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

Inoue, Shizuo; Miyata, Yasumitsu; Urano, H.; Suzuki, Tsuneo

doi:10.1088/1741-4326/ac1260

Cited by 13 publications

(40 citation statements)

References 27 publications

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“…New plasma experiments using the JT-60SA superconducting tokamak [2] will make key contributions to this field. To prepare for the initial tokamak operation at JT-60SA [3], magnetic field control scenarios were designed to satisfy the breakdown condition based on the Townsend model [4] and the equilibrium shape and plasma current controller was developed to allow reliable VDE control [5].…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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%

“…We note that the VI control under these kinds of conditions is significantly severe in comparison with that of present-day conducting and/or moderate size tokamaks. An improvement of the conventional control scheme is required, for which we developed a novel control scheme, namely an adaptive voltage allocation (AVA) scheme [7]. We introduce an 'AVA gain' to measure a saturation level of the power supplies voltage for P/S and I p control.…”

Section: Introductionmentioning

confidence: 99%

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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“…We developed a plasma equilibrium controller using MHD equilibrium control simulator (MECS) [26][27][28]. The MECS code simulates the time evolution of plasma equilibrium with electro-magnetic interactions with coils and passive conducting structures under the constraints of the power supply specification.…”

Section: Plasma Equilibrium Controlmentioning

confidence: 99%

“…The MECS code simulates the time evolution of plasma equilibrium with electro-magnetic interactions with coils and passive conducting structures under the constraints of the power supply specification. A novel control scheme, namely an adaptive voltage allocation (AVA) scheme [28], has been developed to achieve highly elongated plasmas stably not only for JT-60SA, but also for ITER and DEMO, where vertical displacement events (VDEs) as a part of the position and shape control should be controlled actively by the superconducting poloidal coil system, within the limitations of temporal controllability. In such situations, the position/shape control and the I p control influence each other within the power supply voltage limits, and thus a disturbance of the I p degrades the VDE controllability and diminishes the accessible elongation (κ X ).…”

Section: Plasma Equilibrium Controlmentioning

confidence: 99%

Completion of JT-60SA construction and contribution to ITER

et al. 2022

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Construction of the JT-60SA tokamak was completed on schedule in March 2020. Manufacture and assembly of all the main tokamak components satisfied technical requirements, including dimensional accuracy and functional performances. Development of the plasma heating systems and diagnostics have also progressed, including the demonstration of the favourable electron cyclotron range of frequency (ECRF) transmission at multiple frequencies and the achievement of long sustainment of a high-energy intense negative ion beam. Development of all the tokamak operation control systems has been completed, together with an improved plasma equilibrium control scheme suitable for superconducting tokamaks including ITER. For preparation of the tokamak operation, plasma discharge scenarios have been established using this advanced equilibrium controller. Individual commissioning of the cryogenic system and the power supply system confirmed that these systems satisfy design requirements including operational schemes contributing directly to ITER, such as active control of heat load fluctuation of the cryoplant, which is essential for dynamic operation in superconducting tokamaks. The integrated commissioning (IC) is started by vacuum pumping of the vacuum vessel and cryostat, and then moved to cool-down of the tokamak and coil excitation tests. Transition to the super-conducting state was confirmed for all the TF, EF and CS coils. The TF coil current successfully reached 25.7 kA, which is the nominal operating current of the TF coil. For this nominal toroidal field of 2.25 T, ECRF was applied and an ECRF plasma was created. The IC was, however, suspended by an incident of over current of one of the superconducting equilibrium field coil and He leakage caused by insufficient voltage holding capability at a terminal joint of the coil. The unique importance of JT-60SA for H-mode and high-β steady-state plasma research has been confirmed using advanced integrated modellings. These experiences of assembly, IC and plasma operation of JT-60SA contribute to ITER risk mitigation and efficient implementation of ITER operation.

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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

Cited by 13 publications

References 27 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

Completion of JT-60SA construction and contribution to ITER

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