Development of an ultra thin beam profiler for charged particle beams

摘要

Beam profiling during patient treatment in protontherapy requires ultra-thin monitors to preserve the high beam quality. For detectors upstream in the line, a material budget as low as similar to 15 mu m water-equivalent is needed. In addition, the current trend of dose escalation to treat highly resistant tumors implies challenging requirements on monitor radiation hardness and dynamic range. We propose a new type of beam profiler, PEPITES, using secondary electron emission (SEE) and built with thin-film techniques. The beam is profiled by crossing a pattern or a series of patterns which emit the SEE signal and can be made ultra-thin as SEE originates from the few nanometers next to the surface. The patterns are deposited on membranes, which, in contrast with common systems like ionization chambers, are free from mechanical constraints and can then afford higher absorbed doses and be as thin as achievable. A simple demonstrator prototype has been built and successfully operated with a proton beam at the ARRONAX cyclotron at St Herblain in a wide range of currents (100 fA to 10 nA) and several energies (30 - 68 MeV). Beam profiling results from these tests are presented, and our plans for the next prototypes are mentioned.