First Results on a 500 MHz Superconducting Test Cavity for TRISTAN

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 Qo = 3.4 × 109 and an accelerating gradient of Eacc = 4.1 MV/m have been obtained at 4.2 K. At 1.9 K the Q-value has been improved to 1.1 x 1010. Gas condensation and degassing effects on the cavity are also reported.