Study of Ohmic breakdown and burnthrough phase of ADITYA tokamak

Abstract

In the ADITYA tokamak, the plasma discharge is initiated through filament pre-ionization assisted breakdown, using the conventional inductively driven electric field. Following the breakdown of the neutral gas, the discharge is sustained by a successful burnthrough phase. The nature of the breakdown and burnthrough phase is studied by varying the parameters influencing it, such as the toroidal electric field, operating pressure, and lithium wall conditioning. The plasma initiation failures in the breakdown and burnthrough phase are identified, and optimized conditions of operating parameters are derived. The value of the Lloyd parameter Eϕ×BT/Bz in the ADITYA for plasma breakdown is found to be in the range of 1200–2100 V/m, which is consistent with other conventional tokamaks. The applied Ohmic input power must overcome the power losses due to fuel ionization and fuel and impurity radiation to achieve the complete burnthrough. The power requirement for the burnthrough phase is obtained experimentally and compared with the estimated values. The required Ohmic input power is found to be ∼60 kW for the successful burnthrough. Furthermore, it has been observed that the vessel wall coating with lithium reduces the impurities influx in the burnthrough phase and, thus, reduces the Ohmic input power consumption.