1.7.2010 © 2010 universitÄt rostock | fakultÄt informatik und elektrotechnik hom coupler...

1.7.2010 © 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK

HOM Coupler Development

for SPL

U. van Rienen - H.-W. Glock

Universität Rostock - Institut für Allgemeine Elektrotechnik

4th SPL Collaboration Meeting jointly with ESS

30.6.-2.7.2010 Lund

1.7.2010

21.7.2010 © 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock

... coaxial couplers without fundamental mode filter

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HOM coupler for SPL - β=1 cavity needed, better than ...

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Given coupler design limitations

1.7.2010 © 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 3

23/02/2010

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Orientation and longitudinal position fixed (cavity construction efforts, space needed for tuner, ...)

(Inner) diameter (max.) 36 mm

Same design on both sides of the cavity

(De)mountable, not welded

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"Classical" LEP hook design as starting point


coaxial 50-Ohm-port(connector not modeled)

adjustable capacitive coupling

combined E-/H-field coupling,capacity couples to outer conductor

support carries liquid helium


original picture taken from (courtesy W. Weingarten):E. Haebel, “Couplers for cavities,” CERN Accelerator School: Superconductivity in Particle Accelerators, Hamburg, Germany, May 1995, p. 231 ff

Free design parameters


Free design parameters

– electrodynamical CAE

~ 20 adjustable parameters

CSTStudio© ver 2009/2010


Free design parameters – examples


Waveguide-Coax-Transmission used to assess coupling connection to external dump

coax

waveguide connection to cavity:TE11 – horizontalTE11 – verticalTM01 (esp. facc !)TE21 – pol. 1TE21 – pol. 2...


Waveguide-Coax-Transmission used to assess coupling – e.g. example geometry - dependence on hook rotation

coax - TE11: E par. coupler

coax - TE11: E ortho. coupler

60° good compromisefor both polarizations


Fundamental mode rejection – e.g. example geometry - dependence on hook rotation

minimum of transmission occurs, but not at 704 MHz – to be tuned !

coax - TM01 (couples to fund. mode)


Field distributions give hints for design – e.g. example geometry – E-field geometry @ 704 MHz

strong capacitive coupling between "hook" and outer conductor => depends directly on "hook" length


Status and plan

Description of fully parameterized coupler geometry available

Many (~20) degrees of freedom to be taken into consideration

Primary design criterion: notch filter to be tuned for fundamental mode frequency

Combination with cavity (as done for coaxial couplers), Q-determination with pole fitting algorithm

Further optimization according polarization sensitivity (mainly TE11, TM11) ...

... Current density / loss density ...

... and further constructive aspects (cooling, manufacturing)

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Some news regarding ESS and University of Rostock:



CERN-SPL*-Study, EUCARD**, DoHRo*** @ Rostock

CERN-SPL*:

HOM damping design for CERN-SPL-Study

EUCARD** – WP 10.5.3:

HOM distribution and geometrical dependencies (FLASH-1.3, FLASH-3.9, XFEL(?)) needed for HOM coupler signal based beam analysis

DoHRo*** – HOM:

-WP 1: HOM damping design for BERLINPRO

-WP 2: HOM damping design for ESS – high energy part of p-linac

-WP 3: Simplified electronics for HOM coupler signal based beam analysis

*CERN-SPL: "Design of HOM-Damping for CERN-SPL“; funded by German Federal Ministry of Research+Education, Project: 05H09HR5

**EUCARD: EU FP7 Research Infrastructure Grant No. 227579

***DoHRo: Dortmund-HZB-Rostock – "Innovative Technologien und Komponenten zukünftiger Teilchenbeschleuniger in Strahlungsquellen, funding approved by German Federal Ministry of Research+Education, Project: 05K10HRC


CERN-SPL*-Study, EUCARD**, DoHRo*** @ Rostock

Staff (% of FTE):

Prof. Dr. Ursula van Rienen ( ~ 5%)Dr. Dirk Hecht (administrative; now ~ 5%)Dipl.-Ing. Thomas Flisgen (80% EUCARD**, 20% teaching)

Rostock University

Dr. Hans-Walter Glock50% CERN-SPL*25% EUCARD**25% DoHRo***

Dipl.-Ing. Mirjana Ivanovska (50%, on pregnancy leave till Oct`10)Dipl.-Phys. Tomasz Galek (100%, Oct.`09 - Jan.`10, 50% July`10 – Dez`10)N.N.-PhD: (50%)

CERN-SPL*

N.N.-PhD: (50%)Dr. Carsten Potratz (100%, from July`10) DoHRo***

Funding:

*CERN-SPL: "Design of HOM-Damping for CERN-SPL“; funded by German Federal Ministry of Research+Education, Project: 05H09HR5

**EUCARD: EU FP7 Research Infrastructure Grant No. 227579

***DoHRo: Dortmund-HZB-Rostock – "Innovative Technologien und Komponenten zukünftiger Teilchenbeschleuniger in Strahlungsquellen, funding approved by German Federal Ministry of Research+Education, Project: 05K10HRC


Thank you for your attention.

