Gaseous hydrogen for muon beam cooling

Muons, despite their short lifetime, have an advantage in that they can be accelerated through matter without suffering appreciable scattering as do strongly interacting protons or electromagnetic showering as do less massive electrons. Thus RF cavities filled with dense gas to suppress electrical breakdown can provide high gradients for relatively short muon ionization-cooling channels for Neutrino Factories and Muon Colliders. Hydrogen gas, with large dE/dx, radiation length, and heat capacity, also acts as the perfect energy absorber having several engineering advantages. The progress of a DOE STTR grant project to develop high-pressure high-gradient RF cavities is described. First measurements of RF breakdown curves are reported, where stable operation was achieved with surface gradients of 50 MV/m for hydrogen and 28 MV/m for helium.