New local field quantity describing the high gradient limit of accelerating structures

Abstract

A new local field quantity is presented which gives the high gradient performance limit of accelerating structures due to vacuum rf breakdown. The new field quantity, a modified Poynting vector S c , is derived from a model of the breakdown trigger in which field emission currents from potential breakdown sites cause local pulsed heating. The field quantity S c takes into account both active and reactive power flow on the structure surface. This new quantity has been evaluated for many X-band and 30 GHz rf tests, both traveling wave and standing wave, and the value of S c achieved in the experiments agrees well with analytical estimates.

Advances in the Understanding of the Physical Processes of Vacuum Breakdown

“…Breakdown rate (BDR) is observed to depend very strongly on the field level in the structure [4], and can be approximated by BDRαE 30 [5]. Experimental data of BDR vs. E is shown in fig.…”

Multi-harmonic cavity for suppressing surface pulsed heating

“…1(c) shows quantitatively, due to the quadratic dependence of upon , that there is an optimal range of such that , which means it is possible to have lower temperature rise with two modes than for a single mode alone, while maintaining the same acceleration gradient. The modified Poynting vector [4], and total required RF power , also follow a quadratic dependence on the mode percentage , so use of two modes is expected to lower and as well. The reduction of the total required RF power indicates the RF-to-beam efficiency can also be improved with multi-harmonic operation.…”

Optimized operation of dielectric laser accelerators: Single bunch

“…Throughout the years several dielectric structures have been proposed [9][10][11][12] and more recently experimental results were reported [13][14][15]. In all these configurations fluence damage [16] is a limiting factor, whereas in rf machines, breakdown at the metalvacuum interface is a critical impediment [17].…”