Surface Loss Probabilities of Neutral Hydrocarbon Radicals on Amorphous Hydrogenated Carbon Film Surfaces: Consequences For The Formation of Re-Deposited Layers in Fusion Experiments

Abstract

The success of present-day fusion experiments relies on the use of a divertor which efficiently pumps impurities generated by erosion of the first wall. In most fusion experiments the divertor surface consists of graphite tiles or carbon fiber composites. They are bombarded by ions from the scrape-off layer which are guided into the divertor by the magnetic field. This impinging ion flux leads to sputtering of the divertor tiles releasing carbon and hydrocarbon compounds into the gas phase. This emitted carbon flux is excited in the divertor plasma and dissipates the plasma power via radiation, leading to a reduction of the heat flux onto the divertor surface. Most emitted carbon and hydrocarbon species re-deposit promptly in or in proximity to the divertor. This balance between deposition and erosion is crucial for the performance of a divertor in a next-step device, since the total lifetime before replacement strongly depends on the ability to control this re-deposition.