Investigation of the Ion Energy Transport in the Scrape-Off Layer on the J-TEXT Tokamak Using a Retarding Field Analyzer

Radial profiles of the ion temperature,Ti,have been measured by a double-sided retarding field analyzer（RFA） in the scrape-off layer（SOL） of the J-TEXT tokamak（R = 105 cm,r = 25-29 cm,Bt = 1.8-2.0 T,Ip = 120-180 kA,ne =（2-2.5） × 10^19 m^-3）.Strongly declining Ti profiles in the SOL have been found.The different e-folding lengths,At,of the Ti profiles in two experimental configurations with different magnetic connection lengths,Lc,reveal that a longer Lc results in weaker parallel energy transport and longer At.In similarity with the particle transport across the SOL,At is approximately proportional to the square root of Lc.Additionally,the poloidal asymmetry has been identified with enhanced ion energy transport across the SOL on the low-field side.

Multi-channel retarding field analyzer for EAST

A multi-channel retarding field analyzer（MC-RFA） including two RFA modules and two Langmuir probes to measure the ion and electron temperature profiles within the scrape-off layer was developed for investigations of the interplay between magnetic topology and plasma transport at the plasma boundary.The MC-RFA probe for the stellarator W7-X and first measurements at the tokamak EAST was designed.The probe head allows simultaneous multichannel ion temperature as well as for electron temperature measurements.The usability for radial correlation measurements of the measured ion currents is also given.

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,v_(SOL)*,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 v_(SOL)*,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 v_(SOL)*,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.