Commissioning of the ALICE SRF Systems at Daresbury Laboratory Alan Wheelhouse, ASTeC, STFC Daresbury Laboratory ESLS RF 1 st 2 nd October 2008

Transcription

1 Commissioning of the ALICE SRF Systems at Daresbury Laboratory Alan Wheelhouse, ASTeC, STFC Daresbury Laboratory ESLS RF 1 st 2 nd October 2008

2 Overview ALICE (Accelerators and Lasers In Combined Experiments) Construction Status Commissioning Status RF System SRF Module Commissioning Status and Plans Summary

3 Technical Priorities for the ERL Prototype Operate a superconducting linac. Produce and maintain bright electron bunches from a photo-injector. Produce short electron bunches from a compressor. Demonstrate energy recovery. Demonstrate energy recovery (with an insertion device that significantly disrupts the electron beam). Have an FEL activity that is suitable for the synchronisation needs. Produce simultaneous photon pulses from a laser and a photon source of the ERL Prototype that are synchronised at or below the 1 ps level.

4 The ALICE Complex

5 Construction Status Photo-injector laser operating since April 06. Superconducting modules installed (July 06). Gun installed with a dedicated gun diagnostic beamline (Aug 06). First beam achieved from photocathode (Aug 06). Beam transport system installed and under vacuum (Feb 07). Cryo-system installed and used to cool accelerating modules down to 2K (May 07). SRF modules validated to high power (Sept 07).

6 Accelerator Installation

7 Gun Assembly Cathode ball Stem Cathode SF6 Vessel removed Electrons laser XHV Ceramic Anode Plate JLab design GaAs cathode. 500 kv DC supply. Transverse emittance ~3 mm mrad. Power supply commissioned 05. Ceramic delivered March 06. Spare ceramic delivered Nov 06.

8 Ceramic, Cathode Ball and Gun

9 Gun Commissioning Status Electron gun operated July and August 06. First beam from the gun recorded at 01:08 on Wednesday 16th August 06 with the gun operating at 250 kv Encouraging results obtained. Physical problems Voltage breakdown issues Field emission issues Vacuum leaks at brazed joints, valves or vacuum flanges Current leakage along the ceramic surface due to contamination from braze particles Presently the gun is being prepared for commissioning using a ceramic with a lower voltage capability

10 First Beam! 01:08 AM on Wednesday 16th August 06

11 Performance Achieved To Date Beam energy 350 kev (spec value) Bunch charge 22 pc (ultimate target 80 pc) Quantum efficiency Measured in the gun 1.2 %, Measured in the lab 3.5 % (ultimate target ~ up to 10 %) Bunch train length 6 ps pulse at 100 µs (spec value) Train repetition rate 20 Hz (spec value)

12 SRF Modules 2 x Stanford/Rossendorf cryo-modules 1 Booster and 1 Main LINAC. Fabricated by ACCEL. Booster module: 4 MV/m gradient. 52 kw RF power. Main LINAC module: 13.5 MV/m gradient. 13 kw RF power.

13 SRF Modules (Cont) JLab HOM coupler feedthrough design adopted for the LINAC module: Sapphire loaded ceramic. Higher power handling capability.

14 SRF Modules (Cont)

15 IOT RF Power Sources e2v IOT116LS CPI CHK51320W Thales TH713 e2v CPI Thales Frequency (GHz) Max CW Power (kw) Gain (db) > Beam Voltage (kv) Bandwidth (MHz) >4 4.5 >5 Efficiency (%) >

16 RF System Specifications Booster ERL Linac Cav1 Cav2 Cav1 Cav2 Gradient (MV/m) Q o 5 x x x x Q e 3 x x x x 10 6 Power (kw) Power Source 2 x e2v CPI e2v Thales 0.1ms bunch 20 Hz repetition rate

17 Cavity Vertical Tests at DESY Booster Cavity1 Linac Cavity1 Booster Cavity2 Linac Cavity2 Specification Jul Dec 2005

18 Cryo-system Operation Partial system procured from Linde. 4 K commissioning completed May 06. SRF Module delivery April and July 06. Problems with excessive system heat leaks and heater failure. Cryo specification 118 W at 2 K with 1 mbar stability. Actually achieved 118 W at 2 K with ± 0.03 mbar stability in May 07. Measured 5 W static load for both modules (i.e. ~2.5 W each) Specification < 15 W per module! System has operated successfully at 1.8 K with poor stability.

