Characteristics of the SOL ion-to-electron temperature ratio on the J-TEXT tokamak with different plasma configurations

Accurate measurement of the average plasma parameters in the edge region, including the temperature and density of electrons and ions, is critical for understanding the characteristics of the scrape-off layer (SOL) and divertor plasma transport in magnetically confined fusion research. On the J-TEXT tokamak, a multi-channel retarding field analyzer (RFA) probe has been developed to study average plasma parameters in the edge region under various poloidal divertor and island divertor configurations. The edge radial profile of the ion-to-electron temperature ratio, τ_i/e, has been determined, which gradually decreases as the SOL ion self-collisionality, \nu _\mathrmS\mathrmO\mathrmL^\mathrm* , increases. This is broadly consistent with what has been observed previously from various tokamak experiments. However, the comparison of experimental results under different configurations shows that in the poloidal divertor configuration, even under the same \nu _\mathrmS\mathrmO\mathrmL^\mathrm* , τ_i/e in the SOL region becomes smaller as the distance from the X-point to the target plate increases. In the island divertor configuration, τ_i/e near the O-point is higher than that near the X-point at the same \nu _\mathrmS\mathrmO\mathrmL^\mathrm* , and both are higher than those in the limiter configuration. These results suggest that the magnetic configuration plays a critical role in the energy distributions between electrons and ions at the plasma boundary.