I-mode investigation on the Experimental Advanced Superconducting Tokamak

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Sixty-five discharges have been confirmed as I-mode discharges after searching the EAST database from 2016 to 2018, and some additional I-mode discharges were obtained in 2019. The I-mode regime features no edge localized modes (ELMs), high energy confinement, and a steep temperature pedestal, while particle confinement remains at L-mode levels. The I-mode regime has been obtained over a small parameter space (B T = 2.4 -2.7 T, I p = 0.4 -0.6 MA, q 95 = 4 -6) using a configuration with B × ▽B drift away from the active X-point. Most of the discharges in EAST are dominated by lower hybrid wave (LHW) heating. In addition, some are heated with both LHW and neutral beam injection (NBI) heating, and a few discharges are heated by NBI and electron cyclotron resonance heating (ECRH). Turbulence suppression in density perturbation has been defined as signaling the onset of the L-I transition. The power threshold of the I-mode is slightly larger than that of the 2008 ITPA scaling law of H-mode. The minimum L-I power threshold varies only weakly with B T , and the power range for the I-mode increases with increasing B T . The I-mode is superior to the L-mode in terms of energy confinement but is still slightly inferior to the H-mode under similar conditions, although the energy confinement time decreases more slowly with increasing heating power than it does in the typical H-mode case. NBI has some benefit for achieving higher confinement. The I-mode is very sensitive to the density near the edge. Under a constant high heating power, a small enhancement in the density will terminate the I-mode, sometimes leading to the I-H transition.

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Power threshold and confinement of the I-mode in the EAST tokamak

Liu

et al. 2020

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“…The I-mode operation regime on EAST [12] has been widely achieved in D plasma in the unfavorable B T divertor configuration (B × ∇B directed away from the active X-point), where the L-H transition threshold power is significantly higher and the energy confinement is much worse than those at the favorable configuration [13]. The access to the I-mode regime in D plasma on EAST was found to be independent from the heating method and wall material.…”

Section: Introductionmentioning

confidence: 98%

I-mode operation in helium plasma with pure radio frequency wave heating and ITER-like tungsten divertor on EAST

Zhang¹,

Gong²,

Qian³

et al. 2021

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The characteristics of I-mode operation in helium (He) plasma with radio-frequency (RF) wave heating and ITER-like tungsten divertor have been investigated for the first time on EAST, under the favorable B T configuration. Stationary I-mode in He plasma lasting for ∼5.4 s was achieved at I p = 0.5 MA, B T = 2.4 T with a total injected RF power of 3.5 MW, along with the appearance of the 30–90 kHz weakly coherent mode and the ∼13 kHz edge temperature ring oscillation. The pulse length was only limited by the heating power duration. He concentration was found to play a critical role in I-mode operation, as L–I transition threshold power was increased and the energy confinement was degraded with increasing He concentration. The experimental investigation result on energy confinement and divertor heat flux between I- and H-mode plasma was also given at a similar He concentration.

“…Besides some external means that can be adopted to actively control the turbulence, the ideal approach is to make use of some internally self-excited plasma modes that have the capability to regulate the turbulence level. Geodesic acoustic modes (GAMs) and low frequency zonal flows (LFZFs) are indeed such types of modes that are commonly self-excited in L-mode plasmas on almost all tokamaks, and in I-mode plasmas on some tokamaks [1][2][3]. This is the main reason that people are interested in GAMs and LFZFs.…”

Section: Introductionmentioning

confidence: 99%

A gyro-fluid model of global geodesic acoustic modes supported by finite ion Larmor radius

Wang¹,

Zhou²,

Wang³

2022

A theory of global geodesic acoustic modes with short wavelengths based on the framework of an electrostatic gyro-fluid has been developed, in which the more thorough sorts of finite-ion-Larmor-radius effects are encompassed than in the two-fluid model (Wang et al 2021 Nucl. Fusion 61 106024), while the radial differential equation of the eigenmodes still comes up in a compact and analytically tractable form. By solving the corresponding boundary value problem numerically with typical equilibrium profiles, a multitude of global geodesic acoustic modes with quantized eigen-frequencies have been found. In particular, as the consequence of the plasma model improvement, we have obtained multiple edge-localized global geodesic acoustic modes with the features resembling those observed experimentally.