19 High Power Tests Vertical Tests at DESY (Jul Dec 2005) Booster Linac Cavity 1 Cavity 2 Cavity 1 Cavity 2 E acc (MV/m) Q o 5 x x x x 10 9 Module Acceptance Tests at Daresbury (May Sept 2007) Max E acc (MV/m) Q o x MV/m 1.3 x MV/m 1.9 x MV/m 7.0 x MV/m Limitation FE Quench FE Quench RF Power FE Quench

20 Cavity Processing (Linac Cav1) 15 Gradient (MV/m) Radiation (msv/hr) Gradient (MV/m) Vacuum (Torr) 1.0E-04 Gradient (MV/m) Radiation (msv/hr) Gradient (MV/m) E E-06 Coupler Vacuum (Torr) /09/ :50: /09/ :48: /09/ :45: /09/ :43: Date/Time 0 1.0E-07 11/09/ :50: /09/ :48: /09/ :45: /09/ :43: Date/Time Gradient (MV/m) and Warm Window Temperature (DegC) Gradient (MV/m) Coupler Warm (DegC) Coupler Cold (DegK) Cold Window Temperature (DegK) /09/ :50: /09/ :48: /09/ :45: /09/ :43: Date/Time

21 Coupler Heating (Linac Cav2) K temp cold window Gradient (MV/m) C temp warm window Gradient (MV/m) Cold Window Temp (degk) Warm Window Temp (degc) Temperature (degk and degc)

22 Booster Commissioning

23 Linac Commissioning

24 Predicted LLRF Electronics Lifetime at 9 MV/m

25 Further Cavity Conditioning Booster Cavity 1 E acc = 9.4 MV/m Conditioned for 7:10 hrs Cavity 2 E acc = 8.8 MV/m Conditioned for 7:30 hrs Conditioning 18mS pulse width at 10Hz Some CW conditioning at low power levels Linac (with lead wall) Cavity 1 E acc = 10.7 MV/m Conditioned for 5:30 + 5:50 + 4:30 Total 10:50hrs Cavity 2 E acc = 10.8 MV/m Conditioned for 7:10 hrs Conditioning 18mS pulse width at 10Hz Some conditioning at narrower pulse widths 1.6mS

26 Further Booster Cavity 1 Commissioning /5/08 8/5/08 9/5/ :57 17:02 17:05 17:08 17:15 17:17 17:22 12:03 12:12 12:30 12:35 13:06 13:22 13:30 14:43 14:54 15:56 16:02 16:06 16:10 12:53 13:18 13:24 Time Eacc (MV/m) X-ray spike Warm window trip Cold window trip Warm window trip Quench Nearing Quench Warm window trip Quench

27 Further Booster Cavity 2 Commissioning /5/08 8/5/ /5/08 10/5/ :53 17:14 17:15 17:16 17:17 17:19 17:22 10:31 11:57 12:53 13:06 13:18 13:22 13:24 13:30 13:33 14:43 14:50 14:50 11:53 12:02 12:09 12:14 12:45 12:59 13:23 14:26 14:39 14:52 15:13 15:27 15:34 15:44 Time Eacc (MV/m) Warm window trip Quench Quench Warm window trip

28 Further Linac Cavity 1 Commissioning /7/08 3/7/ / Eacc :13 18:24 18:47 19:17 19:37 19:49 20:19 20:35 20:51 21:06 21:17 21:26 19:02 19:33 19:57 20:59 21:15 20:25 21:08 21:33 21:49 Eacc (MV/m) Radiation (usv/hr) Warm window trip Fixed Unit On Wall by Blue Door (ai00) Isolation vacuum Quench Quench Quench Quench Quench Quench Rack of Linac Low Level Controls (ai03) 10 Upstream End of Linac SRF Module (ai01) 1 0 Time

29 Further Linac Cavity 2 Commissioning /7/08 11/7/08 14/7/08 16/7/ Eacc :03 18:38 19:25 19:47 19:57 20:24 21:00 12:34 13:12 13:34 14:10 14:24 14:40 15:07 15:16 15:32 15:49 16:08 17:23 09:03 10:00 13:04 13:32 14:09 Eacc (MV/m) Radiation (usv/hr) Isolation vacuum Quench Pressure rising Pressure rising Quench Quench 10 Fixed Unit On Wall by Blue Door (ai00) Rack of Linac Low Level Controls (ai03) Upstream End of Linac SRF Module (ai01) 1 0 Time

30 Power Supply Testing Failure of auxiliary power supplies during system trips Extensive crowbar testing of the HV system Issue mainly due to the inductance in the long lengths of HV cable Earthing issue discovered Resolved by referencing the return paths for each of the auxiliary power supplies at the power supply

31 Commissioning Status Very high levels of field emission High radiation levels reduced by lead wall around Linac Gradients less for Booster - No lead required Auxiliary power supply failures Cable re-wiring proof tested through comprehensive crowbar testing All IOTs powered into dummy loads at the same time Reduction in performance between the vertical tests and when they are installed in ALICE Further cavity conditioning commencing

32 ALICE Plans and Schedule 2008: Gun commissioning mid Oct Beam through booster end Oct Beam through the linac early Dec 2009: Beam through booster, linac and arcs end Feb Energy recovery demonstrated end Mar Longer term: Exploit THz radiation from compressor Compton backscatter phase 1 Install wiggler Energy recovery from FEL-disrupted beam Produce output from the FEL

33 Summary Gun conditioning Numerous issues Conditioning commencing with a lower voltage gun SRF Module Commissioning Gradient reduction seen High field emission levels Limited by a lead wall Conditioning commencing