A very High Gradient Test of a 30 GHz Single-Cell Cavity

In order to extend the available range of data on achievable accelerating gradients and pulse lengths at the CLIC (Compact Linear Collider) frequency of 30 GHz, a single-cell resonant cavity has been high-gradient tested in the CLIC Test Facility, CTFII. The cavity was excited by a 4 ns long bunched electron beam, resulting in a field pulse with a steep rise, followed by an exponential decay with a 1/e time of 25 ns (corresponding to a loaded Q of 3800). The cavity operated without breakdown at a peak accelerating gradient of 290 MV/m, with operation progressively less stable with increasing gradient. At about 400 MV/m the cavity broke down on every pulse. For this condition the cavity surface was subject to a surface electric field in excess of 750 MV/m.