Experimental simulation of Edge Localised Modes using focused electron beams - features of a circular load pattern

The knowledge about degradation processes caused by Edge Localised Modes (ELMs) on plasma facing materials (PFMs) in future confinement experiments is essential to allow lifetime estimations for first wall and divertor components. Electron beam simulations of the occurring heat loads have the advantage to be able to work at higher frequencies compared to other experiments (e.g. plasma streams), allowing a large number of ELM-like heat pulses. This paper deals with the electron beam guidance method used in the JUDITH 2 facility in Forschungszentrum Jülich (Germany). As the beam is described well by a Gaussian profile with a variable FWHM, depending on several parameters, e.g. vacuum pressure, the guidance is of special interest in order to achieve an approximately homogeneous (ELM-like) loading. A circular pattern turned out to provide advantages, in particular related to an increased stability against beam width fluctuations.