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RF systems for MICE Andrew Moss

NVEC 2014. RF systems for MICE Andrew Moss. The MICE RF Group and the TIARA WP7 Team Contributions include Daresbury , RAL, CERN, LBNL, LANL, FNAL, Strathclyde & Sheffield Universities, and Imperial College. Contents. The amplifier system for MICE

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RF systems for MICE Andrew Moss

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  1. NVEC 2014 RF systems for MICEAndrew Moss The MICE RF Group and the TIARA WP7 Team Contributions include Daresbury, RAL, CERN, LBNL, LANL, FNAL, Strathclyde & Sheffield Universities, and Imperial College

  2. Contents • The amplifier system for MICE • Modernisation and recommissioning of amplifier systems • Operation of the amplifier systems towards achieving high power operation

  3. The amplifier chain At Lawrence Berkeley National Laboratory (LBNL) there existed some amplifier systems from the Bevelac last used ~1992 201MHz tetrode and triode systems capable of up to 2MW pulsed operation

  4. Input cavity Cavity Socket Amplifier cavity Cavity 4616 super power tetrode Tube Output tuning stub

  5. 4616 Tetrode testing 60db directional coupler Starting at 10kV Grid one 250V Grid two 1800v 1kW drive 1mSec 1Hz pulsed operation Ideal 50 Ohm load 200kW CW water load 4616 data sheet

  6. Tetrode testing The tetrode has adjustments for cavity frequency, output coupling and input frequency tuning, all of which effect each other Initial setup using an old tube to check that all systems were ok, 100kW achieved With new tube fitted and conditioned we were able to optimise the output up to 234kW at 1Hz 1mSec pulse operation with good gain and electrical conversion

  7. Triode HT tank HT input Tuning stubs Water input with steam output Triode socket in HT tank

  8. Heater terminal Anode Tap Ad hoc and undocumented modifications had been made to improve the operation of the systems Considerable reverse engineering and revision was required Grid RF capacitor

  9. RF capacitor & resistor stacks 1 metre long cooled with compressed air RF input and movable Grid tap

  10. Parts ready for rebuild

  11. The re-build process With the amplifier completely stripped down we were able to inspect all the components Change from grid modulated to cathode modulated operation All the spring fingers needed to be replaced as these are key to the operation of the amplifier system Many of the sections of the amplifier were silver plated to improve the surface condition of the parts Motorisation of the operation of the tuning sections, grid tap and anode tap which tune the performance of the amplifier system

  12. HT blocking capacitor Anode section Grid section with RF input Moveable coax sections inside the amplifier structure

  13. HT tank under modification HT input to tank had become distorted Reformed to correct shape and position using a heat and a 2 Ton winch Inner surface of tank was polished to remove high points

  14. Assembly The amplifier was assembled in stages using many jigs that were made to align the fragile spring fingers into the coaxial structures of the amplifiers RF output 8 inch coax Triode socket in HT tank Motor drive anode tap

  15. HT input Water in and out at 35kV 6 inch coax RF power out Output capacitor

  16. We operate at constant HT with cathode modulation – cathode switched by IGBT between -400V to earth to switch tube into conduction Triode tube socket Moveable output capacitor TH116 triode

  17. Triode testing June 2012 With an old triode valve fitted (to be safe) at 32kV 72A = 2.3 MW electrical power per pulse we achieved 1.0MW RF power into a test dummy load No significant microwave of X-Ray hazard was observed from the amplifier system while it was on Triode tube in HT tank HT and water

  18. Power supply problems After a number of technical issues, power supply trips at 32kV power supply tube protection device (crowbar) was finally identified as the problem 140uF Capacitor bank (110kJ sorted energy) must be discharged in 5uS to prevent damage to tube in event of an arc New crowbar had to be fitted Crowbar protection device Amplifier system running into test load

  19. June 2013 – MICE RF parameters archived • First triode final stage amplifier had demonstrated 1ms pulses at 1Hz, 2.06MW @ 201.25MHz • Up to 34kV bias, operation with good gain achieved • Performance achieved: • 2.06MW output RF • 34kV bias voltage • 129A forward average current • h=46% (electronic) • Gain 10.8dB • Input port return loss -12.5dB • VSWR 1.6 • Drive from Tetrode • 170kW output RF • 18kV bias voltage • 15.5A forward average current • h=61% (electronic) • Gain 19dB • Drive from SSPA • 2.27kW

  20. The challenge has been achieved

  21. MICE experimental hall

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