Parameter Comparison of TST-M and TST-2
TF & OH coil system
Toroidal Field 0.2-0.3T
Ohmic Volt Second 25mVs
Plasma Parameters
Major Radius ～0.38m
Minor Radius～0.28m
Aspect ratio >1.3
Elongation 1.0 -1.5
Plasma Current < 60kA (<150kA transiently)
Discharge Duration < 10ms
TF & OH coil system
Toroidal Field 0.2-0.4T
Ohmic Volt Second 130mVs( 260mVs)
Plasma Parameters
Major Radius ～0.37m
Minor Radius～0.23m
Aspect ratio 1.6
Elongation 1.2 -1.8 ( < 2.5)
Plasma Current 200kA (400kA)
Discharge Duration 50ms (100ms)

TST-2 (Tokyo Spherical Tokamak - 2) has been constructed as an upgrade of the TST-M (Tokyo Spherical Tokamak - Modified) device. On TST-M, experiments on helicity injection and turbulence-induced transport have been carried out with plasmas of relatively short pulse length (several milliseconds) and low plasma current (60 kA). On TST-2, the maximum flux capability of the ohmic coil will increase from 25mVs to 130 mVs and the toroidal field will increase from 0.3T to 0.4T. These changes will extend the plasma current capability to about 0.2 MA and the discharge duration to about 50 ms, enhancing the quality of discharge flat-top for transport studies. However, the aspect ratio will be restricted to a moderate value of 1.6 or higher. In addition to continuing the research program of TST-M, radio frequency (RF) experiments are planned.

TST-2 has a newly manufactured vacuum vessel that is continuous in the toroidal direction. The vacuum vessel consists of a 1.4 m diameter, 6 mm thick stainless steel cylinder and top and bottom domes. The height of the vacuum vessel is 1.5 m. The inner wall of the vacuum vessel is made of a 0.23 m outer diameter, 1.6 mm thick Inconel-625 tube. The new center stack consists of a 239-turn, double-layer ohmic solenoid and the center legs of the 24-turn toroidal field coil. The ohmic coil is designed to provide a flux swing of 260 mVsec in the double-swing mode. Four pairs of poloidal field coils are used for compensating the ohmic leakage flux, production of the equilibrium field, and creation of the poloidal field null during the breakdown phase. The first plasma is scheduled in the summer of 1999.