Turbulence Dynamics with the Coupling of Density Gradient and Parallel Velocity Gradient in the Edge Plasmas

Abstract

Theory of parallel shear flow driven instability (PSFI) and its impact on turbulence dynamics and transport are presented. The mode is linearly unstable when the parallel flow shear exceeds a critical value. The quasilinear particle flux contains both outward and inward components. Nonlinear dynamics is formulated in terms of hydrodynamic helicity balance. The result implies that once excited, PSFI with helicity may spread from the excited region to stable regions. Implication for turbulence in scrape off layer plasmas is discussed.

The ecology of flows and drift wave turbulence in CSDX: A model

“…The PSFI describes turbulence production due to free energy released from parallel flow shear. 22,23 In contrast to other linear plasmas, 24,25 experimental results from the CSDX linear device show that the parallel flow shear v 0 z is well below the critical threshold necessary to drive PSFI. 21 The PSFI is thus heavily damped in CSDX, and will also not be considered here.…”

“…22,25,30,38 Theoretical studies also show that both axial and zonal flows are driven by turbulence, particularly by the non-diffusive residual stress in both expressions for hṽ xṽy i and hṽ xṽz i. 21,23,32,39,40 Reference 26 investigates the relation between the axial and azimuthal flows and turbulence, and formulates a new zonal momentum balance theorem for the coupled drift-ion acoustic waves. Due to acoustic coupling, a dynamical mechanism for ZF generation is established.…”

Implication of Parallel Velocity Gradient-Driven Instability with Hydrodynamic Electrons to SOL Width

“…With the aim to describe transport phenomena in the SOL region in fusion plasmas, we use the extended Hasegawa-Wakatani equation with parallel flow [17][18][19]25]. As previously proposed, to demonstrate the fluctuation that we focus on, this model is represented as a simplified fluid description.…”

“…These flows lead to a radial gradient, which can drive instability, hereafter called as parallel velocity gradient (PVG) instability [15]. Lately, PVG has been studied theoretically [16][17][18][19], experimentally [20,21] and using simulations [22,23]. In [18,21], it is reported that PVG contributes to inward particle pinch, which can be disadvantageous for SOL broadening.…”

“…Lately, PVG has been studied theoretically [16][17][18][19], experimentally [20,21] and using simulations [22,23]. In [18,21], it is reported that PVG contributes to inward particle pinch, which can be disadvantageous for SOL broadening. However, PVG may change its transport feature in the future devices, such as in ITER.…”