A Novel Multipactor Free and Deflecting Force Reduced Dielectric Accelerator X-ray Source for Ir-192 Replacement

Ir-192 is a major radiation source for many applications, e.g. high-dose brachytherapy. However, Ir-192 has a half-life of only 73.83 days, which limits its appeal, given the frequent need for replacement of the sources. This replacement is not only labor-intensive and expensive, but also presents a potential risk for criminal diversion. However, to date, there is no linac-based x-ray machine that can be carried around in a single piece and fit into tight spaces, and that is economically competitive as a replacement for radioactive isotopes like Ir-192. Dielectric accelerator is a good candidate for ultracompact low energy accelerators. But there is an inevitable technically challenging issue is, the occurrence of multipactor, which significantly reduces the RF efficiency. Leveraging the novel accelerator technology that is currently under development at Euclid Beamlabs, we propose to develop a small-sized accelerator-based radiation source that is compact and light enough to operate as a module for an easy stack-up to increase the deliverable radiation dose. The proposed novel accelerator consists mainly of a split dielectric tube whose design is intended to resolve the most challenging issue of multipactor, which has been preventing dielectric accelerators from being used in real applications. An additional benefit of having a split dielectric accelerator is the suppression of deflecting modes, because the surface currents needed to support such modes requires azimuthal components that the slits interfere with. Meanwhile, the accelerating mode only requires longitudinal surface currents. Suppressing the excitation of deflecting modes means higher currents can be transmitted through the structure. We will fabricate a prototype in Phase I and carry out the high power rf conditioning to verify its performance for multipactor suppression. The results from the project will also provide manifold public benefits. Such a system can be used for industrial radiography, replacing radioactive isotopes like Ir-192 and Co-60 for real-time examination and monitoring of civil infrastructure. Such systems can be made portable, since dielectric-loaded accelerating structures are transversely compact (borderline handheld), as opposed to truck-mounted irradiation systems. Because of the unprecedented compactness, other applications can be targeted, such as medical linac radiology gantries. These immense (few thousand lbs.), heavy patient irradiation systems have most of their weight in the shielding around the accelerating structure.