Development of the New Method to Measure Laser-accelerated Sub-GeV Protons Utilizing Multiple Coulomb Scattering in an Emulsion Cloud Chamber

Laser plasma proton acceleration, where it was recently reported that near-100-MeV proton acceleration was demonstrated, offers the potential to realize a compact and cost-effective accelerator in the future. Because it can generate an extreme electric field that is over six orders of magnitude higher than that of a conventional radio-frequency accelerator apparatus. To understand the underlying physics of the acceleration process and increase maximum proton energy, precise measurement of both the energy spectrum and the two-dimensional distribution is required. Against this background, we have developed a new measurement method for laser-accelerated sub-GeV-class protons using the nuclear emulsion. Based on the Multiple Coulomb Scattering (MCS) method in an Emulsion Cloud Chamber (ECC), which is a stack of nuclear emulsion films and scatterer plates, the incident energies were inversely evaluated by the scattering angle. The proof-of-principle experiment has been conducted with the Heavy-Ion Medical Accelerator in Chiba (HIMAC) to verify that the ECC is able to identify sub-GeV protons with the MCS method. Combined with a technique of machine learning, a new measurement method has been developed to obtain an energy spectrum of laser-accelerated sub-GeV protons by the ECC with the MCS method.
ICMaSS2021