Studies of Laser Power Reduction for the Laser Stripping of 400 MeV H⁻ Beam at J-PARC RCS

Abstract

The H − (negative hydrogen) stripping to proton by using a solid stripper foil for charge-exchange injection is only an established way to achieve high-intensity proton beam in circular accelerators. However, a short and unexpected lifetime of the stripper foil, as well as uncontrolled beam losses and the corresponding residual radiation at the injection area, are two serious issues even with a moderate beam power. To avoid the realistic issues associated with foil, we proposed an alternative method of H − stripping by using only lasers. To establish our method, we are preparing for a Proof-of-Principle demonstration of 400 MeV H − stripping to proton by using lasers at Japan Proton Accelerator Research Complex (J-PARC). However, to achieve a higher stripping efficiency, the laser power is the most concerning issues in this case. To overcome this difficulty, we have studied both an extensive manipulation of the H − beam and advanced uses of the laser. These include utilizing a dispersion derivative of the H − beam to cope with its large momentum spread, while multi-pass laser system for multiple interactions of the H − beam with lasers. We have found that the laser power can be reduced to more than an order of magnitude by applying a combination of the two methods.

High-power proton accelerators for pulsed spallation neutron sources

“…For such a low energy, extremely high magnetic fields (>2T) are required for Lorentz stripping [54]. In order to avoid the difficulty, J-PARC has proposed an alternative nondestructive H − stripping method using only lasers [55,56], as shown in Fig. 25.…”