MICE Refurbishment of CERN RF equipment for MICE M. Vretenar, CERN AB/RF

MICE The CERN Linac1 Amplifiers Developed in (photo of 1959) for the old Linac1. Frequency MHz, equipped with the TH170R triode, can deliver a maximum of 2.5 MW with an anode voltage of 40 kV. 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.

MICE Linac1 amplifiers history  From the very beginning, these amplifiers experienced problems in reaching the peak power of 2.5 MW: breakdowns in the power extraction system (later modified to a single loop and used up to ~1.5 MW) and in the anode resonator. Linac1 (protons, heavy ions) was decommissioned in After Linac1 decommissioning a standard “modernization kit” (series of mechanical modifications intended to improve reliability and easy operation) has been developed for these units. Most of the Linac1 amplifiers have been modernized and reused in other installations: spare for Linac3 (400 kW), 1 for Linac2 RFQ (1 MW), 2 at the AD-RFQ (0.3 and 1.6 MW).

MICE What is left of the Linac1 amplifiers? 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.

MICE Maximum Power for Linac1 amplifiers F The maximum power achieved recently (1996) on these units was 1.7 MW (AD-RFQ final amplifier, power limited by sparking and matching of the output loop). The first demand from MICE was for 4 MW out of a single unit equipped with TH116. Discarded because required an expensive radical reconstruction of the amplifier (anode blocker capacitor, HOM suppression, double output, increased resonator diameter) and no guarantee of success (bad experiences in the past at CERN with pushing TH116 to its limits). Instead, preferred to prepare the 2 remaining amplifiers for 2 MW each. Only minor modifications (together with standard upgrade kits) should be required to go from the 1.7 MW measured in 1996 to 2 MW.

MICE Caveats F 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… F 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.

MICE Refurbishing details 2 “standard” upgrade kits will be applied to the amplifiers: 1.Add neutralization circuit, improve RF contacts and socket. 2.Modernize electronics: add industrial filament regulator controlled by PLC, new circuitry for transformer feeding. + replace the output loop with a “tapping”, which should allow increasing power from 1.7 to 2 MW. Work not going to be easy… many pieces have to be remade, and few drawings exist! We have to copy from our spare unit.

MICE What exactly we will do It is not possible to test the amplifiers with RF power at CERN (no anode supply, no RF drive). They will be tested at CERN up to the “filament” level: filament heating, test of cooling circuits. The RF part (input matching, resonator tuning, output matching) will be done to the “theoretical” calculated values. Input-outputs: - 3 1/8” input connector - 6 1/8” output connector (a bit at the limit for 2 MW…) - RG220/U cable for HV connection - electrical and water connections Note that for a DC power supply, these unit need a cathode switch circuit (not provided by CERN)

MICE 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: 1.Collect drawings, and design modified parts. 2.Make inventory of existing and missing parts. 3.Machine mechanical parts. 4.Dismount, clean, reconstruct amplifiers. 5.Assemble ventilation circuitry. 6.Assemble filament circuit and filament regulation (PLC based, CERN standard) 7.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: 1.Install cathode switch circuit (eventually also HOM suppressors). 2.Connect HV and RF loads. 3.Test with RF power.

MICE Status The 2 units for MICE (blue) and the spare CERN unit used as example (green)

MICE Other available RF equipment We have 2 old Linac1 Modulators (=pulsed anode supplies) for kV, ~80 A, 1 Hz, 200  s that we need to clear in order to free space. If they can be useful, please show up, otherwise at the beginning of March we will scrap them.