Multi-Mode Cavity Design for Raising RF Breakdown Threshold in a Two-Beam High-Gradient Accelerator

Accelerator structures that can sustain acceleration gradients in the range of 150 MeV/m are required in order to build a future multi-TeV collider with an energy reach beyond present or planned electron-positron colliders. In order to overcome the limitations that would be expected to arise from RF breakdown and multipactor discharges, a cavity for a two-beam accelerator has been devised with an exceptional property: the cavity can be excited simultaneously in several harmonically-related modes, enabling the required strong fields to exist only during times when accelerated bunches are present in the cavity. This feature would be expected to mitigate against RF breakdown and pulsed wall heating, allowing the acceleration gradients to be greater than would be possible with single-mode cavity operation. In Phase I, cavities will design for experiments during Phase II, the goal of which will be to demonstrate an increase in the breakdown threshold. Commercial Applications and other Benefits as described by the awardee Structures that can sustain high accelerating gradients without an undue frequency of breakdown would be the basis for a future multi-TeV electron-positron collider and would hasten the day when commercial companies can obtain multi-million dollar manufacturing contracts for the accelerator structures.