Modification of the RELAX for producing tokamaks as well as RFPs for investigating two-fluid toroidal plasmas

The RFP machine "RELAX" has been upgraded to produce tokamak plasmas as well as RFPs to study the validity of two-fluid descriptions for those toroidal plasmas in low density regimes. For this purpose, the strength of the toroidal magnetic field (B_t) in the RELAX was planned to increase up to approximately 0.2 T, which would be about four times larger than that of RFPs. In the case, stronger electromagnetic (EM) forces obviously act on the set of toroidal field coils (TFCs). To mechanically support the TFCs during the tokamak formation, a complete set of three-dimensional EM forces and stresses were calculated by use of a finite element analysis method. According to those results, TFCs were completely fixed and tested in experiments. Regarding the discharge circuit supplying the current flowing into the TFCs, it achieved approximately 21 kA, which corresponds to B_t = 0.2 T. Currently, the first tokamak will be planned in the RELAX. This comparative study would help understanding the two-fluid description of the plasmas with relatively lower density where the ion skin depth is hardly short compared to the plasma size.