Density Fluctuation Measurements Using FIR Interferometer on HL-2A Tokamak

Density fluctuations were first measured in the core region of HL-2A tokamak plasma using a newly developed multi-channel FIR interferometer system. In divertor ohmic discharges, we measured the radial density fluctuation levels of 5%, which increase to 10--20% during the appearance of MHD activity. Most of the power density in the density fluctuation spectrum is directly associated with m=2 tearing modes. The fluctuation levels reduce to 1/3 and plasma confinement is improved during off-axis electron-cyclotron-resonance heating (ECRH).