Foil hits reduction by minimizing injection beam size at the foil in J-PARC RCS

Saha, P. K.   ; Yoshimoto, Masahiro  ; Okabe, Kota  ; Harada, Hiroyuki  ; Tamura, Fumihiko   ; Hotchi, Hideaki*

Uncontrolled beam loss caused by foil scattering of the circulating beam causes high residual radiation at the injection area of J-PARC 3-GeV RCS. It is thus one big issue towards beam intensity ramp up and operation at the designed 1 MW beam power. We studied to reduce foil hits by minimizing the vertical injection beam size at the foil and using a smaller vertical foil size. We obtained 30% reduction of the foil hits, consistent with numerical simulation and it has already been implemented for 700-KW operation at present. The present result thus plays an important role to realize and maintain a stable operation at 1-MW beam power in the RCS.