Edge plasma fluctuations in STOR-M

Summary form only given. In the STOR-M tokamak, the coherence and propagation character of the density and magnetic fluctuations are investigated both in the scrape-off layer and at the plasma edge. It is found that the electromagnetic mode is dominant in the main discharge. The propagation direction of fluctuations is in the electron diamagnetic direction. Around f/spl sime/250 kHz, the poloidal wavenumber, k/sub /spl delta=2.0 cm/sup -2/ is of the order of the reverse electron skin depth. These observations support the skin size electromagnetic drift mode, which predicts that a low-/spl beta/ tokamak discharge is unstable against the skin size electromagnetic instability with a phase velocity significantly smaller than the electron diamagnetic drift velocity.