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Additional stuff:

- solver overview- CSC principle - pole identification- Q-determination for coaxial couplers

1.7.2010 © 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 17

1804/08/2010 © 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen

Used Methods for S-Parameter-Calculation (updated)

Transient SolverHexahedral Grid

Frequency SolverHexahedral Grid

Frequency SolverTetrahedral Grid

Fast Resonant SolverHexahedral Grid

Pro

Con

tra

Broadband computation of S-

Parameters via FFT.

Weak coupling between

orthogonal modes in rotational

symmetric structures.

Many time steps are needed to

reach steady state due to large

time constants.

S-Parameters do not show the

notch effect of HOM coupler in

a reasonable manner.

Appropriate for structures with

high quality factors.

Weak coupling between

orthogonal modes in rotational

symmetric structures.

Long computational time,

because each S-Matrix has to

be computed for every

frequency sample.

Very dense mesh is needed for

HOM coupler.

Appropriate for structures with

high quality factors.

Less number of unknowns is

needed to describe HOM

coupler

Fast solver available for

tetrahedral grids.

Strong artificial coupling

between orthogonal modes in

rotational symmetric structures

(e.g. cavity), due to non

symmetric grid.

Appropriate both for structures with

high quality factors and coupler-like

set-ups.

Weak coupling between orthogonal

modes in rotational symmetric

structures.

Really fast

Significant violation of unitarity of S-

matrices below cut-off

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corrected both with a posteriori transformation and software updatecorrected both with a posteriori transformation and software update


Concatenation procedure based on scattering properties: Coupled S-Parameter Computation = CSC

Split structure in sections

Compute scattering (S-) parameters of all sections individually with appropriate solvers

Compute overall S-parameters as function of f with special algorithm*, applicable to any structure topology and mode number

Derive loaded Q-values from S-parameter spectra *: e.g.: H.-W. Glock, K. Rothemund, U. van Rienen: "CSC - A System for Coupled S-Parameter Calculations", TESLA-Report

2001-25 or K. Rothemund, H.-W. Glock, U. van Rienen: "Eigenmode Calculation of Complex RF-Structures using S-Parameters", IEEE Transactions on Magnetics, Vol. 36, (2000): 1501-1503 and references therein

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SPL-β=1-cavity:HOM-Qload from full setup computation of coax-coax-transmission

following Nov'09 SPL Meeting proposal: 30 mm diameter coaxial couplersDo they provide sufficient HOM damping without fundamental mode filter?

80 mm diameter shortened beam pipes

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Coax with antenna tip depth = 0:

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• to avoid extreme Q-values

• scaling in a second step using coupler section's S-parameters in order to reach design

fundamental mode Q


Entire transmission spectrum 0.65 – 2.80 GHz:- more than 400 resonances with wide Q-range

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Using Pole-fitting algorithm* to determine loaded Q's

fundamental mode passband - dots: cstStudio© computation - line: fit result

f/GHzS21/dB

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*: Hecht, Rothemund, Glock, van Rienen: "Computation of RF properties of long and complex structures", Proc. EPAC 2002

S21( f )ak

2 i f pkk Qk

Im pk 2Re pk


Pole-fitting algorithm: "Old" version

"Old" algorithm (see reference)

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f

f

S21/dB


Improved pole-fitting algorithm

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Improved algorithm - corrects for higher order contributions, but still not working in any casesee: IPAC10, WEPEC008: Glock, Galek, Pöplau, van Rienen: HOM Spectrum and Q-factor Estimations of the High-beta CERN-SPL-cavities

S21/dBf


Q-value of lowest modes for 0 mm antenna depth:

f/Hz

Q

fundamental mode: Q = 1.04 108

fits well to field matching based estimation(4.3 108 for single coupler, slightly different geometry)

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Q-value spectrum for 0 mm antenna depth:

f/Hz

Q

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Several HOM modes with Q values as high or above fundamental mode (holds also for reduced coupling) –

Couplers without filters are not an acceptable solution!

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