Low-Level RF of BEPCII

1. Low-Level RF of BEPCII Sun YI IMAC’07 May. 11, 2007 IHEP

2. Review the past one year • The Hardest and key time was from Apr.06 to Dec.06 • West LLRF was used for the horizontal test and the Q0 measurement at the test room; All the Q0, both East and West SCC, are higher than the design target. ( June~Sep. 2006) The first time on the high power test of SCC in China made a big challenge on the LLRF • LLRF installation、cabling、and calibration (Mar.~Oct. 2006) • Commissioning 2 stations of SRF ( Oct.~Nov. 2006 ) • The East station join in the beam commissioning ( Nov. 2006) • SR run with only East station ( Dec. 2006 ~ Feb. 2007) • West station was used for the e+ ring commissioning ( Feb. 2007) • Two stations have been used for physic collision run ( Apr. 2007)

3. During the past one year, 2 LLRF stations have been finished, installation、cabling、calibration、high power test and Q0 measurement、commissioning SRF, now e+/e- beam run perfectly.

4. God and the Double Interlock prevent SRF from damageHigh power INTL: cooling water & wind、temperature、Klystron & circulator, etc.LLRF INTL: quench、arc、RF power limitation、vacuum、 cryogenic、 tuner，etc. emergency LLRF interlock quench arc P+ P_

5. Calibration Vc by 3 methods • Determine Vc by RF forwarding power P+ R/Q=95.3QL≈2E+5 P+=13kw →Vc=1MV • Confirm Vc by RF field inside the SCC Q15D≈1.09E+11 P15D=90mw→ Vc=1MV • Calibration Vc by synchrotron oscillation frequency measured result: fs=22.3KHz at Vc=0.6MV

6. Beam and RF power matched in a typical SR run beam power=53kw P+=59kw 2.5GeV 150mA 1.33MV 22.5KW no beam P-=4kw Ramp 2.5GeV+WG

7. Vc oscillation result in the beam trip by LLRF RF voltage Vc beam RF forwarding power P+ • 60mA e- lost at Dec.4, 2006 • RF voltage recovered and the oscillation disappeared after the beam lost • Vc=0.6MV, the oscillation period=3ms • After adjusting the ALC feedback loop parameter, this problem was cured, the beam current can be increased to 200mA in Dec.2006 • This is not the Robinson instability, I still set the cavity frequency detune angle=0 degree till 200mA RF reflection power P_

8. First high power test of #2 SCC at June 06 • Apr 29~May 11 finished the room temperature RF aging to coupler 150KW • May 23 purify GHe • May 30 cold down SCC、June 7 LHe level=46%、June 13 level=95% • June 1~18 LLRF commissioning with Klytron、calibration RF power • June 19 LLRF test the frequency tuner and piezo for cavity • June 20 RF aging on the coupler 100kw、cavity detune at 4K temperature • June 21 quench protection test、tuning the cavity • June 22 detune±1KHz、±450、cavity frequency locked、measured QL=2.1E5 • June 23 first reached 1MV、calibration Vc、RF power、setting LLRF loops • June 24 1.2MV、measurement Q0=1×109 • June 25 LLRF test the RF pulse aging 、5 radiation sensors test OK • June 26 Sino-Japan confirmed the safty and the Vc calibration • June 27 1.55MV first quench happened • June 28 1.7MV、36.5KW、radiation 32mSv/hr • June 29 reached 2MV in the first time • June 30 RF pulse aging , at 2MV measurement Q0=5.4×108 • July 1 measureQ0 at 1.8MV、1.5MV、1.4MV、1.3MV • July 3 warm up the #2 SCC • July 11 #2 SCC reached room temperature

9. Using LHe consumption to measure Q0 • Function Vc—RF voltage PC—RF power consumed by the cavity wall Ptotalloss—the whole module heat loss under a Vc Pstaticloss—cryostat heat loss without RF field Pheater—the heater power inside the cryostat • Liquid Helium parameters: at 1.2bar、4.2K liquid Helium→Gas potential heat=19.4 KJ/Kg LHe proportion gravity = 122Kg/m3 after closing the input valve, LHe level will be reduced from 96% to 85% within a time LHe volume vs level = 2.73Liter/1% (roughly) with a given Vc, to determine the PC by the reducing of the LHe

10. First measurement of Q0 for #2SCCVc—over 2MV、heater=0w、LHe level=red 18:40 close valve,LHe level=98% RF voltage over 2MV 18:23 increasing LHe level RF power over 50KW 18:53 RF interlock at LHe level=85% cavity vacuum heater=0W

11. High power test and Q0 measurement

12. modulation pulse curve RF waveform by the pulse modulation cut off RF within 0.2ms as quench happened cavity frequency loop closed cavity frequency was disturbed by GHe pressure and others

13. RF pulse aging to increase the quench Vc and reduce the radiationbefore the aging: quench happened at 1.7MV, radiation 35mSv/hrafter RF aging: quench at 2MV, radiation=10mSv/hr at 1.7MV At 2MV，the radiation intensity maybe 300~500mSv/hr （over the meter range ） second pulse aging third pulse aging first pulse aging before RF pulse aging

14. Summary1) West LLRF finished the high power test for #2 & #1 SCC ( June~Sep.) at 2MV: Q0=5.8E8 (East SC) Q0=1E9 (West SC) Vacuum gate valves were not damaged by the dark current2) East LLRF joined in the beam run at Nov.2006 ( on time)3) East station was dedicated the SR run ( Dec.06~Feb.07) reached e- beam 160mA@2.5GeV ~64kw4) West station was put in the e+ ring commissioning ( Feb. 2007) reached e+ beam 150mA@1.89GeV ~18kw5) frf=499.8MHz±14KHz were shifted by 0.2KHz step without beam loss6) fs、φs、 Vc 、and RF power are matched7) RF power limitation at LLRF were released over 80KW ( Apr.2007 ) LLRF will be test under the heavy Beam loading in the future • Thanks to Prof. K. Akai , T. Furuya, S. Mitsunobufor help. • Thanks to Dr. Wang Chaoen of TLS , and Dr.Zhao zhentang of SSRF for the useful discussions. • Thanks to Prof. S. Kurokawa for pushing on the co-operation. Thanks every expert and colleague