Download - Peter McIntosh STFC and Cockcroft Institute CI SAC Review 1 – 2 November 2010 SRF and RF Activities
Peter McIntoshSTFC and Cockcroft Institute
CI SAC Review1 – 2 November 2010
SRF and RF Activities
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Outline
• International Cryomodule• COOL-IT Cryogenics• EMMA RF System• Digital LLRF• Working with UK Industry• Conclusions
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International ERL CM Collaboration
• International collaboration initiated in early 2006:– ASTeC (STFC)– Cornell University– DESY– FZD-Rossendorf– LBNL– Stanford University– TRIUMF
• Fabricate new cryomodule and validate with beam.
• Dimensioned to fit on ALICE:– Same CM footprint– Same cryo/RF interconnects
• Scheduled for installation in April 2011
Target Cryomodule Specification
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SRF Cavity Design• 2 x 7-cell superstructure
cavities provided by DESY.• End groups re-designed by
LBNL, ASTeC and Cornell:– large b-p HOM absorbers,– larger variable coupler.
• Modifications performed and validated by Cornell.
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Cavity Fabrication and Qualification
1.0E+09
1.0E+10
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0
Qo
Eacc (MV/m)
Before He vessel weldingAfter He vessel welding
ALICE OperationalTarget
Design Target
1.0E+09
1.0E+10
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Qo
Eacc (MV/m)
Before He vessel welding
After He vessel weldingDesign Target
ALICE OperationalTarget
Cavity #1
Cavity #2
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Cavity Processing
• Cavity #1– 21/8/09
• 15µm BCP, HPR and 48hr 110C bake
– 25/9/09• 25µm BCP and HPR
– 8/3/10• 340µm BCP, HPR,
5µm micro-BCP and 48hr 115C bake
– 6/5/10• He vessel weld and
HPR
• Cavity #2– 6/12/09
• 80µm BCP and HPR– 21/1/10
• 80µm BCP, HPR and 15-20µm micro-BCP
– 12/3/10• 48hr bake at 115C
– 26/3/10• 320µm BCP and HPR
– 15/7/10• He vessel weld and
HPR
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Input Coupler Design• Utilised Cornell ERL injector
coupler as original design.• Cold section of the Cornell
injector coupler too long to load into the cryomodule.
• Removed 80 K intercept ring and two bellows convolutions.
• Reduced the 2 K to 5 K transition tube.
• Shortened the coupler cold section by 15 mm and modified 80K skeleton to allow cavity string insertion.
Original
Modified80K Intercept
removed
2K5K
80K 300K
Cold section shortened by
15mm
Original
Modified80K Intercept
removed
2K5K
80K 300K
Cold section shortened by
15mm
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Input Coupler Conditioning
Vac 1
Vac 2
Vac 3
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HOM Absorbers• Cornell ERL injector HOM absorber
utilised for high current operation (up to 100mA).
• Experience at Cornell however has identified that TT2 ferrite bulk resistivity increases considerably at T<80K, resulting in significant charge build-up. • Net effect is to
deflect and distort beam at low energy.
• Modification to remove TT2 ferrite tiles and rely solely on ceramic tiles to damp HOM power.
Beamlet distortion throughCornell injector cryomodule
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TT2 Tile Removal & Cold Tests
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Tuner Development
• Employed a modified Saclay-II tuner assembly:– Wider aperture– Low voltage piezo cartridges
Saclay-II
Modified Saclay-II
• Dual cams precision aligned and pinned.
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Cavity String Assembly
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Outer Cryomodule Assembly
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Cavity String Integration
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Final Cryomodule Configuration
3 Layers of Magnetic Shields
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System to COOL to Intermediate Temperatures
• The radiation shields and other thermal intercepts in the existing ALICE SRF Cryomodule are cooled with LN2.
• The boiling of liquid nitrogen generates microphonics which detune and destabilise the operating frequency.
• The new cryomodule will use Cold Ghe for cooling radiation shields and other thermal intercepts to avoid microphonic generation as there is no boiling.
• COOL-IT, developed indigenously by ASTeC, provides the necessary cooling power at intermediate temperatures at 80K and 5K .
COOL-IT
New Cryomodule
Existing Cryo-system for ALICE
17Concept Design Build
Concept to Commissioning
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• Instrumentation & Controls developed in-house• Manufactured with the help Local UK industry • Off-line tests at the factory conducted successfully
COOL-IT Verification
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TCF 502K BOX 1500 L Dewar LINACBOOSTER
COOL-IT
HEX
COOL-IT
Transfer Lines
COOL-IT Integration on ALICE
Ready for Commissioning....
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EMMA – World’s 1st NS-FFAG
Injection Line
Diagnostics Beamline
Frequency (nominal)
1.3 GHz
No of RF cavities
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Repetition rate 1 - 20 Hz
Bunch charge 16-32 pC single bunch
Energy range 10 – 20 MeV
Lattice F/D Doublet
Circumference 16.57 m
No of cells 42
Normalised transverse acceptance
3π mm-rad
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EMMA Complete – Aug 2010
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RF System Requirements
• Voltage:– 20 - 120 kV/cavity essential for serpentine
acceleration, based on 19 cavities– Upgrade possible to 180k
• Frequency:– 1.3 GHz, compact and matches the ALICE RF
system– Range requirement 5.6 MHz
• Cavity phase:– Remote and individual control of the cavity
phases is essential – 19 waveguide phase shifters
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The EMMA RF SystemRF Cavities
Waveguide Distribution System
High Power RF Amplifier System
Libera LLRF System
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EMMA LLRF System• Instrumentation
Technologies Libera LLRF system provides:– Initial cavity setting
conditions
– Precise control of the cavity amplitude and phase to ensure stable acceleration
• Diagnostic monitoring:– Cavity pick-up loops
– Forward and reverse power monitoring to each cavity
– IOT power levels before and after the circulator
• Novel synchronisation of the accelerators:– A 200µs beam pre-trigger
used to reset LLRF phase accumulators every beam pulse.
