Beam characterization of medium energy transport line (MEBT1) to improve beam emittance in J-PARC linac

Yanai, Kyosuke; Iinuma, Hiromi*; Otani, Masashi*; Kondo, Yasuhiro   ; Hirano, Koichiro  ; Miyao, Tomoaki*; Moriya, Katsuhiro  

Currently, in the J-PARC linac, the emittance growth of 20 to 30% between the radio frequency linac (RFQ) and drift tube linac (DTL) in an large issue. The mismatch into the DTL is a candidate of the reason and precise beam measurement at the medium energy beam transport (MEBT) is necessary. The emittance and twiss parameters are now measured using Q-scan method, but the systematic error of this measurement is not yet fully evaluated. To this end, the measured emittance with Q-scan method and that with double-slit type emittance scanner should be compared to evaluate the measurement accuracy. We conducted this measurement at an RFQ test stand. Currently, there are difference of 2-3 mm between the measured profile and the simulation. The RFQ simulation needs to be reconsidered. The beam based alignment of the beam profile monitor has been performed also. The difference of 1mm between the magnetic and BPM center is observed, and the reason is under investigation. In this paper, these beam measurements are described.