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Abstract: Limitations on the maximum achievable accelerating gradient of microwave cavities can strongly influence the performance, length, and cost of particle accelerators. Gradient limitations are widely believed to be initiated by electron emission from the cavity surfaces. Here, we show that the deleterious effects of field emission are effectively suppressed by applying a tangential magnetic field to the cavity walls. With the aid of numerical simulations we compute the field strength required to insulate an 805MHz cavity and estimate the cavity''s tolerances to typical experimental errors such as magnet misalignments and positioning errors. Then, we review an experimental program, currently under progress, to further study the concept. Finally, we report on two specific examples that illustrate the feasibility of magnetic insulation into prospective particle accelerator applications. [Copyright &y& Elsevier]

Abstract: Field emission in an rf cavity in the presence of external magnetic fields is examined. We show that emitted electrons from a sharp protrusion are focused by the magnetic field into small spots at another location in the cavity where they heat its surface. Scaling laws are established for the beam’s induced heat in terms of macroscopic quantities such as magnetic field, accelerating gradient and spot dimensions. We find that when the magnetic field is of the order of a Tesla, the induced thermal stresses by the pulsed electron flux exceed the elastic limit and the surface becomes prone to cycling fatigue. The implication of these findings on the observed surface damage and magnetic-field-depended breakdown of an 805MHz cavity is addressed. [ABSTRACT FROM AUTHOR]