Observation of radial propagation of drift waves in the STOR-M tokamak

Summary form only given, as follows. We report experimental observation of radially outward propagation of drift type waves in the edge region of STOR-M tokamak (B = 0.7 T, plasma current 25 kA, average electron density 10/sup 13/cm/sup -3/, q = 3). Density and potential fluctuations were measured with an array of Langmuir probes and propagation nature of fluctuations was analyzed by calculating cross-correlation functions in both poloidal and radial directions. The radial propagation Speed is approximately 8 /spl times/ 10/sup 5/ cm/s when B = 0.7 T. It increases when the magnetic field is lowered in a manner approximately inversely proportional to the magnetic field. Poloidal propagation of fluctuations in the electron diamagnetic direction observed earlier was also confirmed. At B = 0.7 T, the poloidal propagation speed of /spl sim/2 /spl times/ 10/sup 6/ cm/s was seen. The radial propagation speed is thus a large fraction of the poloidal speed Linear theories of the drift ballooning modes in tokamaks do not predict radial propagation. Recent simulation studies have revealed nonlinearly driven radial propagation of fully developed turbulence. Signature of radial propagation has been seen in indirect measurements by Coda et al. In the figure, a typical power spectrum and radial dispersion relation observed at B = 0.7 T are shown. Studies are under way to see if magnetic fluctuations exhibit similar radial propagation.