1. Work summary in 2016 Hongjuan Zheng CEPC SRF WG Meeting
, IHEP

2. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

3. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

4. Cavity design Parameters Value Riris (mm) 78 Alpha (deg) 3.22 A (mm)
94.4
B (mm)
a (mm)
20.123
b (mm)
22.09
L (mm)
115.3
D (mm)
204.95 k
2.86%
R/Q (Ω) G
Ep/Eacc
2.38
Bp/Eacc [mT/(MV/m)]
4.17
Total loss factor [V/pC]
(σ=4 mm)
Cut off fre. (MHz)
TE11：1126
TM01：1471
Ref：
TESLA: Ep/Eacc=2, Bp/Eacc=4.26
LL：Ep/Eacc=2.38, Bp/Eacc=3.65

5. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

6. HOM coupler design Research target Beam stability: HOM Qe~104
HOM power:
If beam spectrum coincide with HOM, the requirement for Qe should less than 103. (For TM011, if resonance happen, Pt=300W (Qe=103))
Maximum power: 1 kW
Cut off TE11：1126MHz
Cut off TM01：1471MHz
HOM coupler bandwidth: 800~1400MHz
Dangerous monopole: aroud1200MHz
Dangerous dipole: 800MHz~900MHz, 1200MHz
HOM damper: ＞1400MHz

7. HOM power spectrum (H-LP)
HOM coupler design
HOM absorber bandwidth
HOM power spectrum (H-LP)
for comparison Q0 losses:
Ea=20MV/m Q0=1.2E+10 P=33.5W
HOM absorber focus on 1GHz~20GHz.

8. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

9. Broadband HOM coupler TM01-TEM
To design the coupler from equivalent circuit concept. Then transform to transmission line models (TLM).
To simplify the HOM coupler design by ABCD matrix.

10. 2-cell cavity with couplers
Monopole mode damping results
use average current to calculate the threshold
not include the frequency spread
For Z, 32 cavity used
TM020
TM011
Continue to optimize the broadband damping results
Increase the probe head area
Increase the insert depth

11. 2-cell cavity with couplers
Dipole mode damping results
use average current to calculate the threshold
not include the frequency spread
For Z, 32 cavity used
TM111/TE121
TE111
TM110
Hybrid
Continue to optimize the broadband damping results
Increase the probe head area
Increase the insert depth

12. Optimized design of probe type
TM01-TEM
TE11-TEM
Increase the area of the probe end:
The damping for TE111 mode is changed only a little.
The broadband damping becomes poor.
The notch filter effect for the fundamental mode also becomes worse.
New method need to be used.

13. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

14. Loop coupler: increase the damping results for TE111
cut off:TE MHz
cut off: TM MHz
Loop coupler: increase the damping results for TE111

15. HOM coupler position Angle between two HOM is 100 deg.
Face1
HOM coupler r=40mm
d=100mm h
h=70mm, power dissipated on face1 is
P1=0.157 mW*16=2.5 mW
When Q0=2E+10
Pc=12.5 W
Angle between two HOM is 100 deg.
The HOM coupler tube length is 70 mm.

16. 2-cell cavity with couplers
TM111/TE121
TM110
Hybrid
TM020
TE111
TM011
Beam parameters (wangdou )
Qe (CST) is the result with HOM couplers.
The other 3 Qe values are stand for the threshold for different design.
For H design, the Qe for the TM011 TM110-π/2 mode can not meet the requirement.
For H design, the Qe for the TM110-π/2 mode can not meet the requirement.
The damping for TE111 mode is perfect.
Not include the frequency spread influence!!!

17. Multipacting simulation
Ar discharge cleaned
No multipacting
Ar放电处理过的铌
Ar discharge cleaned
No multipacting

18. Tolerance analysis + (1) 提取内导体左右偏移 (2) 电容间隙上下偏移 (3) 钩子部分上下偏移
(4) 钩子部分左右偏移
(5) 钩子部分绕x轴旋转
(6) 钩子部分绕z轴旋转
水平及上下偏移误差±0.5 mm
旋转角度误差±0.5 deg.
(1)
(2)
(4)
(3)
(5)
(6)

19. 不同误差对高次模影响较小，对基模影响显著

20. Outline Cavity design HOM coupler design Summary Broadband coupler
Loop coupler
Summary

21. Summary 2-cell design HOM coupler RF design Next Thermal analysis
The damping for TE111 mode is perfect
The broadband damping results can meet the requirement
Next
Thermal analysis
Mechanical design ……