Design of a Demonstration of Magnetic Insulation and Study of its Application to Ionization Cooling for a Muon Collider

A key challenge for a muon collider is to cool (i.e., reduce the emittance of) the muons, which is achieved by strongly focusing them as they pass through absorbers, followed by their re-acceleration in RF cavities. This focusing process requires strong solenoidal magnetic fields that, in practice, penetrate into the RF cavities. Experiments have shown these solenoidal fields can damage vacuum cavities and reduce operating gradients, apparently from field-emitted `dark currents¿ that are accelerated by the RF and focused by the solenoids onto other surfaces. A promising solution to this problem is ¿Magnetic Insulation,¿ an established technique for suppressing breakdown in dc or pulsed voltage applications; however, its use with RF is a recently proposed concept. This project will design a magnetically insulated accelerating cavity with cavity walls shaped to closely follow the magnetic field lines on all surfaces with significant RF surface gradients. With this configuration, all field-emitted `dark currents¿ will be returned by these magnetic fields to their surface of origin with non-damaging energies less than 1 KeV. Commercial Applications and other Benefits as described by the awardee: The technology should help enable the construction of a muon collider, which would have an important advantage over an electron linear collider (such as the ILC): due to the high mass of the muons, it¿s beams could be accelerated and stored in rings, allowing for a smaller machine foot print and, hopefully, lower cost