Pressurized RF Cavities for Muon Ionization Cooling

70255B02-II Ionization cooling, a method for shrinking the size of a particle beam, is an essential technique for future particle accelerators that use muons. In particular, future muon colliders and neutrino factories will require high voltage radio frequency (RF) cavities for ionization cooling. Unlike any previous particle accelerator, muon beams in an ionization cooling channel must be accelerated through an energy absorbing material. This project will develop very high voltage RF cavities by filling them with cold, pressurized helium or hydrogen gas, which also will serve as an energy absorber to suppress high-voltage breakdown. Phase I built an RF test cell suitable for testing the breakdown characteristics of gases to be used in ionization cooling applications. The test cell passed Fermi National Accelerator Laboratory safety requirements and was used at the laboratory to measure the breakdown of hydrogen and helium gases under high-pressure and low-temperature conditions at 805 MHz. Phase II will develop RF cavities, pressurized with dense hydrogen or helium gas, that are suitable for use in muon cooling and accelerator applications. Measurements of RF parameters (e.g. breakdown voltage, dark current, quality factor) for different temperatures and pressures in magnetic and radiation fields will be taken in order to optimize the design of prototypes for ionization-cooling demonstration experiments. Commercial Applications and Other Benefits as described by awardee: The estimated cost of the ionization-cooling component of each muon collider or neutrino factory is roughly $350 million. By allowing the voltage of the RF cavities used in these applications to be significantly increased, this technology should lead to a correspondingly shorter cooling channel and lower cost.