Spoke cavity power coupler conceptual design work for the HEL-JTO beam exp.
The objective of this report was to create a low-cost, modest-power RF coupler for a SRF spoke cavity beam test of electrons test to be done at LANL. Developing the design for this magnetically-coupled SRF spoke cavity testing coupler was basically straightforward since the cavity coupling port needed to be one of the 1.22-inch ID ports, and the power level was limited by the available RF to less than 400 W TW power. In addition, the coupler would be immersed in bath cryostat filled with liquid helium, and ultimately used in a pulsed mode to accelerate beam, thereby significantly relaxing the thermal loads on the coupler. Combining the above considerations with the level of resources available for this task, emphasis was placed on rapidly developing a robust, reliable design that would use commercially-available components as available to save design, engineering, and fabrication costs. Analysis was also kept to a minimum. As such, the design incorporates the following features: (1) Use of a commercially-available Type-N ceramic feedthrough. For the power and frequency range of the test, with the feedthrough immersed in LHe, it was felt the Type-N feedthrough would provide a robust, low-cost vacuum window solution. (2) The coupler outer conductors would be solid OFE copper that is brazed into two 2.75-inch CFF, with the cavity-sde flange being rotatable to allow minor Qx adjustments by rotating the coupler. The braze joint shown has the copper brazed into a groove in the SST to ensure maximum strength for successive thermal cyclings. The outer wall of the copper between the two flanges serves as the heat sink for depositing coupler heat to the liquid helium. (3) The inner conductor would be solid OFE copper brazed to the outer conductor at the top to ensure maximum thermal conductivity from the outer thermal sink area to the base of the feedthrough. A mass-reducing hole is placed down the center of the inner conductor to decrease thermal mass and weight. (4) This assembly would be mated to the Type-N feedthrough by pushing the pin from the feedthrough into a spring-loaded connector on the base of the inner conductor, then bolting the flanges together. (5) If the coupling needs to be greatly reduced, an additional 1/2-inch CFF can be inserted between the coupler and cavity flanges. Increasing the coupling can be done with a 3 stub tuner.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 923120
- Report Number(s):
- UCRL-TR-235434; TRN: US0802208
- Country of Publication:
- United States
- Language:
- English
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