Forecasting of disruption in ADITYA-U Tokamak

The first indigenously built ADITYA tokamak has been upgraded to ADITYA-U tokamak (R0 = 75 cm, a =25 cm), having feasibility of having shaped plasma operation with divertor coils. In ADITYA-U tokamak plasma breakdown is generated using hydrogen gas as a fuel and toroidal electric field produced with central solenoid Ohmic transformer coils. Toroidal magnetic field along with some other magnetic field is used to confine the plasma. Disruptions in tokamak, is a sudden loss of magnetic confinement of plasma. A huge amount of plasma current abruptly terminates in a few milli-seconds. Therefore, a huge amount of induced electric field is generated, which makes the electron highly energetic (Runaway electrons) and eddy current flows through the vessel. Hence, due to disruption there is a chance of severe damage to the system. Avoidance of disruption and real time mitigation is a very important field of work in tokamak. There are many possible causes for disruption. The most important reason is growth of m=2 mode of instability. Growing instability at q=2 rational surface gives the major disruption. It is observed that higher q-value (q=6) at the edge gives the sharp falling of plasma current. Where the fall of plasma current is slower for lower q-value (q=3) at the edge. The amplitude of oscillation of m=2 mode also decreases with higher q-value at the edge and increases with lower q-value at the edge. The work is focused on finding a strong correlation between qedge and disruptions in ADITYA-U tokamak. Details of the study will be presented. (author)