Hot cathode preionization for tokamaks

Preionization of a tokamak discharge was performed in the CCT device with an emissive LaB₆ cathode and has been compared to initiation of discharges with a 15 kHz breakdown oscillator. The cathode produced plasmas with densities locally of up to 1.4×10¹⁹ m^-3, a factor of 100 denser than oscillator-produced plasmas, and five times more dense than the ohmic discharges in CCT. UV emissions indicate that the cathode plasma is concentrated in the top 20 cm of the vacuum vessel, while oscillator discharges and the main tokamak discharges occupy a much larger percentage of the vessel