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XX International Linac Conference

THD04 (Poster)

Presenter: Steve Virostek (LBNL)
Status: Complete
FullText: pdf
Eprint: physics/0008169

Analysis of Thermally Induced Frequency Shift for the Spallation Neutron Source RFQ*

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[1] 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[1] 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.
[1] Trademark
* 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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