Multipactor at SDTL cavity in J-PARC linac

Ito, Takashi  ; Hirano, Koichiro  ; Nammo, Kesao*

After the recovery works from an earthquake, we started a high power conditioning of a DTL and an SDTL on November 2011 and restarted a beam acceleration on December 2011. The operation of the DTL and the SDTL was stable as with the operation before the earthquake without SDTL05B cavity. It was impossible to input an RF power into the SDTL05B in the about 300 kW to 400 kW range. Therefore the operating power was increased to 510 kW that is about 1.4 times those of before the earthquake. We have investigated the cause of this malfunction of SDTL05B, and a computer simulation showed that it is likely to be caused by a multipactor on the surface of the cavity wall. In this paper we present the result of the simulation, the various measurements and the countermeasure.