Integration of full divertor detachment with improved core confinement for tokamak fusion plasmas

Abstract

Divertor detachment offers a promising solution to the challenge of plasma-wall interactions for steady-state operation of fusion reactors. Here, we demonstrate the excellent compatibility of actively controlled full divertor detachment with a high-performance (βN ~ 3, H98 ~ 1.5) core plasma, using high-βp (poloidal beta, βp > 2) scenario characterized by a sustained core internal transport barrier (ITB) and a modest edge transport barrier (ETB) in DIII-D tokamak. The high-βp high-confinement scenario facilitates divertor detachment which, in turn, promotes the development of an even stronger ITB at large radius with a weaker ETB. This self-organized synergy between ITB and ETB, leads to a net gain in energy confinement, in contrast to the net confinement loss caused by divertor detachment in standard H-modes. These results show the potential of integrating excellent core plasma performance with an efficient divertor solution, an essential step towards steady-state operation of reactor-grade plasmas.

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

“…Injection of the impurity in the divertor helped to trigger the formation of an internal transport barrier at large radius in the core density, and both electron and ion temperature profiles, compensating for the reduction in pedestal pressure and enhancing the performance parameters to H 98y2 = 1.5, β N = 3, β p > 2, at q 95 = 7.8. In separate high β p experiments, large radius ITBs were also obtained with strong deuterium gas injection [52,53]. The high β p configuration lends itself to ITB formation due to a combination of Shafranov shift stabilization of turbulence, high bootstrap current generation at high q 95 and high q min at large radius [54].…”

“…Integration of a high-performance core plasma and a low temperature solution for the plasma at the divertor targets has been demonstrated in a high poloidal beta scenario that features large Shafranov shift, internal transport barriers (ITBs) in n e , T e and T i coupled to a detached divertor using active feedback-controlled N 2 or Ne puffing [50][51][52][53][54]. Theory-based modeling suggests that similar plasmas in ITER FPO phase with planned heating systems could be consistent with Q = 10 at reduced plasma current of 7-9 MA [51].…”

“…Theory-based modeling suggests that similar plasmas in ITER FPO phase with planned heating systems could be consistent with Q = 10 at reduced plasma current of 7-9 MA [51]. In the DIII-D experiments, feedback control of either nitrogen or neon was used to control the degree of detachment of the divertor while coupling to a high-performance core plasma at high poloidal beta (nitrogen case shown in figure 12) [50,52,53]. This example shows the characteristics of the core-edge coupling achieved with either nitrogen or neon impurity seeding.…”

“…This example shows the characteristics of the core-edge coupling achieved with either nitrogen or neon impurity seeding. With High β p scenario: with nitrogen injection (dashed line) (a) pedestal pressure (black) and central pressure (red), (b) nitrogen gas rate (blue) and I sat /I roll ratio (red) vs target values (black), (c) target ion saturation current (red) and target T e (black) and Reproduced from [52]. CC BY 4.0.…”

Recent progress in Chinese fusion research based on superconducting tokamak configuration

“…These modules have excellent compatibility with high core plasma performance, which has also been demonstrated on Doublet III D (DIII-D) in 2019. 56 In terms of the particle exhaust, including fueling and impurity particles in addition to wall conditioning and impurity source control, the efficiency of the particle flux exhaust is optimized by making full use of the divertor closure and the plasma drifts in the scrape-off layer and divertor volume. For wall conditioning, many advanced methods have been developed and employed in the EAST, including first wall baking, direct-current glow discharge cleaning (DC-GDC), high-frequency GDC (HF-GDC), ICRF discharge cleaning (ICRF-DC), silicon coating (SiD4), lithium coating, and real-time lithium powder injection (LPI) during plasma operation.…”