Speaker
Mr
Jervis Mendonca
(Institute for Plasma Research Gandhinagar INDIA)
Description
The (m=1, n=1) internal kink instability plays an important role in the dynamics of a
tokamak discharge and is responsible for the occurrence of sawtooth oscillations. Many
experimental observations show that plasma rotation can strongly influence the
stability properties of sawtooth oscillations. Past theoretical flow studies to understand such stabilization have been done in the low viscosity regimes. Viscosity can be high in tokamaks due to enhancements from turbulent effects. We investigate the stability of the (1,1) mode in the presence of sheared flows over a range of viscosity regimes using the CUTIE code for both RMHD and two-fluid models. Initially, we use the RMHD version of CUTIE and systematically examine the effects of several kinds of sheared
flows on the (1,1) mode, namely axial, poloidal and combinations of both types of flows
in the linear and the nonlinear regimes. In the absence of flow and for low Prandtl
numbers we observe that the growth rate scalings with resistivity and viscosity agree
with past theoretical results. However, as we increase the viscosity further, the growth
rate scaling changes significantly. It shows that high viscosity can strongly influence the linear growth rate of the modes. We find that in the presence of an axial flow, the
stabilizing influence of viscosity is enhanced and can lead to a complete stabilization of the m = 1 visco-resistive mode at high Prandtl numbers. In the nonlinear regime, for
axial flows, the saturation level of the mode decreases at a higher viscosity compared to the case of no flow but slightly increases at lower viscosity. Similar results are found for the poloidal flow case. In the case of helical flows at high viscosity, there is a significant change in the nonlinear saturation level depending on the flow helicity. We have continued the above studies into the two-fluid regime and found diamagnetic drift stabilization of the (1,1) mode i.e. the growth rate of the (1,1) mode reduces with an increase in the density gradient. The nonlinear evolution of the mode in the presence of imposed shear flows also shows distinct differences from the RMHD results due to the presence of two-fluid effects.
| Country or International Organization | India |
|---|---|
| Paper Number | TH/P5-21 |
Primary author
Dr
Debasis Chandra
(Institute For Plasma Research, INDIA)
Co-authors
Prof.
Abhijit Sen
(Institute for Plasma Research)
Dr
Anantanarayanan Thyagaraja
(Astrophysics Group, University of Bristol, Bristol, BS8 1TL, UK)
Mr
Jervis Mendonca
(Institute for Plasma Research Gandhinagar INDIA)
