Speaker
Description
See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1053.pdf
Measurement of edge ion temperature is critical to understand the underlying physics of the island configuration effect on the plasma transport. Here, the Ti profile at the plasma boundary has been successfully measured on W7-X during the last experimental campaign OP1.2b by a retarding field analyzer (RFA) probe. The RFA probe head was mounted on the front-end of a multipurpose manipulate (MPM) located at the middle plane of W7-X. The edge ion temperature profile has been studied by slightly varying the edge island size by changing the control coil current Icc, ECRH heating power PECRH and plasma density in the standard configuration (EIM+252). The experimental observations show that in the EIM+252 configuration, an ion temperature shoulder has been observed near the location where a sudden change of the field line connection length appears in the scrape-off-larger (SOL) region. The ion temperature measured at the edge shoulder region (Tish) decreased when the island width was expanded. For a fixed control coil current, Tish increases gradually with the increase of the ECRH heating power. A decrease of Tish was also observed when the central line-integrated electron density, nel , increases from 7×10^19 m^-2 to 9×10^19 m^-2. Nitrogen seeding injection from the upper horizontal divertor port M51 was performed on W7-X, a significant reduction and flattening in the edge ion temperature profile has been observed. In addition, the edge ion-to-electron temperature ratio tau_i/e has been calculated which gradually increases with the major
radius from the edge plasma to the far SOL region. An extended two-point model including upstream ion temperature is introduced to understand the experimental measurement. The edge plasma parameters are also reconstructed by a much more complete 3D simulation code, EMC3/EIRENE, and compared with the RFA measurement. This work may help to understand the plasma transport in the island configuration in the W7-X stellarator.
