Work summary in 2016 Hongjuan Zheng CEPC SRF

Work summary in 2016 Hongjuan Zheng CEPC SRF WG Meeting 2017 -01 -17, IHEP

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 2

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 3

Cavity design Parameters Riris (mm) Alpha (deg) A (mm) B (mm) a (mm) b (mm) L (mm) D (mm) k R/Q (Ω) G Ep/Eacc Bp/Eacc [m. T/(MV/m)] Value 78 3. 22 94. 4 20. 123 22. 09 115. 3 204. 95 2. 86% 212. 731 284. 113 2. 38 4. 17 Total loss factor [V/p. C] 0. 8111 (σ=4 mm) Cut off fre. (MHz) TE 11： 1126 TM 01： 1471 Ref： TESLA: Ep/Eacc=2, Bp/Eacc=4. 26 LL：Ep/Eacc=2. 38, Bp/Eacc=3. 65 4

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 5

HOM coupler design p Research target Cut off TE 11： 1126 MHz Cut off TM 01： 1471 MHz Beam stability: • HOM Qe~104 HOM power: • If beam spectrum coincide with HOM, the requirement for Qe should less than 103. (For TM 011, if resonance happen, Pt=300 W (Qe=103)) • Maximum power: 1 k. W • Dangerous monopole: aroud 1200 MHz • Dangerous dipole: 800 MHz~900 MHz, 1200 MHz HOM coupler bandwidth: 800~1400 MHz HOM damper: ＞ 1400 MHz 6

HOM coupler design HOM absorber bandwidth Frequency distribution of HOM power Higher-Order RF power (Watts) p 140 120 100 80 425 bunches per beam 0. 047 m. A av. in each bunch σz=2. 9 mm toal HOM power: 0. 465 k. W/cavity for f> 1. 47 GHz: 0. 383 k. W 60 40 HOM power spectrum (H-LP) 20 0 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940 RF frequency range (GHz) for comparison Q 0 losses: Ea=20 MV/m Q 0=1. 2 E+10 P=33. 5 W HOM absorber focus on 1 GHz~20 GHz. 7

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 8

Broadband HOM coupler TM 01 -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. 9

2 -cell cavity with couplers p Monopole mode damping results • use average current to calculate threshold • not include the frequency spread • For Z, 32 cavity used TM 020 TM 011 • • • Continue to optimize the broadband damping results Increase the probe head area Increase the insert depth 10

2 -cell cavity with couplers p Dipole mode damping results • use average current to calculate threshold • not include the frequency spread • For Z, 32 cavity used TE 111 TM 110 • • • Hybrid TM 111/ TE 121 Continue to optimize the broadband damping results Increase the probe head area Increase the insert depth 11

Optimized design of probe type TM 01 -TEM TE 11 -TEM Increase the area of the probe end: • The damping for TE 111 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. 12

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 13

cut off: TM 01 cut off: TE 11 1471 MHz 1126 MHz Loop coupler: increase the damping results for TE 111 14

HOM coupler position Face 1 h HOM coupler r=40 mm d=100 mm • • h=70 mm, power dissipated on face 1 is P 1=0. 157 m. W*16=2. 5 m. W When Q 0=2 E+10 Pc=12. 5 W The HOM coupler tube length is 70 mm. Angle between two HOM is 100 deg. 15

2 -cell cavity with couplers TM 110 TE 111 TM 020 TM 111/ Hybrid TE 121 TM 011 • • Beam parameters (wangdou 20160918) 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 TM 011 TM 110π/2 mode can not meet the requirement. • • For H design, the Qe for the TM 110 -π/2 mode can not meet the requirement. The damping for TE 111 mode is perfect. Not include the frequency spread 16

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

Outline p Cavity design p HOM coupler design • Broadband coupler • Loop coupler p Summary 20

Summary p 2 -cell design p HOM coupler RF design ü The damping for TE 111 mode is perfect ü The broadband damping results can meet the requirement p Next ü Thermal analysis ü Mechanical design ü …… 21