Multipactor suppression via higher-order modes

Abstract

Summary form only given. Multipactor is a resonant phenomenon in which an electromagnetic field causes a free electron to impact a surface, resulting in the surface emitting one or more secondary electrons. If the surface geometry and electromagnetic fields are appropriately arranged, the secondary electrons can then be accelerated and again impact a surface in the bounding geometry. If the net number of secondary electrons participating in multipactor is non-decreasing, then the process can repeat indefinitely. This phenomenon is of considerable practical interest in the design and operation of high power resonant structures. When the secondary electron yield (SEY) of a material measured as a function of the incident electron kinetic energy, the curve follows a similar shape for many materials: At low incident kinetic energies, the SEY is low; at intermediate kinetic energies, the SEY is maximized at a material-dependent energy; at high kinetic energies, the SEY tapers down to zero with increasing energy. In order multipactor to be self-sustaining, the average SEY over multipactor path must be at least unity. This means that multipactor can only be sustained within a certain material-dependent range of incident electron kinetic energies. This research investigates the feasibility of suppressing multipactor through the use of higher-order cavity modes which will modify the incident kinetic energy of impacting electrons. Since the SEY is dependent upon kinetic energy of the incident electron, our goal is modify impacting electron velocities to reduce the average SEY less than unity such that multipactor is not sustainable. Preliminary computer simulations are presented which demonstrate this concept in reducing or eliminating multipactor in a 2-dimensional coaxial cavity geometry.