Summary of RF Sessions Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory

1. Summary of RF Sessions Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory MICE Collaboration Meeting at CERN, Switzerland 25 February 2007 D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

2. Agenda 9:00 AM ~ 12:30 PM, Friday, 23 February 2007 (31-3-004) • 201 MHz RF system for MICE • by Peter CORLETT and Joe ORRETT (Daresbury Laboratory) • Design of the MICE RF Cavity Module • by S. VIROSTEK (LBNL) • MTA RF programs and progress • by Alan BROSS (FNAL) Coffee break • Refurbishment of CERN RF equipment • by Maurizio VRETENAR (CERN AB/RF) • Multifactoring Study Progress • by Rebecca SEVIOUR (Cockroft Institute) • Progress at RAL • by Chris NELSON (RAL) • Discussions D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

3. 201 MHz RF system for MICE What needs to be done? • Build up and demonstrate operation of the amplifiers needed to power the MICE RF cavities • 201 MHz at ~ 2.5MW • Two amplifier stages • Equipment loaned to MICE from LBNL (in various states of disrepair) Summary by P. Corlett • Most equipment for the Burle 4616 is in place • One old tube and two new ones • We are on track to test the 4616 system in June 2007 • Work on the TH116 systems will begin immediately after 4616 tests • This is where the hard work starts! • Major mechanical effort (4~6 months!) • Aim to test a complete amplifier chain late 2007 D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

4. MICE RF System Ready for tests! D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

5. Hardware photos of 4616 circuits • Solid state amplifier • Power supply • Rack is in place • Water circuits have been connected & tested • Old 4616 tube has been installed. • Two new tubes on site D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

6. LLRF for MICE Functions: • RF Drive • Amplitude Set/Control • Phase Set/Control • Pulse Control • Synchronisation Options • Rossendorf analogue system • AD9910 (new, not available yet) Conclusions by J. Orrett • The Rossendorf analogue LLRF system provides a proven RF control system. However it lacks the flexibility and potential for upgrading the AD9910 has. A sensible approach is to have the Rossendorf LLRF as a proven “fallback position” whilst evaluating the AD9910. The AD9910 is not yet commercially available but DL should be able to purchase evaluation boards in the near future Suggestions Possibility for using the same LLRF as CERN SNS LLRF (LBNL FPGA based system) D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

7. Design of the MICE RF Cavity Module by S. Virostek • RFCC module design status • Integration of MICE Cooling channel • Options for vacuum seal • Options for module joints D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

8. RFCC Module Design Status • Prototype 201 MHz cavity is at FermiLab awaiting high power RF testing with applied magnetic field. • Two 42 cm  curved Be windows have been fabricated by Brush Wellman. 3rd window is under way. • Coupling coil design is under way at ICST in Harbin. Details of ICST/LBNL collaboration are being worked out. • Base mounting scheme for RFCC and other MICE modules has been established by RAL. D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

9. ~36 Bolts Weld Lip Weld Metal Wire Seal or O-ring AFC Module RF Module Commercial Bellows Joint Seal Options • Long discussions: • O-rings vs metal seals • Summary on Pros and Cons (see S. Virostek’s talk) R&D program for seals? D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

10. MTA RF Progress by A. Bross D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

11. Chipmunk Plastic Scintillator 805 CsI 201 Magnet MTA Hall Instrumentation D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

12. Focus of the RF R&D • Study the limits on Accelerating Gradient in NCRF cavities in magnetic field • However • We believe that the behavior of RF systems in general can be accurately described (predicted) by • Tensile strength of the material(s) used in the cavity fabrication (T) • Local surface field enhancements (beq) Esurf = £ Ö(2T/eo)/beq • This applies to all accelerating structures • In SC structures local heating becomes problem first • Follows universal curve D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

13. Status and Plans • 805 MHz pillbox cavity test magnetic fields • Confirmed previous experimental results • Switch to button tests in a few weeks • 201 MHz cavity had run well before without magnetic field, but • Full RF power reflection, appears to be shorted • Low power measurement found no problem • The problem seemed to stem from the fact that parts from multiple vendors where used in the 4” coax run • Power coupler • Straight sections • Elbows • At the interfaces between parts from different vendors, the fit-up was not ideal • Inner conductor specifications seemed to vary • This has now been fixed • In addition we will be using pressurized (12 pisg) SF6 in the 4” coax run as the insulating gas instead of air D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

14. D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

15. Asymptotic Gradient limit line at 1.25 T 1.25 T Data RF Conditioning without Magnetic Field 2.5 T Data Latest Electric field limit Data at 2.5-T and 1.25-T in the LBNL Single Cell Cavity with Curve Be Windows coated with TiN • The Asymptotic limit line shown indicates the continuous Gradient sparking limit. In all the cases studied including Lab G this line as predicted the Gradient Limit for the cases under Study. • For the 1.25 T case the Save operating limit has been shown to be 20 MV/m D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

16. High Pressure H2 Filled Cavity WorkMuons Inc. • High Pressure Test Cell • Study breakdown properties of materials in H2 • Run in B field • No degradation in M.S.G. up to » 3.5T Gas filled Cavity D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

17. Refurbishment of CERN RF equipment for MICE M. Vretenar CERN AB/RF D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

18. CERN Linac1 amplifiers Developed in 1956-59. Photo taken in 1959 for the old Linac1 amplifier  Frequency 202.56 MHz, equipped with the TH170R triode, can deliver a maximum of 2.5 MW with an anode voltage of 40 kV, but near delivered for more than 1.7 MW. The tube is water cooled, and can operate at a maximum of 0.3% duty cycle. The unit is about 3.6 m high, 1m x 1m base. Only 2 units left, one was modified for 101 MHz and then 88 MHz (gradient test for bunch rotation cavities in NF), the other is a cannibalised spare, stored in a hall for 50 years. D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

19. Caveats • The refurbishment of the linac amplifiers for MICE has been authorized by the AB Department (Nov. 06), but there are still some doubts concerning the level of UK support to CLIC… • The CERN Linac RF team is heavily involved in Linac4 and from next year will work 100% on this project  it is now or never, this year we still have a window for at least starting refurbishing the amplifiers, from next year it will be very difficult. D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

20. Organisation of work • Principle: the reconstruction is done at CERN, up to the testing of filament. Then, the amplifier is transferred to RAL or Daresbury for the RF tests. • At CERN: • Collect drawings, and design modified parts. • Make inventory of existing and missing parts. • Machine mechanical parts. • Dismount, clean, reconstruct amplifiers. • Assemble ventilation circuitry. • Assemble filament circuit and filament regulation (PLC based, CERN standard) • Test filament and ventilation • These activities can be realized with minimum support of CERN staff if temporary labor is used for: draftsman/designer, mechanic, wireman. • At MICE: • Install cathode switch circuit (eventually also HOM suppressors). • Connect HV and RF loads. • Test with RF power. Suggestions: involvement of MICE people D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)

21. Summary • 201 MHz RF system (DL and CERN) • RF R&D with magnetic fields at FNAL • 805 MHz button tests • 201 MHz cavity conditioning • Multipactoring studies • RFCC module integration • Progress at RAL by Chris NELSON was not covered here, but can be found at MICE web site soon. Lots progresses in • Decay solenoid • Beamline • Presented with 5o+ photos • … • No plan for MICE cavity yet • Pending issues: cavity amplitude and phase measurement and stability • A joint session with DAQ group future D. Li – RF Session Summary at CM17, CERN, Switzerland (25 February 2007)