Evidence of a turbulent ExB mixing avalanche mechanism of gas breakdown in strongly magnetized systems

Yoo, Min-Gu; Lee, Jeong‐Won; Kim, Young-Gi; Kim, Jaewook; Maviglia, F.; Sips, A. C. C.; Kim, Hyun-Tae; Hahm, T.S.; Hwang, Y.S.; Lee, Hae June; Na, Yong-Su

doi:10.1038/s41467-018-05839-5

Cited by 19 publications

(40 citation statements)

References 40 publications

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“…Close to the wall, there are hot plasma zones directly linked to the magnetic separatrices (see fig. 10 of [33]). Because of the low density, the plasma interacts strongly with the walls, by means of ExB drifts and secondarily of open magnetic field lines [33].…”

Section: Traditional Ohmic Start-up Of the Tokamakmentioning

confidence: 98%

“…10 of [33]). Because of the low density, the plasma interacts strongly with the walls, by means of ExB drifts and secondarily of open magnetic field lines [33]. This direct interaction with the walls lasts till the formation of closed magnetic surfaces and produces a lot of impurities, in particular during the burn-through phase.…”

Section: Traditional Ohmic Start-up Of the Tokamakmentioning

confidence: 98%

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Plasma-wall self-organization in magnetic fusion

Escande¹,

Sattin²,

Zanca³

2021

Nucl. Fusion

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This paper introduces the concept of plasma-wall self-organization (PWSO) in magnetic fusion. The basic idea is the existence of a time delay in the feedback loop relating radiation and impurity production on divertor plates. Both a zero and a onedimensional description of PWSO are provided. They lead to an iterative equation whose equilibrium fixed point is unstable above some threshold. This threshold corresponds to a radiative density limit, which can be reached for a ratio of total radiated power to total input power as low as 1/2. When detachment develops and physical sputtering dominates, this limit is progressively pushed to very high values if the radiation of non-plate impurities stays low. Therefore, PWSO comes with two basins for this organization: the usual one with a density limit, and a new one with density freedom, in particular for machines using high-Z materials. Two basins of attraction of PWSO are shown to exist for the tokamak during start-up, with a high density one leading to this freedom. This basin might be reached by a proper tailoring of ECRH assisted ohmic start-up in present middle-size tokamaks, mimicking present stellarator start-up. In view of the impressive tokamak DEMO wall load challenge, it is worth considering and checking this possibility, which comes with that of more margins for ITER and of smaller reactors.

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Section: Traditional Ohmic Start-up Of the Tokamakmentioning

confidence: 98%

Section: Traditional Ohmic Start-up Of the Tokamakmentioning

confidence: 98%

Plasma-wall self-organization in magnetic fusion

Escande¹,

Sattin²,

Zanca³

2021

Nucl. Fusion

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“…This implies the reduction of turbulence persisting in the plasma from the breakdown 79 . As the ITB location expands to , the uctuation is severely reduced implying stabilisation of turbulence.…”

Section: Analysis Of Core Itb Characteristicsmentioning

confidence: 99%

A sustained high-temperature fusion plasma regime facilitated by fast ions

Han

Park

Sung

et al. 2022

Nature

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We report a discovery of a fusion plasma regime suitable for commercial fusion reactor where the ion temperature was sustained above 100 million degree about 20 s for the rst time. Nuclear fusion as a promising technology for replacing carbon-dependent energy sources has currently many issues to be resolved to enable its large-scale use as a sustainable energy source. State-of-the-art fusion reactors cannot yet achieve the high levels of fusion performance, high temperature, and absence of instabilities required for steady-state operation for a long period of time on the order of hundreds of seconds. This is a pressing challenge within the eld, as the development of methods that would enable such capabilities is essential for the successful construction of commercial fusion reactor. Here, a new plasma con nement regime called fast ion roled enhancement (FIRE) mode is presented. This mode is realized at Korea Superconducting Tokamak Advanced Research (KSTAR) and subsequently characterized to show that it meets most of the requirements for fusion reactor commercialization. Through a comparison to other well-known plasma con nement regimes, the favourable properties of FIRE mode are further elucidated and concluded that the novelty lies in the high fraction of fast ions, which acts to stabilize turbulence and achieve steady-state operation for up to 20 s by self-organization. We propose this mode as a promising path towards commercial fusion reactors.

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“…2018; Yoo et al. 2018). It has been found that the self-electric field produced by charge separation plays a large role in plasma breakdown.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental studies (Sand, Waelbroeck & Waidmann 1973;Holly et al 1981;Lloyd & Edlington 1986;Yoshino & Seki 1997;Kajiwara et al 2005) revealed that the electric field can be smaller when using the assist heating or preionization methods. In recent decades, many further studies have been developed on plasma breakdown (Jiang et al 2016;Yoo et al 2017;Peng et al 2018;Yoo et al 2018). It has been found that the self-electric field produced by charge separation plays a large role in plasma breakdown.…”

Section: Introductionmentioning

confidence: 99%

Simulation study of the influences of beryllium on the tokamak start-up process

Peng,

Qiu,

Zhao

et al. 2023

J. Plasma Phys.

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Tokamak start-up is strongly dependent on the state of the initial plasma formed during plasma breakdown. To acquire a better understanding of the process and to estimate the influence of the impurity of beryllium on the ohmic heating tokamak start-up process, one-dimensional particle-in-cell coupled with a Monte Carlo collision method has been developed. The main aim is to investigate the plasma performance under various amounts of beryllium with different discharge parameters. Tokamak breakdown with the impurity of beryllium in the ohmic heating strategy has been simulated. The simulation results show that with the impurity of beryllium, the increase of plasma density is suppressed compared with the case without beryllium. The breakdown time is delayed by the impurity. Moreover, the successful breakdown has a much higher requirement on discharge parameters with a low electric field operational scenario, since in the low electric field discharge the influence of beryllium impurity is greater. As the plasma density increases, the effect of beryllium impurity on plasma becomes more critical. It indicates that impurities cannot be neglected in the high plasma density.

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Evidence of a turbulent ExB mixing avalanche mechanism of gas breakdown in strongly magnetized systems

Cited by 19 publications

References 40 publications

Plasma-wall self-organization in magnetic fusion

Plasma-wall self-organization in magnetic fusion

A sustained high-temperature fusion plasma regime facilitated by fast ions

Simulation study of the influences of beryllium on the tokamak start-up process

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