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

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

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 Target Cryomodule Specification

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. 4

Cavity Fabrication and Qualification 5 Cavity #1 Cavity #2

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 6

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. 7

Input Coupler Conditioning 8 Vac 1 Vac 2 Vac 3

HOM Absorbers 9 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

TT2 Tile Removal & Cold Tests 10

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

Cavity String Assembly 12

Outer Cryomodule Assembly 13

Cavity String Integration 14

Final Cryomodule Configuration 15 3 Layers of Magnetic Shields

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. 16 COOL-IT New Cryomodule Existing Cryo-system for ALICE

17 ConceptDesignBuild Concept to Commissioning

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

TCF 502K BOX1500 L DewarLINACBOOSTER COOL-IT HEX COOL-IT Transfer Lines COOL-IT Integration on ALICE 19 Ready for Commissioning....

EMMA – Worlds 1 st NS-FFAG 20 Injection Line Diagnostics Beamline Frequency (nominal) 1.3 GHz No of RF cavities19 Repetition rate Hz Bunch charge16-32 pC single bunch Energy range10 – 20 MeV LatticeF/D Doublet Circumference16.57 m No of cells42 Normalised transverse acceptance 3 π mm-rad

EMMA Complete – Aug

RF System Requirements Voltage: – 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 22

The EMMA RF System 23 RF Cavities Waveguide Distribution System High Power RF Amplifier System Libera LLRF 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. 24

First High Power Commissioning Excellent cavity control stability (up to 40 kW so far): –0.007% rms voltage –0.027 o 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 /08/2010

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. 26

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. 27

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. 28 Synchrotron Oscillations Observed

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

EMMA Milestones Project start Apr 2007 Design phase Apr 2007 – Oct 2008 Major procurement contractsMay 2007 – Aug 2009 Off line build of modulesOct 2008 – 15 th Jun 2010 Installation in Accelerator HallMar Sep 2009 Test systems in Accelerator HallJul - Oct st Beam down the Injection line 26 th Mar st Beam through 4 sectors 22 nd Jun st Circulating beam in EMMA16 th Aug st Accelerated beam in EMMASep/Oct 2010 (Underway) ALICE & EMMA shutdownNov – Dec 2010 EMMA Experiments Jan 2010 – Mar 2011 Basic Technology Grant completeMar

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! 31

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. 32 Feed Forward Table

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 33

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 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. 34

Fabrication at Shakespeare 35

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 200 MHz Hope to be able to nurture UK industry to demonstrate complete SRF cavity fabrication capability within the next 3 years. 36