– The LLRF synchronises itself on every trigger pulse, preserves the relationship between ALICE 1.3 GHz and EMMA offset frequency.
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First High Power Commissioning• Excellent cavity control stability
(up to 40 kW so far):– 0.007% rms voltage– 0.027o phase
• Many issues with tuner and phase shifter motors, communication errors, slipping motor shafts etc.
• Ability to ‘ignore’ bad cavities from the GVS.
• Further work planned during shutdown to understand and fix all motor problems.
• Libera LLRF will then take full system control with updated control software.
17/08/2010
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EMMA Frequency Tuning
• Changing cavity frequency takes – 30 minutes.
• Currently using EPICS system to move motors in open loop.
• Using centre frequency and bandwidth controls ‘sweep analysis’ locates resonance of each cavity in system.
• A new centre frequency can then be set and the tuner motors driven.
• Calc detune shows new resonance of cavity.
• Low reflected power response used to fine tune each cavity.
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EMMA Synchronisation• Yellow = ALICE 1300GHz• Blue = EMMA 1301Ghz• Trigger on laser pre
injection pulse.• Measured on 12GHz
scope while varying GVS phase and amplitude:– Can see that the global
phase of EMMA being moved while maintaining lock during this simple test.
– Beam based analysis of the synchronisation will be demonstrated soon.
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Beam with RF• RF cavity phase set to 154
degrees separation (ToF).• Result on RF voltage on beam
is half of expected change in ToF:– Cavity phases not set
optimally.• RF buckets around transition
momentum still separated – not enough voltage for serpentine acceleration.
• Seen RF bucket & synchrotron oscillations inside it.
• Next step adjust each cavity phase separately use beam as diagnostic.
Synchrotron OscillationsObserved
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Beam Commissioning• Zero cross of each cavity to
find optimum phase angle.• During recent experiment
beam loading effects could be seen on Libera LLRF.
• Possibility to zero cross each cavity, tune for max acceleration - needs testing.
• Close loop on Libera system and find the correct phase – phase accumulator reset during sweep.
• RF acceleration essential goal before shutdown in Nov - Dec 2010.
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EMMA Milestones
Project start Apr 2007Design phase Apr 2007 – Oct 2008Major procurement contracts May 2007 – Aug 2009Off line build of modules Oct 2008 – 15th Jun 2010Installation in Accelerator Hall Mar 2009 - Sep 2009Test systems in Accelerator Hall Jul - Oct 20091st Beam down the Injection line 26th Mar 20101st Beam through 4 sectors 22nd Jun 20101st Circulating beam in EMMA 16th Aug 20101st Accelerated beam in EMMA Sep/Oct 2010
(Underway)ALICE & EMMA shutdown Nov – Dec 2010EMMA Experiments Jan 2010 – Mar 2011Basic Technology Grant complete Mar 2011
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Digital LLRF Developments• The LLRF4 board (developed
by Larry Doolittle at LBNL) is used as the basis for the design.
• FPGA software has been written using VHDL, Matlab and simulink.
• Supervision and control of the system is performed by a Labview VI, which also implements adaptive feed forward for beam-loading compensation.
• Labview system interfaces with the ALICE EPICS control system.
• System developed and implemented in < 18 months!
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Operational Performance• The Digital LLRF system has
been operated on the ALICE NC buncher cavity for a period of 2 weeks.
• The system was set up and locked within 10 minutes:– Short term stability better than the
existing analogue system (better than 0.04 degrees rms phase error)
– Long term stability is limited by temperature drifts within the analogue front end
– Some non linear behaviour has been observed
• The Adaptive feedforward system has been operated with beam.
• Found to be an effective way of reducing beam loading effects.
Feed Forward Table
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Digital Piezo Tuner Control• SRF cavities experience strong detuning during pulsed operation
due to Lorenz forces, causing the cavity to dynamically detune during the pulse.
• Detuning causes the LLRF system to work harder and increases RMS phase and amplitude errors.
• Piezo tuners can be used to dynamically apply tuning forces to the cavity within a pulse. Hence reducing the detuning problem
• A National Instruments controller has been sourced which provides :– 16 Bit I/O channels running at 100kHz– An FPGA on which control loops will run
• Programming is done within the Labview environment, reducing development costs.
• Development is at an early stage.• Hardware specified / designed• Hardware purchased• Programming has not yet begun
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Working with UK Industry• STFC Innovations (Mini-IPS)
funded activity with Shakespeare Engineering to fabricate a single-cell 1.3 GHz validation structure.
• Fabricated by Shakespeare and using STFC SRF processing and testing facilities to validate:– ISO 4/5/6 Cleanrooms– BCP chemical polishing– HPR rinsing– Vertical testing
• Validation by end Oct 2010.• First bulk Nb SRF cavity to
have ever been fabricated in the UK.
• Full IPS proposal now issued to build a 9-cell SRF cavity.
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Fabrication at Shakespeare
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Conclusions• All hardware for our international cryomodule is now
available:– Full integration and assembly preparations are underway.
• The new COOL-IT cryo-system has been verified and installed and is ready for commissioning when new cryomodule is installed.
• EMMA RF system has been successfully demonstrated – eagerly awaiting acceleration verification.
• Made outstanding progress in developing and implementing digital LLRF solutions:– other applications looming – MICE RF @ 200 MHz
• Hope to be able to nurture UK industry to demonstrate complete SRF cavity fabrication capability within the next 3 years.