Stabilizing effects of enhanced resistivity due to lithium-conditioning on low-n edge localized modes in NSTX

Abstract

The stabilizing effects of enhanced edge resistivity on the low-n edge localized modes (ELMs) are reported for the first time in the context of ELM suppression in H-mode discharge due to lithium-conditioning in the National Spherical Torus Experiment (NSTX). Here n is the toroidal mode number. Linear stability analysis of the corresponding experimental equilibrium suggests that the change in the equilibrium plasma density profile alone due to lithium-conditioning may be insufficient for a complete suppression of ELMs. The enhanced resistivity due to the increased effective electric charge number Z eff after lithium-conditioning can account for additional stabilization effects that contribute to robust ELM suppression. Remarkably, such a stabilizing effect of enhanced edge resistivity on the low-n ELMs only exists when two-fluid effects are considered in the MHD model.

Stabilizing effect of enhanced resistivity on peeling-ballooning instabilities on EAST

“…In contrast, the calculations in the present work extend the resistive stabilization effect to the intermediate-n modes. The above results verify the universality of the resistive stabilization effect on PBMs, however, this stabilizing effect of enhanced resistivity in EAST appears weaker than that observed in NSTX, where the low-n modes are fully stabilized with increasing Z eff even for an ELMy case [20,21].…”

“…ELMy case [20,21]. Figure 5 shows the contour plots of perturbed pressure and perturbed R-component magnetic field of the most unstable mode (n = 10) for equilibrium 2.…”

“…One of the impurity effects is the reduction of main ion density by dilution, which is guessed to play a role in improving PB stability and confinement [11,14,15]. Besides the dilution effect, a recent linear stability analysis of NSTX equilibria with the initial-value NIMROD code reveals that the enhanced resistivity affected by Z eff could also provide an additional stabilizing effect on low-n edge localized modes [20,21].…”

Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

“…This finding constitutes a consistent explanation of the ELM suppression phenomenon in NSTX. The primary result of this new finding of resistive stabilisation has been reported briefly in a recent brief communication [14]. In this article, the complete analyses are presented, based on both the ideal single-and twofluid MHD models, and the two-fluid resistive MHD model using a Spitzer resistivity profile for a thorough comparison of the pre-lithium ELMy reference and with-lithium ELM-free H-mode cases.…”

Evaluation of ideal MHD mode stability of CFETR baseline scenario

“…The inclusion of resistivity profile is expected to make the numerical modeling more accurate for predicting the stability of CFETR baseline design. In a recent article, resistivity has been reported to have both stabilizing and destabilizing effects on ideal MHD edge localized modes [17]. The linear calculation in NIMROD has checked the stability of modes n = 1 − 10 after placing conducting wall at 1.2a and found modes n = 2 − 10 to be unstable, where the n = 1 mode is always stable (blue curve in Fig.…”