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SRF and RF Activities. Peter McIntosh STFC and Cockcroft Institute CI SAC Review 1 – 2 November 2010. Outline. International Cryomodule COOL-IT Cryogenics EMMA RF System Digital LLRF Working with UK Industry Conclusions. International ERL CM Collaboration.

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srf and rf activities

SRF and RF Activities

Peter McIntosh

STFC and Cockcroft Institute

CI SAC Review

1 – 2 November 2010


International Cryomodule

COOL-IT Cryogenics

EMMA RF System

Digital LLRF

Working with UK Industry


international erl cm collaboration
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

srf cavity design
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.
cavity processing
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
input coupler design
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.
hom absorbers
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 through

Cornell injector cryomodule

tuner development
Tuner Development
  • Employed a modified Saclay-II tuner assembly:
    • Wider aperture
    • Low voltage piezo cartridges
  • Dual cams precision aligned and pinned.


Modified Saclay-II

final cryomodule configuration
Final Cryomodule Configuration

3 Layers of

Magnetic Shields

system to cool to i ntermediate t emperatures
System to COOL to Intermediate Temperatures
  • The radiation shields and other thermal intercepts in the existing ALICE SRF Cryomoduleare cooled with LN2.
  • The boiling of liquid nitrogen generates microphonics which detune and destabilise the operating frequency.
  • The new cryomodulewill 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 .

New Cryomodule


Existing Cryo-system for ALICE

concept to commissioning
Concept to Commissioning




cool it verification
COOL-IT Verification
  • Instrumentation & Controls developed in-house
  • Manufactured with the help Local UK industry
  • Off-line tests at the factory conducted successfully
cool it integration on alice
COOL-IT Integration on ALICE


1500 L Dewar

TCF 50




COOL-IT Transfer Lines

Ready for Commissioning....

emma world s 1 st ns ffag
EMMA – World’s 1st NS-FFAG

Diagnostics Beamline

Injection Line

rf system requirements
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
the emma rf system
The EMMA RF System

Libera LLRF System

RF Cavities

High Power RF Amplifier System

Waveguide Distribution System

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.
first high power commissioning
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.


emma frequency tuning
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.
emma synchronisation
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.
beam with rf
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 Oscillations


beam commissioning
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.
emma milestones
EMMA Milestones

Project start Apr 2007

Design phase Apr 2007 – Oct 2008

Major procurement contracts May 2007 – Aug 2009

Off line build of modules Oct 2008 – 15th Jun 2010

Installation in Accelerator Hall Mar 2009 - Sep 2009

Test systems in Accelerator Hall Jul - Oct 2009

1st Beam down the Injection line 26th Mar 2010

1st Beam through 4 sectors 22nd Jun 2010

1st Circulating beam in EMMA 16th Aug 2010

1st Accelerated beam in EMMA Sep/Oct 2010 (Underway)

ALICE & EMMA shutdown Nov – Dec 2010

EMMA Experiments Jan 2010 – Mar 2011

Basic Technology Grant complete Mar 2011

digital llrf developments
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!
operational performance
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

digital piezo tuner control
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
working with uk industry
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.
  • 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.