Evaluation of plasma impurity concentration during radiative divertor operation mode on EAST

Abstract

BackgroundBy injecting gaseous neon (Ne) or argon (Ar) into the divertor region, the radiative divertor operation mode has been successfully realized on experimental advanced superconducting tokamak (EAST). During the radiative divertor operation phase, the damage to divertor plates is effectively mitigated by reducing heat load from high energy particles. However, the injected excess impurity gas may penetrate the last closed flux surface and transport to the core region, causing the degradation of core plasma confinement.PurposeThis study aims to develop an evaluation method to measure the core impurity concentration for assessment the effects of injected impurity on the confinement of core plasma.MethodsThe absolute intensity of impurity radiation characteristic line was measured and calculated in combination with collisional radiation model (CR model), and different evaluation methods of impurity concentration were developed for different impurity species. The concentration of impurity tungsten (W) was evaluated by combining the radiation intensity measurement from extreme ultraviolet spectroscopy and CR model whilst the concentration of impurity Ne was assessed on the basis of measurement of effective charge number (Zeff). The impurity level in the core region was analyzed in details.ResultsMeasurement and model calculation results show that the concentration of Ne and W impurities in the core increases significantly after Ne impurity injected.ConclusionsThe evaluation method in the study is important for evaluating confinement in the core region during radiative divertor and improving plasma performance.

Keywords

• impurity concentration
• impurity transport
• radiative divertor operation
• extreme ultraviolet spectroscopy
• effective charge number