Multivariable non-interacting control of plasma configuration in JT-60U

Yoshino, R.

doi:10.1016/0920-3796(94)90003-5

Cited by 10 publications

(7 citation statements)

References 8 publications

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“…In tokamaks the feedback control of the plasma current is indispensable for maintaining the plasma confinement and is planned for ITER [25]. Multivariable non-interacting control of poloidal field coil currents is demonstrated in JT-60U [26], and it can also be applied for ITER and tokamak reactors. Thus, when the plasma current is kept constant or varied at a constant rate, the deviation of the plasma current from the reference value can be used as a precursor of the major disruption.…”

Section: 34mentioning

confidence: 99%

Neural-net disruption predictor in JT-60U

Yoshino

2003

Nucl. Fusion

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The prediction of major disruptions caused by the density limit, the plasma current ramp-down with high internal inductance li, the low density locked mode and the β-limit has been investigated in JT-60U. The concept of ‘stability level’, newly proposed in this paper to predict the occurrence of a major disruption, is calculated from nine input parameters every 2 ms by the neural network and the start of a major disruption is predicted when the stability level decreases to a certain level, the ‘alarm level’. The neural network is trained in two steps. It is first trained with 12 disruptive and six non-disruptive shots (total of 8011 data points). Second, the target output data for 12 disruptive shots are modified and the network is trained again with additional data points generated by the operator. The ‘neural-net disruption predictor’ obtained has been tested for 300 disruptive shots (128 945 data points) and 1008 non-disruptive shots (982 800 data points) selected from nine years of operation (1991–1999) of JT-60U. Major disruptions except for those caused by the β-limit have been predicted with a prediction success rate of 97–98% at 10 ms prior to the disruption and higher than 90% at 30 ms prior to the disruption while the false alarm rate is 2.1% for non-disruptive shots. This prediction performance has been confirmed for 120 disruptive shots (56 163 data points), caused by the density limit, as well as 1032 non-disruptive shots (1004 611 data points) in the last four years of operation (1999–2002) of JT-60U. A careful selection of the input parameters supplied to the network and the newly developed two-step training of the network have reduced the false alarm rate resulting in a considerable improvement of the prediction success rate.

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Section: 34mentioning

confidence: 99%

Neural-net disruption predictor in JT-60U

Yoshino

2003

Nucl. Fusion

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“…which is solved for the vertical coil current waveform I v fitted to the experimental result (I VALL in figure 8(b)): I V (t) = 8669 + {38.541 + 18747(t − 6.041) − 25713(t − 6.041) 2 − 1739.1(t − 6.041) 3 + 43386(t − 6.041) 4 − 50551(t − 6.041) 5 + 27878(t − 6.041) 6 + 8313.5(t − 6.041) 7 + 1288.2(t − 6.041) 8 − 81.241(t − 6.041) 9 } (4.…”

Section: The Plasma Current Ramp-up In Jt-60u By Nbi and Vertical Fieldunclassified

“…where l k = {(1+κ 2 )/2} 0.5 , l i is the internal inductance and κ is the elongation. The equilibrium vertical field B VE for keeping the plasma at the centre R, which is moved outward from the geometrical centre due to the Shafranov shift [5], is given by…”

Section: Introductionmentioning

confidence: 99%

“…However, detailed studies of the vertical field effect on the plasma current ramp-up have not been conducted in a high aspect ratio tokamak until the author's recent proposal for the plasma current ramp-up by the vertical field in a ST reactor [4]. On the other hand, the coupling problems between the OH transformer and vertical field coils, such as association between the plasma position movement and plasma current, have been experimentally studied and controlled in JT-60U [5,9,10]. In their experiments, non-interacting multi-variable control between the OH transformer and vertical coils has been developed and it is clearly demonstrated that the vertical field to control the plasma position can induce the plasma current.…”

Section: Introductionmentioning

confidence: 99%

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Plasma current ramp-up assisted by outer vertical field coils in a high aspect ratio tokamak

Mitarai

Yoshino²,

Ushigusa³

2002

Nucl. Fusion

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Plasma current ramp-up assisted by outer vertical field coils with non-inductively driven current is studied during the ignition access phase in a high aspect ratio tokamak such as ITER-FEAT class tokamak reactor. In a tokamak without the Ohmic transformer, the pl1asma current ramp-up to 8 MA could be achieved by the vertical field with the heating/current drive power of 100 MW. The current ramp-up time can be chosen arbitrarily, as shorter than that expected in the usual, non-inductive current drive operation analyses, and it depends on the fusion power ramp-up time. This makes the reactor operation flexible. Experimental evidence showing the current drive by a vertical field in JT-60U has also been presented with plasma circuit theory.

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“…Therefore, the operation is simpler than the first method, even during the flat-top phase, because vertical field control does not depend on the ohmic transformer current. This second method has been used in ASDEX Upgrade [18], DIII-D [19], JT-60U [20], TRIAM-1M [21], TST-2 [22], and Globus-M [23], and will be used in the SST-1 [24] and KTM [25] tokamaks.…”

Section: Introductionmentioning

confidence: 99%

First Ohmic Discharge Assisted with RF Power in QUEST Spherical Tokamak

Mitarai

Nakamura

Tashima

et al. 2011

Plasma and Fusion Research

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Ohmic plasma currents of up to 17 kA with a discharge duration of 0.32 s have been obtained in the Kyushu University Experiment with Steady-State Spherical Tokamak (QUEST) with the help of electron cyclotron wave (ECW) and cancellation coils (CCs). The CCs, originally installed to create a field null in the plasma breakdown phase, are essential for producing plasma current in QUEST. Although the ohmic coil current is initially biased and then reduced completely to zero to induce the plasma current in 15-20 ms, we demonstrate that the flat top of the plasma current exceeding 20 ms is maintained by the vertical field after the ohmic current is switched off. This type of operation is quite favorable for extending pulsed operation to the steady state by electron Bernstein wave current drive (EBCD).

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Multivariable non-interacting control of plasma configuration in JT-60U

Cited by 10 publications

References 8 publications

Neural-net disruption predictor in JT-60U

Neural-net disruption predictor in JT-60U

Plasma current ramp-up assisted by outer vertical field coils in a high aspect ratio tokamak

First Ohmic Discharge Assisted with RF Power in QUEST Spherical Tokamak

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