Drift-Alfven waves induced optical emission fluctuations in Aditya tokamak

Abstract

In Aditya tokamak [S. B. Bhatt et al. Indian J. Pure Appl. Phys. 27, 710 (1989)], an increase in the Hα and C2+ intensity fluctuations from the edge region is observed with an increase in the magnetohydrodynamic (MHD) activity. Very small fluctuation amplitudes of Hα and C2+ intensity are observed in discharges where there is no MHD activity compared to the discharges with MHD activity. These fluctuations in the Hα and C2+, measured by optical filter—photomultiplier tube combination—are modulated by Mirnov oscillations having a dominant peak with a common frequency ∼7–10 kHz. Further investigation reveals the presence of strong coherent fluctuations in density and floating potential at same frequency as well. These observations indicate the existence of a nonelectrostatic instability, which may be based on the coupled mode of the drift mode and the Alfven mode. The coherent density fluctuations give rise to the experimentally observed coherent Hα and C2+ intensity fluctuations.