alice srf system commissioning experience

ALICE SRF SYSTEM COMMISSIONING EXPERIENCE

A. Wheelhouse

9th June 2009 ALICE SRF Systems Commissioning Experience A Wheelhouse

A. Wheelhouse

ASTeC, STFC Daresbury Laboratory

ERL 09

8th – 12th June 2009

ALICEAccelerators and Lasers In Combined Experiments

• Brief Description– ALICE– Superconducting RF Modules – RF Sources– RF Sources

• Cavity Commissioning Experience– Past and Present

• Operational Experience• Future Plans

– Short and Long Term

• Summary


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.

The ALICE Complex

Booster

LinacParameter Units

Nominal Gun Energy 350 keV

Injector Energy 8.35 MeV


Gun

Injector Energy 8.35 MeV

Circulating Beam Energy 35 MeV

RF Frequency 1.3 GHz

Bunch Repetition Rate 81.25 MHz

Nominal Bunch Charge 80 pC

Maximum Train Length 100 µS

Maximum Train Repetition Rate 20 Hz

Maximum Average Current 13 µA

SRF Modules• 2 x Stanford/Rossendorf

cryo-modules

– 1 Booster and 1 Main LINAC.

• Fabricated by ACCEL.

• Booster module:


• Booster module:

– 4 MV/m gradient.

– 52 kW RF power.

• Main LINAC module:

– 13.5 MV/m gradient.

– 13 kW RF power.

RF System Specifications

Booster ERL Linac

Cavity 1 Cavity 2 Cavity 1 Cavity 2

Gradient (MV/m) 5 3 13.5 13.5

Q 5 x 109 5 x 109 5 x 109 5 x 109


0.1ms bunch trains @ 20 Hz repetition rate

Qo 5 x 109 5 x 109 5 x 109 5 x 109

Qe 3 x 106 3 x 106 7 x 106 7 x 106

Power (kW) 32 20 6.7 6.7

Power Source 2 x e2v CPI e2v Thales

SRF Modules (Cont)


IOT RF Power SourcesCPI K51320W e2v IOT116LS Thales TH713

Parameters CPI e2v Thales UnitsParameters CPIK51320W

e2v IOT116LS

ThalesTH713

Units

Frequency 1.3 1.3 1.3 GHz

Max CW Power 30 16 20 kW

Gain 21 >20 20.9 dB

Beam Voltage 34 25 25 kV

Bandwidth 4.5 >4 >5 MHz

Efficiency 63.8 >60 60.4 %


Cavity Vertical Tests at DESY

Booster Cavity1 Linac Cavity1


● Specification

Jul – Dec 2005

Booster Cavity2 Linac Cavity2

High Power Tests

Booster Linac

Cavity 1 Cavity 2 Cavity 1 Cavity 2

Vertical Tests at DESY (Jul – Dec 2005)

Eacc (MV/m) 18.9 20.8 17.1 20.4

Qo 5 x 109 5 x 109 5 x 109 5 x 109


Module Acceptance Tests at Daresbury (May – Sept 2007)

Max Eacc (MV/m) 10.8 13.5 16.4 12.8

Qo

3.5 x 109 @

8.2 MV/m

1.3 x 109 @

11 MV/m

1.9 x 109 @

14.8 MV/m

7.0 x 109 @

9.8 MV/m

Limitation FE Quench FE Quench RF Power FE Quench

Booster Commissioning


Linac Commissioning


Predicted LLRF Electronics Lifetime at 9 MV/m


Further Cavity Conditioning

Booster

• Cavity 1– Eacc = 9.4 MV/m

– Conditioned for 7:10 hrs

• Cavity 2– E = 8.8 MV/m

Linac (+ 100mm lead wall)• Cavity 1

– Eacc = 10.7 MV/m– Conditioned for 10:50hrs

• Cavity 2– Eacc = 10.8 MV/m– Conditioned for 7:10 hrs

• Conditioning


– Eacc = 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

• 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 5mSv/h @ 9MV/m– Lifetime of LLRF electronics

> 10,000hrs

Further Booster Cavity Commissioning


Further Linac Cavity Commissioning


Operational Reliability Issues

• Investigations into accelerating gradients postponed– Numerous ancillary power supplier failures

• Grid, filament and ion pump supplies

• Single HVPS• 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


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 – 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


Isolation Window Failure

Booster Cavity 1


Window Failure Analysis


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


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

Booster Cavity Operation


Linac Cavity Operation


Beam Loading Issues• Initially beam loading seen at

6pC on Booster– Booster 1:

Qext 2.48x106 �5.20x105

– Booster 2:

Qext 2.61x106 �8.97x105 No beam loadingQext 2.61x10 �8.97x10

• Further beam loading– Train lengths > 50µS

– Bunch charges > 10pC

• Plans to improve LLRF feedback response times

• Optimisation of Qext

• Feed forward investigations


Beam loading

Energy Recovery – 20.8MeV


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


• 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

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

alice srf system commissioning experience

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