Flexible chopper gate pulse generation for the J-PARC RCS

Tamura, Fumihiko   ; Yamamoto, Masanobu   ; Yoshii, Masahito*; Sugiyama, Yasuyuki*; Hotchi, Hideaki  ; Saha, P. K.   ; Yoshimoto, Masahiro  ; Harada, Hiroyuki  

Chopped beam injection is employed in the J-PARC RCS to avoid the longitudinal beam losses. A fast beam chopper is installed in the MEBT section of the linac. The chopper is driven by the gate pulses sent from the LLRF control system of the RCS. The delay from the zero crossing of the RCS rf and the width are set so that the beam pulse is injected into the proper phase position of the rf bucket. A unique feature of the J-PARC chopper gate pulse generation is thinning of the pulses. The thinning is useful to control the beam intensity without changing much the condition of the longitudinal painting. Also, the beam macro pulse can be trimmed down to a single intermediate pulse by setting the parameters. In this poster, we present the overview of the generation of the chopper gate pulse in the LLRF control system and various beam commissioning results utilizing the flexibility of it. Also, we discuss the upgrade of the chopper gate pulse generation.