Repeated Pulse Electron Beam Source for Materials Science Applications

Abstract

The divertor is one of the most energy-loaded elements of the ITER experimental tokamak. During the ITER operation, the divertor experiences both stationary thermal loads and rapid thermal impacts owing to transient processes in the plasma. The potentially most harmful transients during normal operation are edge-localized modes (ELMs). To mitigate the thermal impacts caused by ELMs, a current approach involves reducing the energy content of individual ELMs by increasing their frequency (up to 30–60 Hz). Because of the high pulse repetition rate, ~10⁸ ELM events are expected during the foreseen lifetime of the divertor components. Such a large number of pulses can lead to thermocyclic fatigue of the divertor material, the formation of a microcracks network, and melting along the edges of cracks as a result of failure of heat conduction. At the Budker Institute of Nuclear Physics, an experimental stand to study the performance of plasma-facing materials under the influence of a large (≥10⁷) number of ELM-like thermal impacts is being developed. To simulate the thermal impact on the material surface, it is planned to use a pulsed electron beam. In the present article, the prototype of an electron beam source for materials science research and the results of the beam characterization experiments are described. In experiments on electron beam generation, a beam current of 10 A at an accelerating voltage of 19 kV was achieved. The beam pulse duration of 1 ms at frequencies up to 10 Hz was demonstrated. Using imaging diagnostics based on luminescent ceramics, the beam current distribution was measured. The achieved beam parameters correspond to a specific power of 1.27 GW/m², which meets the requirements for materials science applications in the interests of fusion-class facilities.