SRF and RF Activities

1. SRF and RF Activities Peter McIntosh STFC and Cockcroft Institute CI SAC Review 1 – 2 November 2010

2. Outline International Cryomodule COOL-IT Cryogenics EMMA RF System Digital LLRF Working with UK Industry Conclusions

3. 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

4. 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.

5. Cavity Fabrication and Qualification Cavity #1 Cavity #2

6. 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

7. 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.

8. Input Coupler Conditioning Vac 3 Vac 1 Vac 2

9. 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

10. TT2 Tile Removal & Cold Tests

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

12. Cavity String Assembly

13. Outer Cryomodule Assembly

14. Cavity String Integration

15. Final Cryomodule Configuration 3 Layers of Magnetic Shields

16. 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 COOL-IT Existing Cryo-system for ALICE

17. Concept to Commissioning Concept Design Build

18. COOL-IT Verification • Instrumentation & Controls developed in-house • Manufactured with the help Local UK industry • Off-line tests at the factory conducted successfully

19. COOL-IT Integration on ALICE 2K BOX 1500 L Dewar TCF 50 LINAC BOOSTER COOL-ITHEX COOL-IT Transfer Lines Ready for Commissioning....

20. EMMA – World’s 1st NS-FFAG Diagnostics Beamline Injection Line

21. EMMA Complete – Aug 2010

22. 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

23. The EMMA RF System Libera LLRF System RF Cavities High Power RF Amplifier System Waveguide Distribution System

24. 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.

25. 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

26. 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.

27. 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.

28. 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 Observed

29. 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.

30. 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

31. 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!

32. 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

33. 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

34. 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.

35. Fabrication at Shakespeare

36. 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.