Topological bifurcation of helical flows in magnetized plasmas with density gradient and parallel flow shear

Abstract

The topological bifurcation of the flow in non-equilibrium magnetized plasmas is demonstrated by a turbulence simulation. A system with two generic sources of turbulence, the gradients of density and parallel flow, is considered. Topological index of the flow is introduced, in order to indicate the chirality of flow pattern. We here report that the turbulence-driven flow forms the structure of co-axial helixes with opposite chirality. By changing the source of plasma particles, which modifies the density gradient, the transition between three turbulent states is obtained. In addition to the two turbulent states, which are dominated by the drift wave and the D'Angelo mode, respectively, the new state is found. In this third state, fluctuations are driven by both of the free energy sources simultaneously, and compete with the others. The result illustrates the generic feature of turbulence flow generation in non-equilibrium magnetized plasmas.

Ion temperature measurement by laser‐induced fluorescence spectroscopy in panta

“…The assumption of T i / T e ∼0.1 in the previous experimental studies (such as the resistive drift wave and D'Angelo mode ) were verified. These assumptions in nonlinear simulations were also confirmed. Our experimental result provides valuable information for the evaluation of nonlinear processes of the plasma turbulence.…”

“…Despite this, in our turbulence experiment for linear magnetized plasma at Kyushu university (LMD, LMD‐U and PANTA), we have assumed that T i / T e ∼0.1 , where T i is the ion temperature, and T e is the electron temperature. Our simulation studies in linear magnetized plasma also assume that the ion temperature is much lower than the electron temperature and neglect the effects of ion temperature . Therefore, it is strongly required to measure the absolute value of the ion temperature and to validate the assumption experimentally.…”

“…The effect of Zeeman splitting is evaluated for a more accurate assessment of the ion temperature measurement by changing the direction of the polarization axis on a linearly polarized laser beam. In PANTA, many nonlinear turbulence phenomena have been identified . The accurate measurement of ion temperature allows us to more precisely compare observed fundamental processes of turbulence with models.…”

Turbulence Simulation on Zonal Flow Formations in the Presence of Parallel Flows

“…The circular cross-section of plasma with a uniform axial magnetic field is considered. The model equation is based on the three-field reduced fluid equations [25],…”

“…Although the axial phase propagation is symmetry (the magnitudes of the modes with the positive and negative phase velocity are the same) without the parallel flow, the finite parallel flow violates this symmetry and the preferential phase propagation direction appears. This asymmetry in the axial propagation leads to the generation of the parallel momentum flux, which works to suppress the parallel flow shear [25]. At the same time, the fluctuation drives the zonal flow as seen in the bottom center of Fig the azimuthal and axial mode numbers, respectively.…”