Observation of the dissipative trapped electron instability in toroidal geometry

Low frequency plasma density fluctuations have been observed in the common flux volume of the dc octopole. For collision frequencies comparable to the fluctuation frequency (which is close to the diamagnetic drift frequency), the fluctuations are identified as dissipative trapped electron modes. In the high collision frequency range the collisional drift wave is observed. A strong quenching of the trapped electron modes is observed when the local safety factor is a low-order rational number. Very little transport is associated with the observed fluctuations.