Study of Plasma Equilibrium Control for JT-60SA using MECS

Miyata, Yasumitsu; Suzuki, Takahiro; Ide, S.; Urano, H.

doi:10.1585/pfr.9.3403045

Cited by 16 publications

(12 citation statements)

References 6 publications

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“…The TOSCA code [4] has been employed to design the preprogrammed magnetic control sequence for creating the magnetic null configuration and initial target equilibrium. The subsequent I p ramp-up and equilibrium control (in the present scenario, after 0.33 s) have been simulated using the MECS code [47][48][49] and the integrated transport code TOPICS [50]. One of the purposes of the present work is to confirm the consistencies of the startup scenario prepared by the above separate codes, concerning the plasma power balance, I p rampup rate, breakdown and burn-through times, and evolution of the plasma parameters.…”

Section: Magnetic Control Scenario For Plasma Startupmentioning

confidence: 86%

Modelling of ohmic startup and runaway electron formation in support of JT-60SA initial operation

Matsuyama¹,

Wakatsuki²,

Inoue³

et al. 2022

Nucl. Fusion

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The plasma startup with ITER-relevant sub-mPa neutral pressures in the JT-60SA superconducting tokamak is studied using a zero-dimensional (0D) power balance model for the plasma burn-through phase. In the ohmic startup scenario assumed here, the lower limit of the operational neutral pressure is determined by the condition for the Townsend avalanche at a high $E/p$ limit, whereas the upper limit depends on the available ohmic heating power for the burn-through with the base Power Supply (PS) of the superconducting coils, corresponding to 0.2-0.3 V/m. The operational conditions that lead to RE generation are evaluated to mitigate the risk of RE discharges. The simulation shows that startup REs are generated during the temperature rise immediately after the burn-through under relatively low-density conditions, and then the RE current value is gradually increased in balance with the RE loss processes on the timescale of $I_p$ ramp-up. Therefore, it is expected that REs can be avoided or mitigated if the electron density during the early build-up phase is tuned by a combination of prefill gas and additional fuelling. However, a startup with an excessive prefill gas will lose the margin of the density control, and a full RE discharge can be triggered when the plasma burn-through fails owing to a high concentration of impurities such as oxygen, if the operational point is marginal to the burn-through limit. The present modelling work implies that preparing the operation with sufficient margins against the failure of impurity burn-through is important for mitigating the risk of unintended plasma termination. Although the carbon wall environment may have a lower risk of RE generation, to alleviate the operational uncertainties of the new device, strategies for expanding the operational window are also discussed in support of JT-60SA initial operation.

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Section: Magnetic Control Scenario For Plasma Startupmentioning

confidence: 86%

Modelling of ohmic startup and runaway electron formation in support of JT-60SA initial operation

Matsuyama¹,

Wakatsuki²,

Inoue³

et al. 2022

Nucl. Fusion

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“…We introduce an 'AVA gain' to measure a saturation level of the power supplies voltage for P/S and I p control. Our magnetohydrodynamics equilibrium control simulator (MECS) [8][9][10] successfully achieved the higher κ in comparison with the conventional scheme by virtue of the AVA scheme [7]. The improvement of the accessible κ by the AVA scheme indicates that the equilibrium controller performance affects the VI controllability.…”

Section: Introductionmentioning

confidence: 92%

A new vertical instability predictor via precursor oscillation detection with performance monitoring of equilibrium controller

Inoue¹,

Miyata²,

Urano³

et al. 2022

Nucl. Fusion

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We first propose an accurate and robust vertical instability (VI) predictor by using a support vector machine (SVM), one of the machine learning methods. The SVM is trained to detect precursor oscillation by using newly introduced classification parameters to measure the equilibrium controller performance, which is obtained by the adaptive voltage allocation scheme [S. Inoue, Y. Miyata, H. Urano, T. Suzuki, Nuclear Fusion 61 (9) (2021) 096009]. Furthermore, multi-layered preprocessing filters are newly introduced for the SVM training/prediction, which improves the prediction accuracy under highly imbalanced conditions, where ∼ 500 disruptive data while ∼ 3 × 10^6 non-disruptive data. The classification parameters can be calculated only by the current centroid, which suggests that the proposed predictor is robust against the extrapolation for the experiment and will be validated in JT-60SA experiments.

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“…Before introducing the developed control scheme, let us introduce our MHD equilibrium control simulator 'MECS', which is basically a summary of [8][9][10] and is utilized throughout this paper to test the controllability of the developed scheme.…”

Section: Overviewmentioning

confidence: 99%

“…In MECS, the equilibrium controller outputs the power supply voltages for active conducting coils, with which the circuit equations and the free-boundary Grad-Shafranov equation are iteratively solved until I p , β p , l i , and Ψ convergence. Consequently, the equilibrium control is self-consistently performed in MECS with the realistic disturbances and the limits of coils and power supplies and in the presence of the VDE/HDE [10].…”

Section: Overviewmentioning

confidence: 99%

Development of JT-60SA equilibrium controller with an advanced ISO-FLUX control scheme in the presence of large eddy currents and voltage saturation of power supplies

et al. 2021

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An advanced ISO-FLUX equilibrium control scheme is developed and implemented in the JT-60SA equilibrium controller. For future fusion reactor, the VDE control by the active superconducting coils is essential due to the absence of in-vessel coils and stabilization plates, and the presence of large gap between plasmas and vacuum vessels with the tritium breeding blanket. Under the circumstances, the equilibrium controller should achieve plasma position/shape control and plasma current control by superconducting coils within limited power supply voltages, where plasma current control affects plasma position/shape control, and vice versa. The newly developed ISO-FLUX control scheme enhances the controllability under the above hybrid control of position/shape and plasma current circumstances. Furthermore, the new scheme also provides good controllability under large eddy currents conditions, which will also be expected in future superconducting tokamaks, such as JT-60SA, ITER, and DEMO due to its large inductance and high target plasma current. The JT-60SA equilibrium controller with the developed scheme is well verified by a magnetohydrodynamic equilibrium control simulator ‘MECS’ and ready for the integrated commissioning of JT-60SA.

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Study of Plasma Equilibrium Control for JT-60SA using MECS

Cited by 16 publications

References 6 publications

Modelling of ohmic startup and runaway electron formation in support of JT-60SA initial operation

Modelling of ohmic startup and runaway electron formation in support of JT-60SA initial operation

A new vertical instability predictor via precursor oscillation detection with performance monitoring of equilibrium controller

Development of JT-60SA equilibrium controller with an advanced ISO-FLUX control scheme in the presence of large eddy currents and voltage saturation of power supplies

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