Design and Validation Strategy for an X-Ray Target Subject to Ultra High Heat Flux Loading

Abstract

Microbeam X-ray therapy is a promising cancer therapy that uses a high-power electron beam hitting a metallic target. For a clinical microbeam therapy X-ray source, an electron beam of a power of 1 MW onto a focal spot of 0.05 mm × 20 mm size is needed, with a penetration depth of 0.1 mm. This means a heat flux input of 1 TW/m2, an order of magnitude higher than nuclear and medical applications. Numerical simulations based on surface and volumetric heat loading for such an electron beam are presented in this work. The local temperature around the focal spot is modeled in a lower-scale model with an element size of 10 µm and volumetric heat loading. This differs from the state-of-the-art simulations, in which electron beam loading is modeled as surface heat flux loads. The simulated temperature agrees with the mathematical estimates within an error of 10% while proving feasibility. A novel validation strategy is proposed to address the lack of available test facilities to replicate this extreme heat flux. The critical parameters describing the high-heat-flux-loading are identified as temperature, thermal strain, thermal stress, and strain rate. Scaled-down test specifications are determined to use a test facility of power less than 100 kW. With the verified simulation using the scaled-down test, it is proposed to establish the material's capability to withstand the concentrated 1 MW heat load without a 1 MW test facility.