Measurement of plasma flows into tile gaps

Particle fluxes falling into narrow gaps are of high interest since international thermonuclear experimental reactor plasma facing components will be castellated. In order to investigate the plasma deposition in gaps between tiles, we have developed a special probe that recreates a gap and that can measure the ion saturation current profiles along its both sides. Measurements were performed in the tokamak Czech Academy of Sciences TORus and are compared with a self-consistent kinetic model. The simulations reproduce well the observed asymmetry of the plasma deposition in both poloidal and toroidal gaps and the intensity of the collected currents is well-estimated. However, the agreement is less perfect for poloidal gaps due to the presence of a positive peak on the negative potential inside the gap. Therefore, the plasma deposition does not decay exponentially like in toroidal gaps. Nevertheless, this unique set of experiments confirms globally the results of our model.