop, Jan 30, 2013

In analogue modulation layer, there is no energy storage capacitor but there is resistor Ra Resistor Ra is effectively in series with the load Load voltage:

in which Vmax is the sum of the voltages over the layers except the analogue modulation layer, hence Vload Vmax. Resistor Ra is in parallel with magnetizing inductance Lm PASSIVE MODE: During the pulse, current through Lm increases, which causes current through Ra to decrease. Therefore, voltage over Ra decreases, which causes VLoad to increase. This voltage change is reverse in comparison with voltage droop caused by storage capacictors in other layers. ACTIVE MODE: A linear switch provides a shunt path for the current trough resistor Ra. Therefore, the voltage over Ra can be controlled by controlling the current through the switch.

No capacitor hereLinear switchVaVMaxVLoad Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)9 The analogue modulation layer can be used to generate: a ramp function into output pulse to compensate droop (shown in blue)an arbitrary waveform to compensate known ripple components (feed-forward control, shown in green)

Operation Principle of an Analogue Modulation Layer (contd)J. Holma10CLIC Workshop, Jan 30, 2013

VaVMax

VLoadwith a compensating ramp with a sinusoid and ramp compensation0.02%0.02%0.02% Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)10Status of the Inductive Adder Design The main detail studies of the inductive adder have been completed, including mechanical design of the adder stack and electrical design of the printed circuit boards (PCBs) The main components for the prototype adders have been ordered/received (pulse capacitors, transformer cores, semiconductor switches, gate drivers, high precision DC supply) The mechanical parts have been designed, ordered and partly received (yesterday) for two 5-layer prototypes The PCBs for the first 5-layer prototype will be layed out by CERN DEM in January-February 2013 and then manufactured. J. Holma11CLIC Workshop, Jan 30, 2013

Mechanical designOrdering of componentsElectrical designSchematic and layout design of PCBs Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)11Status of the Inductive Adder Design (contd) A (prototype) terminating load for testing the prototype inductive adders and the striplines is presently being sort (one possible supplier is Barth Electronics). The specifications are 50 , 12.5 kV, 150W(average), bandwidth: DC100 MHz. The 10-4 stability of the load during 160 ns long pulse needs to be verified by testing. On-going studiesMethodology to design the physical dimensions of the inductive adder structure so that its electrical parameters can be adjusted to meet the desired behaviour without several iteration steps. FastHenry code has been used to compute the inductances of primary circuits of the inductive adder. The code will be used further to compute coupling capacitance and secondary leakage inductance of the adder stack. The predictions will be verified with the first 5-layer prototype adder and, once verified, this approach can be used to design and fine-tune high performance pulse modulators in the future.J. Holma12CLIC Workshop, Jan 30, 2013

Barth Electronics HV attenuator (resistor) FastHenry model of primary circuit of an inductive adder Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)12Schedule for Prototyping and Testing The first 5-layer prototype adder will be assembled in February/March 2013 and testing will be started immediatelyMechanical parts and the main components have been ordered and most of them have been delivered. The printed circuit boards will be manufactured in January/February. A second 5-layer prototype is scheduled to be ready for testing shortly afterwards. This adder is needed to test compensation/modulation methods as well as stability of adders in the bipolar setup. In a kicker setup with striplines, negative and positive voltage pulses are needed simultaneously.The second prototype adder will be based on the updated design of the first prototype. A full size 20-layer, 12.5 kV, 250 A, inductive adder will be built and tested in June-August 2013The transformer cores and storage capacitors have already been ordered for this device. These components have the longest delivery times (~3 months) Components for the second 20-layer inductive adder will be ordered during 2013.The transformer cores and storage capacitors for this device have also been ordered. The design can be updated, if necessary, according to tests with the first 20-layer prototype adder. Tests with these two 12.5 kV, 250 A inductive adder and the striplines will start in 2014.J. Holma13CLIC Workshop, Jan 30, 2013

Parts of the first prototype adder Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)13

