Edge Biasing of SINP-Tokamak Plasma in High-Q Regime

In high $q$ regime ($q_{edge}=5-7)$ of SINP-TOKAMAK [an iron-core device having major and minor radii of $30$ and \textit{7.5 cm}, respectively and B$_{toroidal}$ = \textit{1.2 Tesla}] fast edge biasing experiment is carried out introducing a Molybdenum electrode of \textit{5mm} in diameter, radially positioned at \textit{7.0 cm}. Biasing seems to cause a change in plasma current density profile forming a negative shear in the region \textit{6.4-6.9 cm} and it leads to better confinement and longer duration of plasma current as was observed\footnote{Ghosh J., Pal R., Chattopadhyay P. K. and Basu D. 2007 Nucl. Fusion \textbf{47} 331} also in very low q (VLQ) regimes of the same machine. The electrode current drawn in this regime is about \textit{5-10 amp}. Lowering of H$_{\alpha}$ signal and loop voltage is also observed indicating better confinement, independently confirmed by diamagnetic loop too. On applying bias, electron density and temperature profile develop sharper gradient near the edge. Interestingly, electrostatic and magnetic fluctuations, observed by inserting electric and magnetic probes in the edge plasma, are suppressed in the inner region (\textit{6.4-6.8 cm}) in the frequency range of \textit{30-70 kHz} by the effect of electrode biasing.