Identification of I-mode with ion ITB in NBI-heated plasmas on the HL-2A tokamak

Abstract

I-mode has been observed on the HL-2A tokamak. The I-mode features an edge transport barrier (ETB) in electron temperature and an L-mode like edge density. A weakly coherent mode (WCM) is observed in the edge region with the frequency of f ~ 60 - 160 kHz and the poloidal wavenumber of kθ ~ 0.5 - 2.5 cm-1. The maximum of WCM amplitude is located near the top of electron temperature pedestal. A critical value of E×B velocity shear for triggering the L-I transition has been found, and is much lower than that for triggering the L-H transition. Additionally, ion internal transport barrier (ITB) has been observed in the I-mode. The formation of ion ITB is due to the increase of E×B velocity shear, leading to the suppression of turbulence. Transport analysis further confirms the existence of electron ETB and ion ITB. The coexistence of electron ETB and ion ITB leads to an improved plasma confinement, which is comparable to that in the H-mode, suggesting that I-mode with ITB regimes could be an interesting operation scenario for future fusion devices.

Characteristics of edge temperature ring oscillation during the stationary improved confinement mode in EAST

“…This result could not be clarified by the current theoretical dispersion relation of a kinetic GAM. (9) The ETRO frequency decreases quickly and ultimately reaches LCO frequency as the I-mode transitions to the Hmode, with increasing T ped e and decreasing ν * e (figure 14), indicating that collisional damping also plays a significant role during I-H transition.…”

“…Although the high-confinement mode (H-mode) [1] has been considered as the baseline operational scenario for the International Thermonuclear Experimental Reactor (ITER) [2], the heat load caused by large edge localized modes (ELMs) due to relaxation of edge pressure and current is still one of the most crucial issues in fusion research [3]. An alternative improved confinement regime (the I-mode), featuring high energy confinement comparable to the H-mode and moderate particle confinement comparable to the L-mode [4], may be a possible solution, and has been widely investigated in various divertor tokamaks [5][6][7][8][9]. Generally, the I-mode is usually obtained under an unfavorable configuration, i.e.…”

Experimental and simulation analysis of Weakly Coherent Modes in I-mode discharges on EAST

“…One notable advantage of the I-mode is its stability to edge-localized modes (ELMs) as its pressure gradient does not reach the unstable range of peeling-ballooning modes [2]. The I-mode has been observed since the late 1990s [3,4] and has been studied across a wide range of parameters in various tokamaks, including ASDEX-Upgrade [5], Alcator C-Mod [6], DIII-D [7], EAST [8] and HL-2A [9]. Typically, the I-mode phase is achieved with an ion B×∇B drifting away from the active X-point, which is the unfavorable direction.…”

Experimental evidence for the drift wave nature of the weakly coherent mode in ASDEX Upgrade I-mode plasmas

“…I-mode is accessed in unfavorable drift configuration and has been achieved in a variety of tokamaks (Alcator C-Mod [2,3], ASDEX Upgrade (AUG) [1,4,5], DIII-D [6], EAST [7,8], HL-2A [9]) and with different heating schemes and magnetic fields. Although much research on the underlying physics of the transport channel separation was done, the results are still inconclusive.…”