EAST alternative magnetic configurations: modelling and first experiments

Abstract

Heat and particle loads on the plasma facing components are among the most challenging issues to be solved for a reactor design. Alternative magnetic configurations may enable tokamak operation with a lower peak heat load than a standard single null (SN) divertor. This papers reports on the creation and control of one of such alternatives: a two-null nearby divertor configuration. An important element of this study is that this two-null divertor was produced on a large superconducting tokamak as an experimental advanced superconducting tokamak. A preliminary experiment with the second null forming a configuration with significant distance between the two nulls and a contracting geometry near the target plates was performed in 2014. These configurations have been designed using the FIXFREE code and optimized with CREATE-NL tools and are discussed in the paper. Predictive edge simulations using the TECXY code are also presented by comparing the advanced divertor and SN configuration. Finally, the experimental results of ohmic and low confinement (L-mode) two-null divertor and SN discharges and interpretative two-dimensional edge simulations are discussed. Future experiments will be devoted to varying the distance between the two nulls in high confinement (H-mode) discharges.

Integrated plasma control for long pulse advanced plasma discharges on EAST

“…It has been verified the heat reduction capability by using so called snowflake (SF) divertors [3] on most advanced tokamaks such as TCV [4], NSTX [5] and DIII-D [6]. In 2014, we also demonstrated the effects of applying QSF plasma shape [7]. It was found that in L-mode case the peak heat flux to the divertor target can be effectively reduced to at least by a factor of 1/2.…”

“…1, is negligible after SMBI was turned on. It is proving in reference [7] if controlling the plasma shape to the lower single null quasi-snowflake shape (LQSF), the peak heat load can be reduced to the level of a factor below 1/2 in comparision to the conventianl SN diverted plasma configuration. We further extended this operation to exactly control the shape.…”

Design and simulation of the snowflake divertor control for NSTX–U

“…Additional properties of the configuration include a significantly longer X-point connection length, leading to an increase in the temperature drop and radiative losses in the SOL, and the presence of additional strike points across which the power exhaust can be partitioned. In recent years, the SFD has been the subject of investigations on several devices [22][23][24][25][26][27][28][29], all of which have provided experimental confirmation of many favorable properties of the configuration. In particular, the SFD was integrated into H-mode scenarios on NSTX (prior to the upgrade).…”

Advances in experimental research towards high confinement and steady state operation on the Experimental Advanced Superconducting Tokamak

“…(6) EAST开展了具备良好热负荷分散功能的稳态 准雪花偏滤器磁面位形放电实验, 成功获得了长脉冲 无ELM高约束等离子体, 并有效地实现了热流分散, 显著降低了偏滤器靶板的峰值热负荷 [54] . (7) EAST研制了环向模数n可以达到4的ITER类 型的共振磁扰动(RMP)系统.…”