Nonperturbing electron beam probe to diagnose charged-particle beams

Abstract

A nonperturbing diagnostic tool which is capable of precisely measuring the position and charge distribution of charged-particle beams, including those from rf accelerators, is described. The diagnostic uses as a probe a low-energy (1–20 keV), μA-level electron beam, which is injected across the path of the primary beam to be diagnosed. The probe electrons are deflected as they pass near or through the primary beam, after which they are collected by a suitable detector. The deflection of the probe electrons depends on the position of the primary beam relative to the test beam as well as on the charge distribution of the primary beam. Consequently, by measuring the deflections, one can determine these primary beam parameters. Calculations which illustrate the capabilities of this technique are presented, and the design and performance of a prototype version of the diagnostic are described. The prototype results agree very well with the calculations, verifying the theory and demonstrating the fundamental soundness of the approach for measuring the position and charge distribution of a relativistic beam. Although the prototype has only been tested with relatively low-energy beams (<500 keV), the extension to highly relativistic beams is straightforward and completely described by the theory. Based on these results, we have a very high degree of confidence that the diagnostic is fully capable of operating as predicted by the calculations.