Design of the ridge filter type modulator for TR103 of PEFP

The PEFP (Proton Engineering Frontier Project) plans to start the beam service from 2013. We will provide proton beam to the users at the user facilities, TR103 and TR23. The user facility consists of energy degrader, flux controller, scatterer, ridge filter type modulator, target stage, diagnostic system, collimator and so on. In this study, we designed a ridge filter type modulator for the uniform depth dose distribution with high LET (linear energy transfer) value. Currently, there are two types of range modulator for SOBP (spread out Bragg peak). One is a propeller type, and the other is a ridge filter type modulator. A propeller type modulator is not suitable for a pulsed beam because it has time dependent property. So, it is difficult to apply a short pulsed beam of the PEFP because the range of pulse length is 0.1 ∼ 1.33 msec. for 103 MeV. Unlike a propeller type one, ridge filter type modulator has no restriction. For these reasons, we choose the ridge filter type modulator for the energy modulation. The aluminum was selected a s a material of modulator, because it can be cooled down in the very shorter time after proton beam irradiation compared to graphite, another candidate. So we selected aluminum as a material of a ridge filter type modulator