Intrinsic Poloidal Flow Generation and its Role in Sustaining Mean Profiles in a Simple Toroidal Plasma
Event details
| Date | 21.09.2012 |
| Hour | 10:30 › 11:30 |
| Speaker | Dr. T. Shekar Goud, Institute for plasma research, Gandhinagar, Gujarat, India, 382428 |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
In a simple toroidal plasma, it is well known that single particle confinement and hence the equilibrium does not exist. The observed plasma confinement time in the experiments is, however, found to be atleast an order higher than that is theoretically predicted using single particle and E x B drifts. It is understood, therefore, that there must be some mechanism similar to rotational transform in tokamaks. The classical or Bohm diffusion are found to be insufficient to remove the excess charge injected by the filament in BLAAMANN experiments, and hence the cross-field diffusion must be anomalous in nature. More recent observations have lead to understand that the anomalous transport in the poloidal cross-section is connected with coherent structures and blobs. In the present work, the role of fluctuations and intrinsic poloidal flows in sustaining mean profiles in a simple magnetized toroidal plasma has been observed. The experiments have been carried out in BETA, a simple toroidal device at IPR, Gandhinagar, India.
To begin with, the existence of large fluctuations and filling of plasma in the entire radial domain are observed to be associated with each other. Simultaneous measurements on high field side (HFS) and low field side (LFS) have indicated that the onset of fluctuations on LFS is followed by density build up on HFS. In order to understand this correlation more quantitatively, various poloidal flow quantities are obtained. It is observed that the measured average fluctuation driven flow velocity is of the order of mean electric field driven poloidal flow. Interestingly, the fluctuation induced flow is opposite in direction to the mean electric field driven flow, partially accounting for the observed difference between the net flow and the mean electric field driven flow. On increasing the toroidal magnetic field strength, a transition occurs in the nature of fluctuations, from highly coherent at low magnetic field to turbulent at high magnetic field, accompanied by the enhanced poloidal flow and increased densities on HFS. The present work demonstrates that in a toroïdal compressible plasma, the intrinsically generated flows triggered by fluctuations, play a role of "effective rotational transform".
To begin with, the existence of large fluctuations and filling of plasma in the entire radial domain are observed to be associated with each other. Simultaneous measurements on high field side (HFS) and low field side (LFS) have indicated that the onset of fluctuations on LFS is followed by density build up on HFS. In order to understand this correlation more quantitatively, various poloidal flow quantities are obtained. It is observed that the measured average fluctuation driven flow velocity is of the order of mean electric field driven poloidal flow. Interestingly, the fluctuation induced flow is opposite in direction to the mean electric field driven flow, partially accounting for the observed difference between the net flow and the mean electric field driven flow. On increasing the toroidal magnetic field strength, a transition occurs in the nature of fluctuations, from highly coherent at low magnetic field to turbulent at high magnetic field, accompanied by the enhanced poloidal flow and increased densities on HFS. The present work demonstrates that in a toroïdal compressible plasma, the intrinsically generated flows triggered by fluctuations, play a role of "effective rotational transform".
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