Plasma current sustainment after iron core saturation in the STOR-M tokamak

•Plasma current can be started up by small iron core without central solenoid.•Iron core removes central solenoid.•Plasma current can be maintained after iron core saturation.•Hysteresis curve shows the partial core saturation.•Image field from iron core is estimated during discharge.•Spherical toka...

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Bibliographic Details
Published in:Fusion engineering and design 2014-10, Vol.89 (9-10), p.2467-2471
Main Authors: Mitarai, O., Ding, Y., Hubeny, M., Lu, Y., Onchi, T., McColl, D., Xiao, C., Hirose, A.
Format: Article
Language:English
Subjects:
Central solenoid-less
Coils
Heating
Hysteresis curve
Image field from iron core
Iron
Iron core saturation
Ohmic
Plasma current start-up
Plasma currents
Saturation
Spherical tokamak reactor
Tokamak devices
Transformers
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Summary:•Plasma current can be started up by small iron core without central solenoid.•Iron core removes central solenoid.•Plasma current can be maintained after iron core saturation.•Hysteresis curve shows the partial core saturation.•Image field from iron core is estimated during discharge.•Spherical tokamak reactor without CS is proposed using the small iron core. We propose to use of a small iron core transformer to start up the plasma current in a spherical tokamak (ST) reactor without central solenoid (CS). Taking advantage of the high aspect ratio of the STOR-M iron core tokamak, we have demonstrated that the plasma current up to 10–15kA can be started up using the outer Ohmic heating (OH) coils without CS, and that the plasma current can be maintained further by increasing the outer OH coil current during iron core saturation phase. When the magnetizing current reaches 1.2kA and the iron core becomes saturated, the third capacitor bank connected to the outer OH coils is discharged to maintain the plasma current. The plasma current is slightly increased and maintained for additional 5ms as expected from numerical calculations. Core saturation has been clearly observed on the hysteresis curve. This is the first experimental demonstration of the feasibility of slow transition from the iron core to air core transformer phase without CS. The results implies that a plasma current can be initiated by a small iron core and could be ramped up by additional heating and vertical field after iron core saturation in future STs without CS.
ISSN:0920-3796
1873-7196
DOI:10.1016/j.fusengdes.2014.02.017