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Fast propagation of sawtooth induced heat pulse is observed in the magnetohydrodynamic (MHD) active plasmas of ADITYA tokamak. The sawtooth crash deposits heat beyond the inversion radius, which gets transported to the edge region of the plasma, and is reflected as inverted sawtooth modulation in the edge channels of electron cyclotron emission (ECE) and ${H_\alpha }$ spectral line emission. The time-lag analysis on ECE signal reveals the propagation time from plasma core to edge of ∼150 µ s. From this analysis, the estimated transient electron heat diffusivity $\chi _{\text{e}}^{{\text{hp}}}$ is found to be ∼50–60 m ^2 s ^−1 , which is ten times higher than that of power balance heat diffusivity $\chi _{\text{e}}^{{\text{pb}}}$ , in the MHD active discharges of ADITYA. It has been observed that the presence of MHD ( m / n = 2/1, 3/1) activity in the intermediate region between the q = 1 and the edge radii, significantly influences the heat transport from the plasma core to the edge region. Stochastic magnetic field region formation with overlapping m / n = 2/1 and 3/1 MHD islands facilitates the fast heat-pulse propagation during a sawtooth crash in ADITYA tokamak. The disparity between the measured and the power-balance estimated diffusivity is significantly reduced by considering the electron heat diffusivity due to stochastization of magnetic field in the intermediate region.

Thermal electron cyclotron emission (ECE) is measured on a medium size Aditya tokamak by a multi-channel Ka-band radiometer and another multi-channel E-band radiometer. The optically thick second harmonic Ka-band radiometer measured signal is affected by the right-hand cutoff effect beyond [?]25 ms. Due to this cutoff, the electron temperature cannot be measured beyond this time. The plasma density is evaluated for the cutoff frequency channel. It is not possible to also determine the electron temperature from the third harmonic optically thin E-band measurements. Yet these measurements are useful to study sawtooth oscillation phenomena. The sawtooth period and amplitude dependence on measurable plasma parameters are determined and new scaling laws are established for Aditya plasma sawtooth. The propagation delays of inverse sawtooth at different radial channels are used to determine thermal diffusivity. The measured diffusivity ( \chi ^{\rm HP}_{\rme}\sim 20{\hbox--}31\,{\rm m}^{2}\,{\rm s}^{-1} ) is found and compared with \chi ^{\rm PB}_{\rme} , which is determined from power balance of background Aditya plasma. The ratio \chi ^{\rm HP}_{\rme}/\chi ^{\rm PB}_{\rme} is 2-3 for the Aditya plasma discharge. This ratio is comparable with a previous study of heat diffusion on medium size tokamaks. [ABSTRACT FROM AUTHOR]