S. Virostek, J. Staples (LBNL)
The SNS Front-End Group at Lawrence Berkeley National Lab is developing an RFQ to accelerate an H- beam from 65 keV to 2.5 MeV at the operating frequency of 402.5 MHz. The 4 section, 3.7 meter long RFQ is a 4 vane structure operating at 6% duty factor. The cavity walls are made from OFE Copper with a GlidCop outer layer to add mechanical strength. A set of 12 cooling channels in the RFQ cavity walls are fed and controlled separately from the 4 channels embedded in the vanes. An ANSYS finite element model has been developed to calculate the deformed shape of the cavity for given RF heat loads and cooling water temperatures. By combining the FEA results with a SUPERFISH RF cavity simulation, the relative shift in frequency for a given change in coolant temperature or heat load can be predicted. The calculated cavity frequency sensitivity is -33 kHz per 1-deg C change in vane water temperature with constant temperature wall water. The system start-up transient was also studied using the previously mentioned FEA model. By controlling the RF power ramp rate and the independent wall and vane cooling circuit temperatures, the system turn-on time can be minimized while limiting the frequency shift.
* This work is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.
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