ALICE SRF SYSTEM COMMISSIONING EXPERIENCE A. Wheelhouse ASTeC, STFC Daresbury Laboratory

Transcription

1 ALICE SRF SYSTEM COMMISSIONING EXPERIENCE A. Wheelhouse ASTeC, STFC Daresbury Laboratory ERL 09 8 th 12 th June 2009

2 ALICE Accelerators and Lasers In Combined Experiments Brief Description ALICE Superconducting RF Modules RF Sources Cavity Commissioning Experience Past and Present Operational Experience Future Plans Short and Long Term Summary

3 Technical Priorities for ALICE Operation of a superconducting linac module. 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 a 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 Booster Gun Linac Parameter Units Nominal Gun Energy 350 kev Injector Energy 8.35 MeV Circulating Beam Energy 35 MeV RF Frequency 1.3 GHz Bunch Repetition Rate MHz Nominal Bunch Charge 80 pc Maximum Train Length 100 µs Maximum Train Repetition Rate 20 Hz Maximum Average Current 13 µa

5 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.

6 RF System Specifications Booster ERL Linac Cavity 1 Cavity 2 Cavity 1 Cavity 2 Gradient (MV/m) Q o 5 x x x x 10 9 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

7 SRF Modules (Cont)

8 IOT RF Power Sources CPI K51320W e2v IOT116LS Thales TH713 Parameters CPI e2v Thales Units K51320W IOT116LS TH713 Frequency GHz Max CW Power kw Gain 21 > db Beam Voltage kv Bandwidth 4.5 >4 >5 MHz Efficiency 63.8 > %

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

10 High Power Tests Booster Linac Cavity 1 Cavity 2 Cavity 1 Cavity 2 Vertical Tests at DESY (Jul Dec 2005) 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) x x x x 10 Q o 8.2 MV/m 11 MV/m 14.8 MV/m 9.8 MV/m Limitation FE Quench FE Quench RF Power FE Quench

11 Booster Commissioning

12 Linac Commissioning

13 Predicted LLRF Electronics Lifetime at 9 MV/m

14 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. Isolation vacuum events at around 1.5kW Linac (+ 100mm lead wall) Cavity 1 E acc = 10.7 MV/m Conditioned for 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 Isolation vacuum events at around 1.5kW Radiation level reduced to 9MV/m Lifetime of LLRF electronics > 10,000hrs

15 Further Booster Cavity Commissioning

16 Further Linac Cavity Commissioning

17 Operational Reliability Issues Investigations into accelerating gradients postponed Numerous ancillary power supplier failures Grid, filament and ion pump supplies Single HVPS Stored energy issues under fault conditions due to long HV cable runs (~60m) Various types of IOTs had different requirements Filament settings Ion pump reference (cathode and body) Wiring not standardised

18 Power Supply Testing Extensive crowbar testing of the HV system Individual IOTs and complete system Earthing issue discovered Reliable operation with Grid and heater supplies referenced at the HVPS Spare HV cable along with ultra fast diodes used to control energy discharge In house grid supplies were installed Improved output isolation to protect against reverse voltages Grid protection diodes added at the power supply and IOT Spark gaps added between cathode and grid at the IOT

19 Isolation Window Failure Booster Cavity 1

20 Window Failure Analysis

21 Inspection And Clean Up Process Booster fully inspected and cleaned No obvious failure mechanism discovered Failure similar to one at Rossendorf CW Arc marks noted on inner and outer conductor Isolation vacuum events seen at low RF power levels - ~1.5kW Linac inspected Improvements made to isolation vacuum interlocks Broadband RF detectors added to the reflected power monitoring

22 Booster Cavity Operation

23 Linac Cavity Operation

24 Beam Loading Issues Initially beam loading seen at 6pC on Booster Booster 1: Q ext 2.48x x10 5 Booster 2: Q x10 5 ext 2.61x10 Further beam loading Train lengths > 50µS Bunch charges > 10pC Plans to improve LLRF feedback response times Optimisation of Q ext Feed forward investigations No beam loading Beam loading

25 Energy Recovery 20.8MeV

26 Future Plans Short Term Cavity commissioning for ALICE operation Analysis of quench points External Qs to be adjusted for 80pC operations Investigation of LLRF limitations Improvement to response times of feedback loops Feed forward Long Term Installation of a new 7-cell cryomodule Resolve high levels of field emission induced radiation

27 Summary Life of LLRF electronics extended by 100mm lead wall Reliability of HVPS and ancillary systems improved RF protection systems improved Energy Recovery achieved Beam loading seen for long pulse trains and high bunch charges Investigations on going