Simulation study of mixed-impurity seeding with extension of integrated divertor code SONIC

Abstract

Aimed at obtaining key physics that determine the controllability of impurity transport in the scrape-off layer (SOL)/divertor regions, the integrated divertor code SONIC has been further extended to handle three or more impurity species kinetically. The extended SONIC code has been applied to the steady-state high-beta scenario-like plasma of JT-60SA as a testbed. We first performed a Ne transport simulation on the fixed Ar-seeded background plasma. Different radiation power distribution along the magnetic field line was obtained between Ar and Ne. The Ar radiation is strong around the top region of the SOL, which is mainly due to the line radiation of highly charged Ar ions trapped by the thermal force. In contrast, the Ne radiation is strong around the high-field side near the X point, mainly due to the line radiation of Ne 7+ trapped by the balance between the thermal force and the frictional force with D + parallel flow. We performed a parametric survey of Ne seeding rate as a second step. The effects of Ne transport on the plasma are self-consistently computed. The Ne impurities are injected into the plasma with a fixed puff rate of Ar. Even a small Ne seeding rate of 0.02 Pa m 3 s −1 results in lower Ar radiation power in the SOL and core edge than in the Ar-only case. This is mainly due to the high D + parallel flow velocity towards the inner divertor in the Ar+Ne seeding case. The resultant frictional force transports the Ar impurities towards the inner divertor region. When the line radiation of Ne 7+ is switched off in the simulation, such high D + parallel flow cannot be seen. These results suggest that the line radiation of Ne 7+ has a key role for the high D + parallel flow. The results show the possibility of impurity transport control in the SOL by mixed-impurity seeding.

Development of a novel integrated model GOTRESS+ for predictions and assessment of JT-60SA operation scenarios including the pedestal

“…This problem is also linked to the scrape-off-layer plasma physics, which is a key component to determine the boundary condition at the plasma surface, as well as plasma-wall interactions [35,57]. The values at the plasma surface used in this work have been prescribed consistent with the previous work [57,58]. It has been reported that EPED1 predictions with the SOLPS boundary conditions in ITER are different from those with the fixed values used [59], obviously suggesting the importance of the coupling between the core and scrape-off-layer plasma modelings, as also shown in more recent work [18,35].…”

Transient analysis of high-Z impurity screening by additional injection of low-Z impurity using integrated divertor code SONIC

“…We have developed the time-controlling interface of data exchange between SOLDOR and IMPMC, as well as merging recent updates of IMPMC code, e.g. the multi-impurity handling updates [13,16], the backflow model [14], and the kinetic thermal force model [17,18] of IMPMC code into the time dependent version. The calculation step is controlled by the data exchange interval time ∆t.…”

“…The computational grid with the indication of the gas puff location for JT-60SA is shown in figure 2. The calculation parameters are the same as in [13]. The input power from the core-edge interface (CEI) P CEI is set to be P CEI = 23 MW and is equally distributed among D + ions and electrons.…”

“…To understand the impurity transport processes in Ar-only and Ar + Ne mixed seeding cases, we have extended the integrated divertor code SONIC [11,12] to handle multiple impurity species kinetically. The extended SONIC has been applied to a predictive simulation of steady state high-beta plasma of JT-60SA as a testbed [13]. The comparison of Ar-only and Ar + Ne mixed seeding on JT-60SA plasma by SONIC has shown that the additional injection of Ne into Ar-seeded plasma results in lower Ar density and radiation power in the SOL and core edge than in the Ar-only case,maintaining the peak divertor heat load at less than 10 MW m −2 .…”

Completion of JT-60SA construction and contribution to ITER

“…For simulations of the future evolution to W-PFC, the code SOLPS-ITER in a high-density H-mode scenario has been used, in order to assess the possibility of detached regimes with nitrogen seeding [41]. The reduction of divertor heat load by impurity seeding in the high-β steady-state scenario has been studied using the integrated divertor code SONIC [42]. It showed that a single impurity injection of Ar results in a high Ar density at the top of SOL plasma (case A in figure 25), leading to an increase of core Ar density.…”