Role of fluctuations and flows in sustaining mean profiles in a current less toroidal plasma

Abstract

The flow and fluctuation measurements in a simple magnetized current less toroidal plasma have been conducted. The measured plasma parameter profiles are observed to be accompanied by large fluctuations. The existence of large fluctuations and filling of plasma in the entire radial domain are observed to be closely related to each other. The E×B drift velocities calculated from the gradient of measured mean plasma potential profile have shown significant deviation from the net flow velocity measurements. Interestingly, it is observed that the measured fluctuation driven flow velocity, which is opposite in direction to the mean field driven flow, partially accounts for the observed difference between the net flow and the mean electric field driven flow.

Coherent to turbulence transition, enhanced flow and confinement in a simple toroidal plasma

“…4 The existence of fluctuations, concomitant poloidal flow, and plasma spread in the entire radial domain of BETA has been already demonstrated at low magnetic field ðB T ¼ 220 GÞ. 11 Since the nature of turbulence can vary with B T , the poloidal flow mechanism can be modified resulting in interesting flow dynamics. In the present experiments, the toroidal magnetic field ðB T Þ on the minor axis is set at three different values, viz., 220 G, 440 G, and 660 G and discharge is produced.…”

“…The construction of all the above said probes is described in detail in Ref. 11. At high magnetic field, the ion Larmor radius becomes comparable or less than the dimensions of the Mach probe and hence the measurement technique for the net flow is not applicable.…”

“…This fluctuation driven poloidal flux is found to play a vital role in the generation of self consistent flow and an effective rotational transform. 11 Fluctuation driven poloidal flux is estimated from measurements using a radial array of LPs described in Sec. II and using methodology for analysis described in Ref.…”

“…9 In another set of experiments in BETA, with toroidal field set at one value, characterization of different regions with suitable instabilities has been done. 10 More recently, the role of fluctuations in driving the poloidal flow and achieving an "effective rotational transform" at a fixed magnetic fields has been elucidated, [11][12][13] though a magnetic rotational transform as in tokamaks does not exist in this device. A clear flowfluctuation connection and plasma filling in the entire radial domain has been demonstrated.…”

“…11 The existence of fluctuations in plasma parameters is found to be crucial in generating an effective rotational transform in a current less toroidal device. In continuation of this work, a study of the nature of fluctuations, its transitions with a control parameter such as magnetic field, consequent poloidal flows, and mean profiles in a toroidal compressible plasma are reported in the present work.…”