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Title A Mechanical Tuner and RF Drive Line System for the  ISAC II Quarter Wave Superconducting Cavities
Type Poster coupler / tuner / controls
Abstract The ISAC-II medium beta cavities have a design gradient of 6MV/m. This corresponds to a peak surface field of 30MV/m and a stored energy of U=3.2J and is a significant increase over other operating heavy ion facilities. To achieve stable phase and amplitude control the natural bandwidth of +-0.1Hz is broadened by overcoupling to accommodate detuning by microphonic noise and helium pressure fluctuation (1Hz/Torr). The chosen tuning bandwidth of +-20 Hz demands a cw forward power of 200 watts and peak power capability of 400 watts to be delivered to the coupling loop at the cavity. Two complimentary developments are ongoing at TRIUMF to achieve the design goal. In the first a new rf coupling loop is being developed with the goal to operate at 200W forward power with less than 1W of power being added to the helium load. The coupler has a thin stainless steel body for thermal isolation and a copper outer conductor cooled with LN2. Cooling of the inner conductor is achieved by adopting a thermally conducting Aluminum Nitride dielectric localized in the loop. Secondly TRIUMF is developing a mechanical tuner capable of both coarse (kHz) and fine (Hz) frequency adjustments of the cavity. A 1 mm thick Niobium plate at the high field end of the cavity is actuated by a vertically mounted permanent magnet linear servo motor, at the top of the cryostat, using a zero backlash lever and push rod configuration through a bellows feed-through. The demonstrated tuner resolution is better than 0.1 micro-m (0.6Hz) with a dynamic range of 8 KHz and a manual coarse tuning range of 33kHz. The response bandwidth is presently limited to 20Hz by a mechanical resonance  but is sufficient to accurately follow changes in cavity frequency due to variations in the helium pressure to a rate of several Hz/second. Mechanical details and cold test results of the ISAC-II coupling loop and mechanical tuner will be given.

List of authors...

Principle author first.

Last (Family) Name First Name (Initials only) Affiliation or Organization (abbreviations if possible)
Poirier R TRIUMF
Zviagantsev V TRIUMF

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