Reduction of transverse emittance growth in J-PARC linac DTL

Sako, Hiroyuki   ; Wei, G.; Miura, Akihiko ; Ikegami, Masanori*

In J-PARC linac at 15 mA, horizontal and vertical emittance after DTL is reduced by 12% and 10%, respectively by setting the amplitudes of the first and second bunchers to 120% and 90% with respect to the designed settings. The resulting normalized horizontal and vertical emittance is 0.230 and 0.205 mm mrad. At 20 mA measured in Jan 2010, horizontal and vertical rms emittance is reduced by 17% and 10% respectively by setting the amplitudes of the first and second bunchers to 110% and 80% with respect to the designed settings. The resulting normalized horizontal and vertical emittance is 0.273 and 0.253 mm mrad. At 15 mA, we further investigated dependence of emittance on quadrupole magnetic field in MEBT1. With the most downstream quadruple magnet field at MEBT1 enhanced by 20% from the designed values, the emittance is further reduced to 0.171 and 0.200 mm mrad. These results are compared with the IMPACT simulation.