First Results on a 500 MHz Superconducting Test Cavity for TRISTAN

Abstract
First results on measurements of a 500 MHz superconducting cavity for TRISTAN are reported. The cavity of spherical shape has been built from 2.5 mm niobium sheet of 99.6% purity by spinning, the main impurity being 1700 ppm of tantalum. Electropolishing and oxipolishing techniques have been applied for surface treatment. No high temperature degassing has been carried out. A Q-value of Q 0=3.4×109 and an accelerating gradient E acc=4.1 MV/m have been obtained at 4.2 K. At 1.9 K the Q-value has been improved to Q 0\gtrsim1.1×1010.

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