Acceleration of Positive Muons by a Radio-Frequency Cavity

Acceleration of positive muons from thermal energy to 100 keV has been demonstrated. Thermal muons were generated by resonant multiphoton ionization of muonium atoms emitted from a sheet of laser-ablated aerogel. The thermal muons were first electrostatically accelerated to 5.7 keV, followed by further acceleration to 100 keV using a radio-frequency quadrupole with an intensity of 2×10^{-3}  μ^{+}/pulse. The transverse normalized rms emittance of the accelerated muons in the horizontal and vertical planes were 0.85±0.25(stat)_{-0.13}^{+0.22}(syst)   π mm mrad and 0.32±0.03(stat)_{-0.02}^{+0.05}(syst)   π mm mrad, respectively. The measured emittance values demonstrated phase-space reduction by a factor of 2.0×10^{2} (horizontal) and 4.1×10^{2} (vertical) allowing good acceleration efficiency. These results pave the way to realize the first-ever muon accelerator for a variety of applications in particle physics, material science, and other fields.