CEPC 1.3GHz & 650MHz SC cavity high Q R&D Z.C. LIU #, P. Sha, H.J. Zheng, J.Y. Zhai, M.Y. Wang, G.W. Wang, Y. Sun, J. Gao

Contents Cavity requirement Cavity N doping Cavity experience Next step

CEPC cavity requirement Frequency: 650MHz Gradient: 15.5MV/m High Q 0 >4x10 HOMs power damping (several kilo watts) Low loss factor No trapped mode ParametersCEPC-Collider CEPC- Booster Cavity Type 650 MHz 5-cell Nitrogen-doped Nb 1.3 GHz 9-cell Nitrogen-doped Nb V cav / V RF 17.9 MV / 6.87 GeV20 MV / 5.12 GeV E acc (MV/m) Q0Q0 2K Cryomodule number 96 (4 cav. / module) 32 (8 cav. / module) RF coupler power / cav. (kW) 280 c.w.20 RF source number192 (800 kW / 2 cav.)256 (25 kW / cav.) HOM power / cav. (kW) HOM damper 2K + RT 2K + 80K

4 CEPC main ring cavity RF design parameters ParameterUnitMain Ring Cavity frequencyMHz650 Number of cells-5 Cavity effective lengthm1.154 Cavity iris diametermm156 Beam tube diametermm170 Cell-to-cell coupling-3 % R/QΩ514 Geometry factorΩ268 E peak /E acc -2.4 B peak /E acc mT/(MV/m)4.23 Cavity longitudinal loss factor k ∥ HOM * V/pC1.8 Cavity transverse loss factor k ⊥ * V/pC/m2.4 Acceptance gradientMV/m20 Acceptance Q 0 -4E10 * collider bunch length 2.65 mm

Fermilab 650 MHz single cell (beta=0.9) VT （ N-dopingVS. Standard post-process ） CEPC 主环腔垂测指标 CEPC 主环腔运行指标 PIP-II cavity Bpk/Eacc=3.75 CEPC cavity Bpk/Eacc = 4.2 Alexander Romanenko, FCC Week 2015

FNAL&JLAB1.3 GHz N-doping 9-cell cavity CEPC 增强器腔运行指标 Alexander Romanenko, FCC Week 2015

Benefit of N doping on 1.3GHz and 650MHz cavity Q 0 is increasing obviously The very high Q 0 of Nearly will dramatically reduce the RF loss of the cavity, lower the requirement for the cryogenic system Open a way to loss free cavity and the research of superconducting phenomenon.

Vertical Test Condition For N doped SC cavity: Tested at 2K Proper coupling factor Low magnetic field to lower the residual resistance Fast cool down is needed Clean assembly

Dan Gonnellay and Matthias Liepe, FLUX TRAPPING IN NITROGEN-DOPED AND 120C BAKED CAVITIES, Proceedings of IPAC2014, Dresden, Germany, WEPRI063 R res Vs. Magnetic field

R res Vs. Cool down rate Dan Gonnellay and Matthias Liepe, FLUX TRAPPING IN NITROGEN-DOPED AND 120C BAKED CAVITIES, Proceedings of IPAC2014, Dresden, Germany, WEPRI063

HPR, Vertical test for 1.3GHz cavity HPR leakage detecting Injection of Liquid He

Test results (before N-doping) , Vertical test before N-doping at IHEP. Quench at 17MV/m.

N-Doping of 1.3GHz Cavity , N-Doping + Plasma Cleaning at PKU Induction heating Chamber Maintain 10min （ 7.5E-4 Pa ） Heating to 800° (7min ） N-doping 10min （ 2.6 Pa ） Maintain 5min （ 8.5E-4 Pa ） Cool down

Doping data Nitrogen injection 10 minutes Hydrogen degas 10 minutes Nitrogen anneal 5 minutes

Vertical test after N-Doping , Vertical test after N-Doping No Q0 improvement.

Test results for 1.3GHz cavity at FNAL N-doping + EP

Doping data of JLAB FNAL 、 JLAB 、 Cornell: 60+ cavities have been N-doping treated, the same procedure with any minor changes of N 2 injection.

The reason N-doping parameters? (Temperature Vs time, Pressure VS time) Vertical test condition? Plasma cleaning worse than EP (foreign labs).

650MHz N-doping single cell cavity Beta=0.82

Leak check Coupling factor calibration Ready for VT test

650MHz beta=1 single cell cavity R/QGEpeak/EaccBpeak/Eacc 140Ω288Ω1.93.6mT/(MV/m) RF parameters E field M field 施加载荷约束条件 最大应力 /MPa 最大形变 /mmdf/dp 1.5atm 端口均约束 kHz/atm Hz/Torr 0.5atm atm 一端口自由 kHz/atm -475Hz/Torr 0.5atm

Shape distortion （ end fixed ， 1.5atm ） Force distortion （ end fixed ， 1.5atm ） 650MHz beta=1 single cell cavity

650MHz single-cell cavity (Beta=1) for CEPC

EP EP facility is under construction at Ningxia province, in cooperation with OSTEC.

Vacuum furnace at IHEP Chamber Diffusion Pump Valve

Chamber Diffusion pump MFC Valve N 2 injection (undergoing) N2N2

Cavity experience 650MHz beta=0.82 cavity 1.3GHz ILC cavity (J.Y. Zhai, TTC report)

Cavity experience 1.3GHz high current high HOMs damping cavity

650MHz SC VT The first 650MHz cavity reached the design value in China.

Next step Finish the 650MHz single cell cavity VT by the end of Sept. Establish the N- doping facility as soon as possible. Finish the N-doping procedure on the 650MHz cavity and VT by the end of this year.

Thanks!