Study on ECH-assisted start-up using trapped particle configuration in KSTAR and application to ITER

Lee, Jeong‐Won; Kim, Jaewook; An, Younghwa; Yoo, Min-Gu; Hwang, Y.S.; Na, Yong-Su

doi:10.1088/1741-4326/aa8511

Cited by 13 publications

(16 citation statements)

References 21 publications

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“…2017; Lee et al. 2017). A study of breakdown experiments driven by radio frequency has also been done and combined with a one-point model to study the effects of magnetic structure (Yoneda et al.…”

Section: Introductionmentioning

confidence: 99%

“…On the breakdown modes and parameter space of ohmic tokamak start-up 3 pre-ionization scheme using a trapped particle configuration has been developed with low loop voltage and low volt-second consumption (An et al 2017;Lee et al 2017). A study of breakdown experiments driven by radio frequency has also been done and combined with a one-point model to study the effects of magnetic structure (Yoneda et al 2017).…”

Section: Introductionmentioning

confidence: 99%

“…A theoretical analysis (Farina 2017) using EC assisted pre-ionization has been done and it showed that cold electrons can easily gain energies well above the ionization energy in most conditions, which have been observed experimentally on DIII-D (Jackson et al 2010a) and FTU (Granucci et al 2015). Recently, an electron cyclotron heating (ECH) pre-ionization scheme using a trapped particle configuration has been developed with low loop voltage and low volt-second consumption (An et al 2017;Lee et al 2017). A study of breakdown experiments driven by radio frequency has also been done and combined with a one-point model to study the effects of magnetic structure (Yoneda et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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On the breakdown modes and parameter space of ohmic tokamak start-up

et al. 2018

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Tokamak start-up is strongly dependent on the state of the initial plasma formed during plasma breakdown. We have investigated through numerical simulations the effects that the pre-filling pressure and induced electric field have on pure ohmic heating during the breakdown process. Three breakdown modes during the discharge are found, as a function of different initial parameters: no breakdown mode, successful breakdown mode and runaway mode. No breakdown mode often occurs with low electric field or high pre-filling pressure, while runaway electrons are usually easy to generate at high electric field or low pre-filling pressure (${<}1.33\times 10^{-4}$ Pa). The plasma behaviours and the physical mechanisms under the three breakdown modes are discussed. We have identified the electric field and pressure values at which the different modes occur. In particular, when the electric field is $0.3~\text{V}~\text{m}^{-1}$ (the value at which ITER operates), the pressure range for possible breakdown becomes narrow, which is consistent with Lloyd’s theoretical prediction. In addition, for $0.3~\text{V}~\text{m}^{-1}$, the optimal pre-filling pressure range obtained from our simulations is $1.33\times 10^{-3}\sim 2.66\times 10^{-3}$ Pa, in good agreement with ITER’s design. Besides, we also find that the Townsend discharge model does not appropriately describe the plasma behaviour during tokamak breakdown due to the presence of a toroidal field. Furthermore, we suggest three possible operation mechanisms for general start-up scenarios which could better control the breakdown phase.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the breakdown modes and parameter space of ohmic tokamak start-up

et al. 2018

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“…Recently, it was found that the TPC was beneficial not only for non-inductive I p start-up, but also for ECW assisted inductive I p start-up [24], [25]. The effect of the poloidal field configuration on ECW assisted Ohmic start-up was studied further in TST-2, with focus on the difference between the TPC and the FNC in the high ECW power and low-pressure regime [26].…”

Section: Optimization Of Inductive Plasma Current Ramp-upmentioning

confidence: 99%

Overview of coordinated spherical tokamak research in Japan

et al. 2022

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Spherical tokamak (ST) research in Japan has produced many innovative results: (i) plasma start-up to I p > 70 kA was achieved by electron cyclotron wave (ECW) with N ∥ = 0.75, while electron heating to T e > 500 eV was achieved with N ∥ = 0.26 on QUEST. (ii) The radiofrequency (RF)-induced transport model was combined with the x-ray emission model, and extended magnetohydrodynamics equilibrium with kinetic electrons was developed to interpret fast-electron-dominated lower hybrid wave sustained plasmas on TST-2. (iii) Density as high as 30 times the cutoff density was achieved by electron Berstein wave current drive combined with electron beam injection on LATE. (iv) Multiple plasmoids formed by tearing instability in the elongated current sheet were observed, and flux closure and ion heating by plasmoid-mediated fast magnetic reconnection were observed on HIST. (v) Optimization of ECW-assisted inductive start-up with a vertical field with positive decay index was performed on TST-2. (vi) Stabilization of the vertical displacement event by a set of upper and lower helical field coils was demonstrated on TOKASTAR-2. (vii) A 6 h discharge was achieved by cool-down of the center stack cover on QUEST, where the plasma duration limit was consistent with the wall saturation time estimated by modeling. (viii) Extension of ion heating by plasma merging was achieved on TS-3U, TS-4U, UTST, MAST, and ST40.

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“…The TPC start-up saved volt-second consumption and extended lower pressure limit compared with the FNC. The second harmonic EC-assisted Ohmic startup with the TPC was also shown to have a wider pressure window for successful start-up on KSTAR [17].…”

Section: Introductionmentioning

confidence: 96%

Optimization of Poloidal Field Configuration for Electron Cyclotron Wave Assisted Low Voltage Ohmic Start-Up in TST-2

Tsujii

Takase

et al. 2021

Plasma and Fusion Research

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We investigated electron cyclotron (EC) wave assisted low voltage Ohmic start-up in the conventional field null configuration (FNC) and the trapped-particle configuration (TPC) in the TST-2 spherical tokamak device. The upper pressure limit for successful burn-through increased when EC power was applied for both the FNC and TPC. On the other hand, at low prefill pressure, breakdown was delayed in the FNC start-up. The achievable plasma current also decreased especially at high EC power. By applying the TPC, fast breakdown was recovered even at high EC power. The plasma current ramp-up rate was also greater with TPC compared with FNC at the same loop voltage waveform. The lower prefill pressure limit for successful breakdown expanded in the TPC compared to that in the FNC. The higher vertical field decay index resulted in faster EC breakdown. The reduction of the upper pressure limit due to impurities was the same in the FNC and TPC indicating that the poloidal field configuration did not significantly affect the upper pressure limit for successful burn-through.

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Study on ECH-assisted start-up using trapped particle configuration in KSTAR and application to ITER

Cited by 13 publications

References 21 publications

On the breakdown modes and parameter space of ohmic tokamak start-up

On the breakdown modes and parameter space of ohmic tokamak start-up

Overview of coordinated spherical tokamak research in Japan

Optimization of Poloidal Field Configuration for Electron Cyclotron Wave Assisted Low Voltage Ohmic Start-Up in TST-2

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