A general analysis of thin wire pickups for high frequency beam position monitors

Abstract

In many particle accelerators, a large number of high-frequency beam position monitors (BPMs) are required to track and correct the orbit of the beam. Therefore, simple, sensitive, low-cost pickup designs for such BPMs are of widespread interest. In this paper, a general analysis of arbitrarily terminated thin wire stripline or “wireline” pickups for BPMs is presented. Subsequently, three specific cases of interest, the open-circuited end, short-circuited end, and matched end wirelines are compared and contrasted in detail. Of these three cases, the open-ended wireline pickup BPM is found to be particularly well-suited for application in the arc regions of the Continuous Electron Beam Accelerator Facility (CEBAF). Measurements of a 1.5 GHz prototype of this type of BPM yielded a longitudinal (sum) pickup impedance of 72 ω, a transverse pickup impedance of 3.8 ω/mm, and a bandwidth of 470 MHz, all of which are in excellent agreement with the theory.