Toroidal Motion Research Articles

Observations on a thermally induced instability between rotating cylinders

The wavy disturbance which is induced by a radial thermal gradient in a Taylor stability apparatus has been studied experimentally. This type of secondary flow occurs at a lower Taylor number than the toroidal vortex motion. It appears that there is no sharp transition associated with the thermally induced disturbance when only the inner cylinder rotates. When the outer cylinder also rotates a necessary condition for the appearance of the wavy motion is that Ω 2 Ω 1 < 1 . The wave form of the wavy motion is similar to that of Tollmien-Schlichting waves observed in a frame moving with the velocity of propagation. The disturbance does not move axially but drifts azimuthally at approximately Ω 1 2 . The wave form is spiral for gradients exceeding about 5°C/cm.

The anomalous diffusion of the current sheath in a toroidal discharge

The diffusion of the current sheath in ZETA is shown to be incompatible with classical resistive diffusion at high rates of energy input or low pressures. In the anomalous region the diffusion time is approximately proportional to mass density and inversely proportional to the applied electric field. There are considerable asymmetries in the toroidal discharge and complicated convective motions during the diffusion phase, but these appear not to be the primary cause of the enhanced diffusion. Evidence has been obtained that the enhanced diffusion is not due to the presence of a probe in the plasma. It is therefore probable that there must be an enhanced resistivity, depending on the local values of mass density and electric field, which is presumably due to some form of turbulence, but none of the simple models of such turbulence considered account for the results.