Magnetohydrodynamic Instability Modulated Runaway Electron Losses in the ADITYA-U Tokamak

In ADITYA-U tokamak, modulation in Hard X-ray (HXR) emission from the limiter synchronous with a m/n = 2/1 tearing mode is observed during the flat-top and pre-disruption phases of a discharge. The oscillation in the HXR signal is observed for a minimum magnitude of poloidal magnetic field perturbation , induced by a m/n = 2/1 magnetic island. Moreover, m/n = 2/1 tearing mode harmonics are pronouncedly visible in the HXR signal. The measured HXR energy spectrum in the absence of 2/1 tearing modes shows high counting statistics of HXR photons in the energy range 1 - 3 MeV, in contrast, in presence of a 2/1 tearing mode, relatively low counting statistics of HXR photons are recorded in the same energy range. The modulation of the HXR signal in the presence of the m/n = 2/1 magnetic island is explained by a periodic RE loss due to resonance between the RE drift orbit and the m/n = 2/1 radial magnetic field perturbation.