Main objective of the LATE (Low Aspect ratio Torus Experiment) device is to demonstrate formation of ST plasmas by electron cyclotron heating (ECH) alone without center solenoid. By injecting a 2.45 GHz microwave pulse up to 30 kW for 4 seconds, a plasma current of 1.2 kA is spontaneously initiated under a weak steady vertical field of B v = 12 Gauss, and then ramped up with slow ramp-up of B v for the equilibrium of the plasma loop and finally reaches 6.3 kA at B v = 70 Gauss. This currents amount 10 percents of the coil currents of 60 kAT for the toroidal field. Magnetic measurements show that an ST equilibrium, having the last closed flux surface with an aspect ratio of R 0 /a 20.4 cm/14.5 cm 1.4, an elongation of κ = 1.5 and q edge = 37, has been produced and maintained for 0.5 s at the final stage of discharge. The plasma center locates near the second harmonic EC resonance layer and the line averaged electron density significantly exceeds the plasma cutoff density, suggesting that the second harmonic EC heating by the mode-converted electron Bernstein waves (EBW) support the plasma. Spontaneous formation of ST equilibria under steady B v fields, where plasma current increases rapidly in the time scale of a few milliseconds, is also effective and a plasma current of 6.8 kA is spontaneously generated and maintained at B v = 85 Gauss by a 5 GHz microwave pulse (130 kW, 60 ms).
By injecting the lower hybrid wave into the microwave discharge plasma at the electron-cyclotron resonance in the WT-2 toroidal device, the toroidal plasma current is generated, started up to /^^ 5 IcA, and sustained by rf power alone, without the Ohmic heating power (rf tokamak). This lower-hybrid-wave-driven current is produced only when high-energy tail electrons, which interact resonantly with the lower hybrid wave, are present in the initial electron-cyclotron resonance plasma.
By injection of microwave power P EC near the electron cyclotron (EC) frequency into an Ohmically heated (OH) plasma in the WT-2 tokamak after OH power is shut off, the plasma current is sustained and ramped up by the EC wave only, without OH power. Here, EC-driven current is generated by EC heating of the suprathermal electron beam in OH plasma. Further, when P EC is injected into plasma sustained by lower-hybrid-(LH-) driven current, the plasma current and its rampup rate increase. Here, EC-driven current is generated by EC heating of the mildly relativistic electrons in LH-driven plasma.
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