Experimental and simulation study of impurity transport response to RMPs in RF-heated H-mode plasmas at EAST

Abstract

Spatial profiles of impurity emission measurements in the extreme ultraviolet (EUV) spectroscopic range in radiofrequency (RF)-heated discharges are combined with one-dimensional and three-dimensional transport simulations to study the effects of resonant magnetic perturbations (RMPs) on core impurity accumulation at EAST. The amount of impurity line emission mitigation by RMPs appears to be correlated with the ion Z for lithium, carbon, iron and tungsten monitored, i.e. stronger suppression of accumulation for heavier ions. The targeted effect on the most detrimental high-Z impurities suggests a possible advantage using RMPs for impurity control. Profiles of transport coefficients are calculated with the STRAHL one-dimensional impurity transport code, keeping $\nu /D$ fixed and using the measured spatial profiles of $\textrm{F}{\textrm{e}^{20 + }}$ , $\textrm{F}{\textrm{e}^{21 + }}$ and $\textrm{F}{\textrm{e}^{22 + }}$ to disentangle the transport coefficients. The iron diffusion coefficient ${D_{\textrm{Fe}}}$ increases from $1.0- 2.0\;{\textrm{m}^2}\;{\textrm{s}^{ - 1}}$ to $1.5- 3.0\;{\textrm{m}^2}\;{\textrm{s}^{ - 1}}$ from the core region to the edge region $(\rho \gt 0.5)$ after the onset of RMPs. Meanwhile, an inward pinch of iron convective velocity ${\nu _{\textrm{Fe}}}$ decreases in magnitude in the inner core region and increases significantly in the outer confined region, simultaneously contributing to preserving centrally peaked $\textrm{Fe}$ profiles and exhausting the impurities. The ${D_{\textrm{Fe}}}$ and ${\nu _{\textrm{Fe}}}$ variations lead to reduced impurity contents in the plasma. The three-dimensional edge impurity transport code EMC3-EIRENE was also applied for a case of RMP-mitigated high-Z accumulation at EAST and compared to that of low-Z carbon. The exhaust of ${\textrm{C}^{6 + }}$ toward the scrape-off layer accompanying an overall suppression of heavier ${\textrm{W}^{30 + }}$ is observed when using RMPs.

Effect of edge magnetic island on carbon screening in the J-TEXT tokamak

“…Various studies have reported the transport change with edge magnetic island [13,14,19]. One idea is that the enhanced transport is due to the higher radial fraction of the parallel transport with the modified magnetic field topology.…”

“…Under the same regime, impurity behavior has also been found to be effectively affected by RMP on various devices [13][14][15]. It is widely reported that the impurity concentration is reduced with the introduction of RMP in both L-and H-mode plasma.…”

“…The larger diffusion coefficient D∼5-10 m 2 s −1 is also favorable for reducing impurity concentration. In EAST H-mode plasmas, the RMPs increase the diffusion coefficient and the outward convective velocity through the STRAHL simulation for iron spectra (Fe 20+ 12.88 nm, Fe 21+ 11.63 nm, Fe 22+ 13.29 nm) [13].…”

Space-resolved vacuum-ultraviolet spectroscopy for measuring impurity emission from divertor region of EAST tokamak

“…Therefore, the measurement of the impurity radiation and profile near the X-point is also very important for stable radiative divertor operations. In addition, previous studies have shown that RMP is an effective way to suppress impurity accumulation in the plasma [4,5]. According to the simulation results with impurity transport code EMC3-EIRENE, the impurity profile from the divertor area clearly changes as RMP is applied [6].…”

Evaluation of edge transport and core accumulation of tungsten for CFETR with EMC3-EIRENE and STRAHL

“…The impurity transport code STRAHL calculates the radial density and radiation distributions of impurity in the core plasma, which has been applied to many fusion devices, including AUG [43], TCV [44], ADITYA [45], HL-2A [46], EAST [47,48], DIII-D [49]. The STRAHL code solves a coupled impurity particle conservation equation for each ionization stage [50,51],…”