Faraday Cup for high current and duty cycle electron LINACs

Abstract

The design of a Faraday Cup (FC) is presented. The FC is designed to be used at an industrial LINAC test beamline. The present study gives the comprehensive design of FC to minimize the effects of secondary electrons. It also describes the heat dissipation at collector and its cooling design. A 200 mm long FC with aperture diameter of 20 mm and back wall thickness of 30 mm with repeller ring is simulated in CST particle studio software. A repeller ring is optimized for its thickness and axial distance to minimize the escape percentage of secondary charges from FC. The change in the thickness of repeller ring, axial distance and barrier potential greatly influence the escaped percentage. The study incorporates the secondary electron source at back wall of FC with fixed emission of 1.5 × 104 particles having energy 500 eV (10% dispersion) with different angular spread i.e. 0°, 45°, 90°. The escape percentage less than 1% is observed for 7 mm repeller ring-FC distance and 3 mm thickness with barrier potential of −700 V. The optimized design of the repeller ring reduces the physical dimensions of the FC. Moreover, the study also presents the mechanical design and heat transport analysis of Faraday cup. The designed square type channels with water circulating at 20 L/min limits the temperature to 333 K at the surface of the FC. Initial experimental results for thermal design are also presented, showing that temperature rise under 6 MeV, 4 μsec pulse width and 100 Hz repetition rate; is limited to 304 K. The cooling efficiently mitigates the heat load at water flow rate of 7.5 L/min.