Tests and Measurements of Prototype Inductive AddersSeRequirements: Extremely flattop output pulse: 12.5 kV, 250 A, 160 ns with less than 0.02 % (2.5 V) of combined droop and ripple. Reproducibility and stability: the difference of the waveforms of consecutive pulses has to be within 0.01 % (10-4).Tests and Measurements to Demonstrate: New design methods for impedance modelling: 3D simulation of the inductive adder structure and printed circuit boards, to compute analytically the primary inductance, coupling capacitance and secondary inductance of the adder stack. To my knowledge, this is a novel, important and necessary step in achieving the required performance. New compensation methods: in order to reach the desired performance, analogue modulation (active and passive) will be applied to improve the output pulse using an analogue modulation layer in the inductive adder. Theoretical studies ,whose results I have previously reported, show that this approach should be effective. These studies are valuable for gaining experience in designing pulse modulators with very high performance. The results of the studies will be published in conferences in 2013. The prototype DR kicker striplines will be tested and verified with the prototype inductive adders.J. Holma14CLIC Workshop, Jan 30, 2013

Picoscope oscilloscope (12 bit, 100MHz)Bergoz current transformerPartial assembly of a prototype adder

Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)14

Questions?

J. HolmaCLIC Workshop, Jan 30, 2013

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Comments?

References and BibliographyHolma J., Barnes M.J.: Sensitivity Analysis for the CLIC Damping Ring Inductive Adder, accepted to be publ. in Proc. of Int. Power Modulators and High Voltage Conference, San Diego, CA, USA, Jun. 3-7, 2012.

Holma J., Barnes M.J.: Evaluation of Components for the High Precision Inductive Adder for the CLIC Damping Rings, Proc. of IPAC 2012, New Orleans, USA, May 20-26, 2012.

Holma J., Barnes M.J.: Pulse Power Modulator Development for the CLIC Damping Ring Kickers, CLIC-Note-938, CERN, Geneva, Switzerland, April 27, 2012.

Holma J., Present Status of Development of DR Extraction Kicker System, International Workshop on Future Linear Colliders, Granada, Spain, 26-30 Sept., 2011.

Holma J., Barnes M.J.: Preliminary design of an inductive adder for CLIC damping rings, Proc. of IPAC 2011, San Sebastin, Spain, 4-9 Sept., 2011.

Holma J., Barnes M.J., Ovaska S.: Preliminary design of the pulse generator for the CLIC damping ring extraction system, Proc. of 18th IEEE International Pulsed Power Conference, Chicago, Illinois, USA, 19-23 Jun, 2011.

J. Holma16CLIC Workshop, Jan 30, 2013 Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)16EXTRA SLIDESJ. Holma17Modulation SchemesSe

J. Holma18 Digital modulation:refers to switching on and off a layer, whose capacitors are precharged to a predetermined voltage, during the output pulse. This is a coarse method to modulate the output and cannot be used to compensate droop. However, turn-on of individual switches or layers may be initiated at different times to reduce ripple. Analogue modulation: a layer is used to compensate the droop of capacitors, significantly reducing the required capacitance per layer: Passive analogue modulation: a layer works effectively as an R-L circuit. However there is no ability to change the modulation on-line. Active analogue modulation: a layer uses linear switches, and can be used to modulate the flattop during the pulse and provides the ability to change the modulation on-line. Active analogue modulation requires linear semiconductor switches, therefore MOSFETs have been chosen as switches. PSpice simulations of the efect of the value of the capacitance per layer upon the flattop droop:(i) with no compensation, (ii) with RL-compensation and (iii) with active analogue modulation.

Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)18Double Kicker System: Concept (Extraction)J. Holma19KEK/ATF achieved a factor of 3.3 reduction in kick jitter angle, with respect to a single kicker, with single-bunch measurements.

Extraction with one kicker magnet: Requires a uniform and stable magnetic field pulse. Two identical pulses are required; One power supply sends the pulses to 2 identical kickers.Extraction with two kicker magnets:

1st kicker system for beam extraction; 2nd kicker system for compensation of jitter of deflection angle (ripple & droop) from 1st kicker; Figure shows 1st and 2nd kickers separated by a betatron phase of 2n: for a betatron phase of (2n1) the 2nd kick is in the other direction.(Kicker)(Anti-Kicker)Time of flightSeptum after 1st kicker not shown, but would be there (see next slide).19Example of Double Kicker System for DR ExtractionIn order that beam bunches and kicker field are synchronized in time at the 2nd kicker system, the two kicker systems are powered in parallel. However, additional lengths of transmission line are required to compensate for the beam-of-flight between the 1st and the 2nd kickers.Potential problems Different attenuation & dispersion of stripline waveforms (due to length of transmission lines); Differences between magnetic characteristics of kicker & anti-kicker; Imperfections in beam-line elements/alignment between kicker & anti-kicker.J. Holma20 1st kicker system (in damping ring) for beam extraction; 2nd kicker system (in extraction line) for jitter compensation.

