Observation of phase pattern accelerating zonal flow

Abstract

We report the first experimental observation of zonal flow (ZF) formation through phase patterning. Here the ‘phase’ refers to the eikonal phase carried by streamer-like mode. It is observed that the phase-gradient profile tends to form ‘shock’ layer structures in regions where there are strong streamer-ZF interactions. The emergence of phase-gradient shock layers invalidate the constant-phase-gradient hypothesis, which is frequently employed in the modulational instability models of ZF generation, and is consistent with a recent theoretical work (Guo et al 2016 Phys. Rev. Lett. 117 125002), which predicts that the phase-curvature (gradient of the phase-gradient) can produce a new Reynolds force and accelerate the ZF. By decomposing the Reynolds’ force of the tilted streamers into a phase curvature driven piece and an amplitude inhomogeneity driven one, it is found that inside the shock layers the phase curvature plays a prominent role in accelerating the ZF. We also explore the formation mechanism of the phase pattern and its consistent dynamics with phase-curvature-driven ZF. These findings potentially open a new way to understand the various elusive self-organization phenomena in plasma turbulence.

Laboratory observation of electron energy distribution near three-dimensional magnetic nulls

“…In order to study the plasma in 3D magnetic null configurations, we constructed the magnetic configuration shown in figure 1(a) on the PPT device [20][21][22]. As illustrated in figure 1(c), a hollow cylindrical permanent magnet is placed on the central axis of the PPT device, with an outer diameter of 152 mm, an 88 mm inner diameter and a length of 140 mm.…”

Experimental observation of the transport induced by ion Bernstein waves near the separatrix of magnetic nulls

“…The PPT device has a cylindrical vacuum chamber with a 250 mm radius and an overall length of 1000 mm. 0-2000 G uniform magnetic field is generated by a pair of Helmholtz coils [11,12]. A dipole magnetic field is constructed by placing a hollow cylinder permanent magnet with an 88 mm inside diameter, a 152 mm outer diameter and 140 mm length on the central axis.…”

Key impact of phase dynamics and diamagnetic drive on Reynolds stress in magnetic fusion plasmas

“…The phase -or tilting -instability is long known to be a possible mechanism to transform convection into sheared flow in ideal fluids [29]. More recently, the phase curvature was identified as the main component of the Reynolds force in a linear magnetized plasma device [38]. Here, we examine the possibility of driving the Reynolds stress solely from such a tilting instability, independently from the actual behavior of the turbulence intensity.…”