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Unwanted field emission is a well known problem for high-gradient accelerating structures as it can cause damage and initiate breakdown. Recent experiments indicated that the deleterious effects of field-emission are greatly enhanced in the presence of external magnetic fields. In the context of designing a muon accelerator this imposes numerous constraints since rf cavities need to operate within strong magnetic fields in order to successfully transport the beam. Here, a novel design of a magnetically insulated cavity in which the walls are parallel to the magnetic field lines is presented. We show that with magnetic insulation, damage from field emission can be significantly suppressed. Effects of coil positioning errors on the cavity performance are discussed and the required magnetic field strength to achieve insulation is estimated. We present a conceptual design of a muon collider cooling lattice with magnetic insulated cavities and cross-check its performance to the one with pillbox cavities. Finally an experiment to test magnetic insulation is described. [ABSTRACT FROM AUTHOR]

We discuss a possible implementation of high-pressure gas-filled RF (HPRF) cavities in a linear cooling channel for muons and some of the technical issues that must be dealt with. The approach we describe is a hybrid approach that uses high-pressure hydrogen gas to avoid cavity breakdown, along with discrete LiH absorbers to provide the majority of the energy loss. Initial simulations show that the channel performs as well as the original vacuum RF channel while potentially avoiding the degradation in RF gradient associated with the strong magnetic field in the cooling channel. [ABSTRACT FROM AUTHOR]

It has been observed [1] that breakdown in an 805 MHz pill-box cavity occurs at much lower gradients as an external axial magnetic field is increased. This effect was not observed with on open iris cavity. It is proposed that this effect depends on the relative angles of the magnetic and maximum electric fields: parallel in the pill-box case; at an angle in the open iris case. If so, using an open iris structure with solenoid coils in the irises should perform even better. A lattice, using this principle, is presented, for use in 6D cooling for a Muon Collider. Experimental layouts to test this principle are proposed. [ABSTRACT FROM AUTHOR]