Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

186 Biennial Report 2005-07To see the effect of biasing on current profile in high-q regime, various shaped electrodes are beingplanned to be used to produce different radial electric field. In addition, a high rated (200V, 500A)variable inductor is also planned in the bias circuit to modify electrode current rise time and seeits effect. Preliminary results show more pronounced effects compared to those in the very low qregime experiment, however, electrode current drawn is quite low.Debjyoti Basu, Rabindranath PalPP5.2.1.7 Effect of ECR produced pre-ionization plasma in SINP-TOKAMAKThe SINP-TOKAMAK is a small iron-core pulsed type tokamak device. ThO2 coated tungstenfilament is used to produce pre-ionized plasma which is needed for breakdown in plasma discharge.The life time of this type filament is small. Several times it gets damaged and need to be changedduring experiment time. Also, it introduces high Z impurities to severely degrade tokamak discharge.So, an ECR produced pre-ionization is introduced in the machine coupling a 2.45 GHz, 5kwatt magnetron source directly to a radial port through a vacuum window. Successful breakdownof plasma is observed in the device causing reproducible tokamak discharge. The breakdown timedecreased, even lowered the required loop voltage. Now tokamak discharge can be produced evenin smaller toroidal magnetic field (∼1KGauss).Debjyoti Basu, Subir Biswas, Rabindranath PalPP5.2.2 Theoretical Studies in Plasma5.2.2.1 Ion temperature gradient driven mode in presence of transverse velocity-shearin ma gnetized plasmasThe effect of sheared poloidal flow on toroidal branch of ion temperature gradient driven modeof magnetized nonuniform plasma is studied. A novel ‘nonmodal’ calculation is used to analysethe problem. It is shown that the transverse shear flow considerably reduced the growth of theinstability. Small but finite amount of viscosity and/or diffusion enhanced the stabilization process.Nikhil Chakrabarti, Jens Juul Rasmussen, Poul Michelsen†PP5.2.2.2 Nonlinear Hydromagnetic waves in two ion species plasmasA theoretical study has been carried out to see the modification of low-density electron-ion plasmadynamics in presence of heavy third ion species. It is shown that the behavior of such a plasmadiffers from the behavior of a single ion-species plasma. We have solved the stationary state nonlinearequations where the second ion-species is heavier than the first and displayed different plasmaprofiles. Weakly non-linear case is also solved to demonstrate the low amplitude solitons.Manis Chaudhuri, Nikhil Chakrabarti, Rabindranath PalPP