抄録
The tokamak with the aspect ratio less than 2 is called spherical tokamak (ST), since the plasma is naturally elongated and has a spherical shape. It is being theoretically and experimentally shown that ST has a high potential to confine the very high beta plasma (beta=plasma pressure/magnetic pressure). The blanket module can be easily replaced in ST. If the internal transport barrier and the high bootstrap current fraction are established in ST, the economical fusion reactor would be more realistic.
