Magnetically insulated high-gradient accelerating structures for muon accelerators

Reduction of the available accelerating gradient in cavities exposed to external magnetic fields is a longstanding problem which limits the performance of many systems, especially muon accelerators. We propose a novel idea for improving the cavity's gradient by suppressing breakdown events caused by field emissions on its surfaces. The concept involves designing an rf cavity wherein its walls are parallel to the contour lines of the external magnetic fields, thereby preventing field-emitted electrons from leaving the surface, and subsequently picking up energy from the rf electric field. We present a conceptual design of a muon accelerator cooling lattice with magnetically insulated cavities and detail its expected performance. Our results suggest that the magnetically insulated cooling channel we describe, although demanding in rf power, can produce enough initial beam cooling to be a feasible option for a muon collider or a neutrino factory.