First plasma experiment on spherical tokamak device utst

The UTST (University of Tokyo Spherical Tokamak) device was constructed for the purpose of exploring the formation of ultra-high beta ST (Spherical Toainak) plasma using the double null plasma merging method. When two plasmas merge together to form a single plasma, magnetic field lines reconnect, and the magnetic field energy is converted to the plasma kinetic energy, increasing the plasma beta. The merging start-up has been demonstrated in the TS-3/4, START and MAST devices using coils inside the vacuum vessel and TS-3 plasma obtained 50% beta. In order to demonstrate the start-up in a more reactor relevant situation, UTST has all poloidal field coils outside the vacuum vessel. The first plasma experiment on the UTST was performed from December, 2007. In the result, the plasma obtained 10kA by using only outer PF coils and single ST was generated at the lower area (z=-0.3 ∼-1.0[m]) close to a washer gun. This result suggests that another washer gun on the top of UTST allows the generation of ST at the upper area and the merging start-up by using outer PF coils.