Advanced accelerator theory development

Abstract

A new accelerator technology, the dielectric wall accelerator (DWA), is potentially an ultra compact accelerator/pulsed power driver. This new accelerator relies on three new components: the ultra-high gradient insulator, the asymmetric BlurnleiU and low jitter switches. In this report, we focused our attention on the first two components of the DWA system the insulators and the asymmetric Bhunlein. First, we sought to develop the necessary design tools to model and scale the behavior of the high gra&ent insulator. To perform this taslq we concentrated on modeling the discharge processes (i.e., initiation and creation of the surface discharge). In additio~because these high gradient structures exhibit favorable microwave properties in certain accelerator configurations, we pefiormed experiments and calculations to determine the relevant electromagnetic properties. Second, we performed circuit modeling to understand energy coupling to dynamic loads by the asymmetric Blumlein. Further, we have experimentally observed a non-linear coupling effect in certain asymmetric Blumlein configurations. That is, as these structures are stacked into a complete module, the output voltage does not sum linearly and a lower than expected output voltage results. Although we solved this effect experimentally, we performed calculations to understand this effect more filly to allow better optimization of this DWA pulse-forming line system. A new accelerator technology, the dielectric wall accelerator (DWA), is potentially an ultra compact accelerator/pulsed power driver [1]. Because of its compact size (which translates into lower cost), it has potential applications in several defase missions and in the commercial sector. It utilizes three principal components to achieve a high gradient in a compact structure. These components include the insulator, the asymmetric Blumlei% and the switches.A primary component that limits the acceleration gradient in the DWA is the vacuum insulator. We have expanded on the initial work [2], and fi.nther studied and developed this component over the past several years [3,4]. For short pulse systems, these structures have withstood 20 MV/m gradients in the presence of a plasma cathode and a 1 kA electron beam.The asymmetric Bhnnlein is a novel method for generating a f~electrical pulse in a single step process (F&ure 1). The system consists of a stacked series of these circular modules and generates a high voltage when switched. Each Blurnlein is composed of two dielectric layers with differing permittivities. On each surface and between the dielectric layers are conductors that form two parallel plate radial transmission lines. The lower permittivity side of the structure is referred to as the slow line. The higher permittivity side of the structure is referred to as the fiist line.Operation of the Blumlein is as follows. The center electrode between the f~and slow line is initially charged to a high potential. Because the two lines have opposite polarities, there is no net voltage across the i...