Survey of fusion reactor technology start-up experiment of the KAERIT

This report describes the results of a study on the hydrogen gas breakdown for plasma initiation in the KAERIT tokamak, which is an iron core device with a major radius of 27 cm and a minor radius of 5 cm. This tokamak is designed to operate in a toroidal field of 4 T, a maximum plasma current of 100 kA, plasma temperature of 1 keV, and plasma density of 5 x 1013 cm-3. At present this device is working in a toroidal field of 0.44 T, a maximum plasma current of 10 kA with pulse duration of 1.8 msec, and a maximum plasma temperature of 39 eV at a plasma density of 1 x 1013 cm-3. The results of the gas breakdown experiments well exhibit the unique characteristics of toroidal discharge. The minimum breakdown voltage is as low as 3 V. It is concluded that the error component of the toroidal magnetic field and the stray fields from the scattered current sources have decisive influence on the discharge initiation. Displacement of the plasma column out of the equilibrium position, due to inadequate control of the equilibrium field, is the most positive cause of the major disruption of the plasma. Theoretical estimation of the temporal evolution of the plasma parameters and interrelation between them by the zero-dimensional calculation model interprets suitably the experimental results at least in the early phase of the current rise stage. This theoretical model can be used to predict the performance of the KAERIT tokamak following upgrade to the design specifications. (Author)