Beam Time-of-Flight compensation. 2-D Model of Stripline KickerJ. Holma21

Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)21Operation Principle of an Analogue Modulation LayerM. Barnes, J. Holma22

In analogue modulation layer, there is no energy storage capacitor but there is resistor Ra Resistor Ra is effectively in series with the load Load voltage:

in which Vmax is the sum of the voltages over the layers except the analogue modulation layer, hence Vload Vmax. Resistor Ra is in parallel with magnetizing inductance Lm PASSIVE MODE: During the pulse, current through Lm increases, which causes current through Ra to decrease. Therefore, voltage over Ra decreases, which causes VLoad to increase. This voltage change is reverse in comparison with voltage droop caused by storage capacictors in other layers. ACTIVE MODE: A linear switch provides a shunt path for the current trough resistor Ra. Therefore, the voltage over Ra can be controlled by controlling the current through the switch.

No capacitor hereLinear switch Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)22Operation Principle of an Analogue Modulation Layer (contd)J. Holma23

VaVmax

Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)23Other Issues: Machine safetySe If only one of the two striplines is powered, beam will receive ~1/2 deflection; high intensity beam could cause considerable damage to other equipment. This could result if a single switch were used for each stripline: an inductive adder (multiple primary switches) will help to avoid this problem.

Fast rise and fall times of field are desirable; e.g. if beam is mis-timed, with respect to the kick pulse, a fast rise/fall time will result in beam being swept faster across downstream materials/devices, minimizing potential damage.J. Holma24 Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)24Contributors to Instability/Ripple & Droop Kicker System - Electrical Charging power supply (not expected to be a major contributor for slow charging of PFL); Pulse Forming Line (PFL) and transmission lines [attenuation and dispersion]; Switch (dynamic characteristic and temperature effects); Transmission line [attenuation and dispersion]; Feedthroughs (impedance mismatching) Terminating resistor (frequency dependence of value and temperature effects); Impedance matching of system.Others Long-term temperature effects (e.g. switches for LHC kicker dump generators ~0.2%/C ambient); Inhomogeneity of integrated field (integrated in beam direction);

Although every effort will be made to minimise droop & ripple, it may be present at a level above that of the specification (0.2% / 0.02%). Hence, a novel pulse generator may be required as well as a double kicker system.

FeedthroughsSchematic of one possible stripline kicker systemJ. Holma25The specifications for the pre-damping rings and the damping rings include:low longitudinal and transverse beam coupling impedances;high stability and reproducibility of the field;excellent field homogeneity;ultra-high vacuum.

FeedthruCeramic SupportTaken from: D. Alseni, LNF-INFN, Fast RF Kicker Design, April 23-25, 2008.BeamElliptical cross-section (increases deflection efficiency).DANE Striplines (~0.9m) J. Holma26Note: each taper 30% of overall length. Stripline structures will be used for the kicker element; CIEMAT & IFIC, in conjunction with CERN, are carrying out a complete optimization of the design of the DR striplines; Spanish Industry (TRINOS) will produce manufacturing drawings and a set of prototype DR striplines; The striplines will be supplied with suitable high voltage vacuum feedthroughs.Brief Summary of Stripline Design26Stripline Design: Longitudinal Impedance

Longitudinal beam coupling impedance for untapered (Chao) and tapered stripline kicker (S. Smith, SLAC):

Virtual Ground+ve-veBeam pipe GroundStriplines driven to same magnitude, but opposite polarity, voltage, to extract beam.Total capacitance (C) is given by: capacitance between a stripline and virtual ground capacitance between a stripline and beam-pipe ground

+/-ve+/-veBeam pipe GroundBeamSame polarity and magnitude of current / voltage induced on both striplines by beam. Capacitance (C) is given by: capacitance between a stripline and beam-pipe ground

Without dielectric or magnetic materials:

27LR2011, October 3-5, 2011 M.J. Barnes27Bunches

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