A Design Study of the Power Supply System for Superconducting JT-60
Makoto Matsukawa, Shinichi Ishida, Akira Sakasai, Gen-ichi Kurita, Yushi. M. Miura, Tsunehisa Terakado, Yoshikazu Ohmori, Syunzo Ohmori, Jun Okano, Katsuhiro Shimada, and Nobuyuki Hosogane
Naka Fusion Research Establishment, Japan Atomic Energy Research Institute 801-1 Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 Japan
Abstract.
One of the key issues in steady state tokamak research is how to extend the plasma discharge time. Super-conducting coils and non-inductive plasma current-drive method such as ECCD or NBCD are absolutely necessary. Moreover, continuous or semi-continuous power supplies are required for a super-conducting tokamak. We have studied the possibilities of using existing JT-60 power supplies as those for a super-conducting tokamak.
Since the present power supplies of the JT-60 were designed and constructed originally under an assumption of plasma discharge time of 5 s, one may suppose that a dramatically large scaled modification is necessary to realize a long pulse operation for over 100 s. However, many components of the existing power supply system are still useful because the different types of power supplies are required for super-conducting coils. The voltage rating of the toroidal field coil power supply of a super-conducting machine is very small in comparison with that of the present JT-60, because the excitation time of the super-conducting toroidal field coil is expected to be half an hour or more.
The existing toroidal field coil power supply with 24 diode rectifiers can be modified to that with thyristor converters only by replacing the semiconductor devices. The existing transformers, cables, and VCBs can be reused. The thyristor converters can be rearranged to eight units with ratings of about 600V, 20kA and 300 s. These units can be applied to new poloidal field coils for controlling plasma current ramp-up/down and plasma shaping. However, since these units cannot generate a breakdown electric field, estimated as 0.3 V/m with an assist of ECH, thyristor converter units of the present PFC power supplies will be also inserted in the series connection as booster converters used only in the short period of plasma initiation.
We evaluated the electric power and the energy required for 4 MA plasma operations. As a result, one motor-generator set of 400 MVA / 2.6 GJ (originally used for heating systems) can be used for a high power heating mode of 40 MW / 10 s. While, another motor-generator set of 215 MVA / 4 GJ (originally used for the toroidal field coil power supply) can be applied for a steady heating mode of 10 MW / 100 s.