1. HOM Coupler Development for SPL
U. van Rienen - H.-W. Glock
Universität Rostock - Institut für Allgemeine Elektrotechnik
4th SPL Collaboration Meeting jointly with ESS
Lund
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK

2. ... coaxial couplers without fundamental mode filter
HOM coupler for SPL - β=1 cavity needed, better than ...
... coaxial couplers without fundamental mode filter
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 2

3. Given coupler design limitations
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
23/02/2010 3
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 3

4. "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
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 4

5. Free design parameters
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
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 5

6. Free design parameters – electrodynamical CAE
~ 20 adjustable parameters
CSTStudio© ver 2009/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 6

7. Free design parameters – examples
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 7

8. Waveguide-Coax-Transmission used to assess coupling
connection to external dump
coax
waveguide connection to cavity:
TE11 – horizontal
TE11 – vertical
TM01 (esp. facc !)
TE21 – pol. 1
TE21 – pol. 2
...
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 8

9. Waveguide-Coax-Transmission used to assess coupling –. e. g
Waveguide-Coax-Transmission used to assess coupling – e.g. example geometry - dependence on hook rotation
60° good compromise
for both polarizations
coax - TE11: E par. coupler
coax - TE11: E ortho. coupler
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 9

10. coax - TM01 (couples to fund. mode)
Fundamental mode rejection – e.g. example geometry - dependence on hook rotation
coax - TM01 (couples to fund. mode)
minimum of transmission occurs, but not at 704 MHz – to be tuned !
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 10

11. Field distributions give hints for design –. e. g
Field distributions give hints for design – e.g. example geometry – E-field 704 MHz
strong capacitive coupling between "hook" and outer conductor => depends directly on "hook" length
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 11

12. 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)
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 12

13. Some news regarding ESS and University of Rostock:
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 13

14. CERN-SPL*-Study, EUCARD**, DoHRo*** @ Rostock
HOM damping design for CERN-SPL-Study
EUCARD** – WP :
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
***DoHRo: Dortmund-HZB-Rostock – "Innovative Technologien und Komponenten zukünftiger Teilchenbeschleuniger in Strahlungsquellen, funding approved by German Federal Ministry of Research+Education, Project: 05K10HRC
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 14

15. CERN-SPL*-Study, EUCARD**, DoHRo*** @ Rostock
Staff (% of FTE):
Funding:
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 Glock
50% 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*
Dr. Carsten Potratz (100%, from July`10)
DoHRo***
*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
***DoHRo: Dortmund-HZB-Rostock – "Innovative Technologien und Komponenten zukünftiger Teilchenbeschleuniger in Strahlungsquellen, funding approved by German Federal Ministry of Research+Education, Project: 05K10HRC
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 15

16. Thank you for your attention.
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK U. van Rienen – H.-W. Glock 16

17. Additional stuff: - solver overview - CSC principle - pole identification - Q-determination for coaxial couplers
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 17

18. Used Methods for S-Parameter-Calculation (updated)
Transient Solver
Hexahedral Grid
Frequency Solver
Hexahedral Grid
Frequency Solver
Tetrahedral Grid
Fast Resonant Solver
Hexahedral Grid
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.
Appropriate both for structures with high quality factors and coupler-like set-ups.
Weak coupling between orthogonal modes in rotational symmetric structures.
Really fast
Pro
Strong artificial coupling between orthogonal modes in rotational symmetric structures (e.g. cavity), due to non symmetric grid.
corrected both with a posteriori transformation and software update
Contra
Significant violation of unitarity of S- matrices below cut-off
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 18 18

19. 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 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): and references therein
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 19 19

20. following Nov'09 SPL Meeting proposal: 30 mm diameter coaxial couplers
SPL-β=1-cavity: HOM-Qload from full setup computation of coax-coax-transmission
80 mm diameter shortened beam pipes
following Nov'09 SPL Meeting proposal: 30 mm diameter coaxial couplers
Do they provide sufficient HOM damping without fundamental mode filter?
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 20

21. Coax with antenna tip depth = 0:
to avoid extreme Q-values
scaling in a second step using coupler section's S-parameters in order to reach design fundamental mode Q
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 21

22. Entire transmission spectrum 0. 65 – 2
Entire transmission spectrum 0.65 – 2.80 GHz: - more than 400 resonances with wide Q-range
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 22

23. Using Pole-fitting algorithm* to determine loaded Q's
f/GHz
S21/dB
fundamental mode passband - dots: cstStudio© computation - line: fit result
*: Hecht, Rothemund, Glock, van Rienen: "Computation of RF properties of long and complex structures", Proc. EPAC 2002
04/08/2010
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24. Pole-fitting algorithm: "Old" version
S21/dB
"Old" algorithm (see reference)
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 24

25. Improved pole-fitting algorithm
S21/dB
Improved algorithm - corrects for higher order contributions, but still not working in any case
see: IPAC10, WEPEC008: Glock, Galek, Pöplau, van Rienen: HOM Spectrum and Q-factor Estimations of the High-beta CERN-SPL-cavities
04/08/2010
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26. Q-value of lowest modes for 0 mm antenna depth:
fundamental mode: Q =
fits well to field matching based estimation
( for single coupler, slightly different geometry)
f/Hz
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 26

27. Q-value spectrum for 0 mm antenna depth:
f/Hz
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!
04/08/2010
© 2010 UNIVERSITÄT ROSTOCK | FAKULTÄT INFORMATIK UND ELEKTROTECHNIK H.-W. Glock - Thomas Flisgen 27