Recent progress in KEK preinjector

The overall accelerating gap length is shortened to 18 cm in the high gradient accelerating column. A sparking rate of less than one per day is achieved by keeping a pressure of 2.5 x 10-4 torr in the column. The column current increases with the column pressure. It is plausible that the increased current is mainly due to molecular ions produced in a plasma expansion cup. The beam, which passes through focusing magnets, is scarcely affected by increasing the column pressure. An ion emissive plasma surface is located by a Langmuir probe. A multiple-canal duoplasmatron with seven anode holes is being developed