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Choke-mode Damped X-band Structure for CLIC Main Linac Hao ZHA, Jiaru SHI CERN Sep 27, 2011 Jiaru Shi, LCWS11 Workshop, Granada1.

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Presentation on theme: "Choke-mode Damped X-band Structure for CLIC Main Linac Hao ZHA, Jiaru SHI CERN Sep 27, 2011 Jiaru Shi, LCWS11 Workshop, Granada1."— Presentation transcript:

1 Choke-mode Damped X-band Structure for CLIC Main Linac Hao ZHA, Jiaru SHI CERN Sep 27, 2011 Jiaru Shi, LCWS11 Workshop, Granada1

2  Acknowledgement  Collabration between CERN and Tsinghua University in China  Ph.D Student visiting CERN for 6 months, ZHA Hao  Manufacturing capability at Tsinghua  Outline  The Idea of choke-mode-damping  Parameters Comparison with waveguide damping  Wakefield damping study  Future plans 2

3 The choke mode cavity  Progress at KEK and SLAC  Applications at Japanese XFEL 3

4 Radial Choke [1] Jiaru Shi, LCWS11 Workshop, Granada [1] A. Grudiev 4

5 Parameters [1] Jiaru Shi, LCWS11 Workshop, Granada CellNDSWDSCDS1mmCDS1.5mmCDS2mm Q Cu (0.83)4720(0.7)5129(0.75)5617(0.82) Vg / c (%) (0.9)1.12(0.85)1.04(0.79)0.97(0.73) R/Q (kOhm/m) (0.91)15.2(0.85)14.1(0.79)13.2(0.74) Rs (Mohm/m) (0.75)71.7 (0.59)72.3 (0.59)74.1 (0.60) E surfmax /E acc 1.93 H surfmax /E acc [mA/V]2.54.0(1.6)2.5 Pulsed T rise (K) Plused T rise in first 118MV/m [1] Based on CLIC-G middle cell [2] 250 ns, 100MV/m 5

6  Advantages  Lower pulsed surface heating, no magnetic field enhancement  Bonding joint at low magnetic field, no problem on the chamfer  Easy manufacturing, turning only  Considerations  Knowledge from SLAC [1],  small gap (1mm) severe breakdown / 4mm gap OK  different gap size  Prototype structures for high power test 6Jiaru Shi, LCWS11 Workshop, Granada

7 Damping simulation with Gdfidl/HFSS (Model in HFSS) Gap 1mm 2mm Good damping for first dipole Mode reflected by the choke, to be studied… E field, fundamental mode E field of a dipole mode that is reflected by the choke Impedance and wakefield simulated in Gdfidl 7

8 EM field Jiaru Shi, LCWS11 Workshop, Granada High H, Low E Zero H, High E Fundamental mode at 12GHz High order dipole at 30GHz 8

9 EM field after detuning with “bubble” Jiaru Shi, LCWS11 Workshop, Granada H H E E Fundamental mode tuned back to 12GHz By changing choke-length 9

10 Smith Chart 10 A B C A B C B C Bubble,+j∆ No effect when adding to infinity Off from open point Red: fundamental mode Blue; 3h-HOM

11 Model in HFSS for optimization 11 Port 1 Port 2 Absorber in radial line absorb in the radial line: sqrt( 1-S11^2-S21^2 )

12 Radial line absorption 12 Choke reflection

13 Results of “bubble-choke” s0.15m origin20~30 “Bubble- choke” 20~25 WDS6~ GHz  34GHz(in V/pC/m/mm)  Push the second peak, more and more

14 Smith chart “double” 14 A B C A B C B double 2*z C Red: fundamental mode Blue; 3h-HOM

15 “double choke”, “bottle-choke” 15 40GHz!50GHz!

16 First dipole 16 s0.15m origin20~30 CDS50~60 WDS6~8 (in V/pC/m/mm)

17 “Thin-neck bottle”  Blue: “1:1:3 bottle-choke”  Red: “3:1:3 thin-neck bottle-choke” 17 12GHz 52GHz Narrow passband!

18 Result of “thin-neck bottle” 18 s CDS- origin 20~2510~15 CDS2~40.5~0.8 WDS6~81~1.5 (in V/pC/m/mm) Note: applied to Tapered structure

19 Problem of the “thin neck”  220MV/m electric field in the choke gradient) 19

20 Impedance matching  Reduced field in choke: 1:1 to gradient; ½ as max surface iris.  Optimizing the depth, length, position of the step, try to match the 16G,18G mode 20

21 Absorption after impedance matching  Blue: “1:1:3 bottle-choke”  Red: “1.5:1:3 bottle-choke” with impedance matching 21

22 Result: 22 s CDS- origin 20~2510~15 CDS6~81~2.2 WDS6~81~1.5 (in V/pC/m/mm)

23 Possible design 23 Pin: 61.3MW Loaded gradient: 100MV/m CLIC-G TD24-Choke same irises Pin: 61.3MW Loaded gradient: 96MV/m

24 Summary Jiaru Shi, LCWS11 Workshop, Granada  Study choke as transmission line, with smith chart  Simple model in HFSS for optimization, also possible for a prototype to do RF measurement  Choke mode damping with comparable result to waveguide damping  Future plans  Finalize the alternative RF design with choke-mode damping that could possibly replace the baseline design  Propose wakefield measurement at SLAC  Prototype for high power test 24

25 Thank you! Jiaru Shi, LCWS11 Workshop, Granada25


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