Development of negative muonium ion source for muon acceleration

Abstract

A negative muonium ion (Mu-) source using an aluminum foil target (Al target) was developed as a low-energy muon source. Mu- ions are produced by irradiating the Al target with a 3-MeV positive muon (μ+) beam and observed using a microchannel plate. An experiment to produce Mu- ions was conducted to evaluate the performance of this Mu- ion source. The measured event rate of Mu- ions was (1.7±0.3)×10-3 Mu-/s when the event rate of the incident μ+ beam was 1.3×106/s. The experiment was conducted at the Muon Science Establishment, D-line in the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex. The formation probability, defined as the ratio of the Mu- ions to the incident muons on the Al target, was (1.1±0.2(stat)+0.1-0.0(syst))×10-6. This Mu- ion source was first adopted in the commissioning of the muon accelerator at the D-line, and the event rate of the accelerated Mu- ions was consistent with the expectation. This Mu- ion source boosted the development of the muon accelerator, and the practicality of this low-energy muon source obtained using a relatively simple apparatus was demonstrated.