Tearing mode induced generation and transport of non-thermal electrons in ADITYA-U tokamak.

Study of runaway electrons (RE’s) with energies in the several keV to tens of MeV is important as its interaction with PFC’s results in large heat loads, sputtering and melting of the vacuum chamber, especially for reactor-scale devices like ITER. To minimize the harmful effects of RE’s on PFC’s, a good understanding of RE generation and transport is required. In tokamak, RE’s are produced during the thermal quench, impurity pellet injection and magnetic reconnection. Amongst these, observation of energetic particle generation due to magnetic reconnection in tokamaks is scarce. In ADITYA-U, Quasi-coherent oscillations are observed in HXR emission from the limiter in synchronous with MHD mode oscillation. The MHD analysis shows, m/n = 4/1 tearing mode is excited with periodic gas puffing and later it transforms to 3/1 tearing mode. With large growth rate of 3/1 tearing mode, MHD modulation starts appearing in HXR emission, C²⁺ spectral line emission and electron density. This work presents a plausible explanation for the experimental observation by invoking non-thermal electron generation due to induced electric field at X-point of 3/1 magnetic island via magnetic reconnection and how this electric field influences transport of these RE’s resulting in the observed periodic burst.