High gradient experiments by the ATF

A high gradient experiment using traveling wave structures at S-band frequencies is presented. The experiments have been carried out using the ATF (Accelerator Test Facility) phase-I linac. A 0.6-m-long constant-gradient traveling-type structure was utilized to generate the maximum accelerating gradient of 100 MeV/m at 200 MW of RF peak power. The dark current dependence on the structure length and the effect of a dustless and dielectricless structure are discussed. It is concluded that the clean structure of low-dust and low-dielectric material would be suitable for decreasing the dark current one order lower than the normal structure by a standard fabrication process.<>