Inward diffusion driven by low frequency fluctuations in self-organizing magnetospheric plasma

Abstract

The new findings for dynamic process of inward diffusion in the magnetospheric plasma are reported on the RT-1 experiment: (i) The evolution of local density profile in the self-organized process has been analysed by the newly developed tomographic reconstruction applying a deep learning method. (ii) The impact of neutral-gas injection excites low-frequency fluctuations, which continues until the peaked density profile recovers. The fluctuations have magnetic components (suggesting the high-beta effect) which have two different frequencies and propagation directions. The phase velocities are of the order of magnetization drifts, and both the velocities and the intensities increase in proportion to the electron density. The self-regulating mechanism of density profile works most apparently in the naturally made confinement system, magnetosphere, which teaches the basic physics of long-lived structures underlying every stationary confinement scheme.

A generalized Hasegawa–Mima equation in curved magnetic fields

“…For a dipole magnetic field B ∼ 1 T in a trap with size L ∼ 1 m, a roughly constant electron spatial density A e , ℓ = 1, and an electron temperature of 1 keV , one obtains ω ≈ 10 3 Hz. These values are compatible with experimental measurements (see [22]).…”

“…Therefore, it is expected to be useful to characterize drift wave turbulence in systems with strong density gradients and enhanced field curvature and inhomogeneity. In fact, drift wave type turbulence as well as so called entropy modes have been reported in experiments involving plasma confinement in dipole magnetic fields [21,22,23]. These systems typically exhibit a hot electron component, while the ion plasma is cold, suggesting the onset of drift wave dynamics.…”

“…This hypothesis effectively restricts the applicability of the HM equation to plasmas with a small density gradient and to magnetic fields with small curvature or field inhomogeneities. However, experimental observations pertaining to plasmas confined by dipole magnetic fields [16,17] suggest the existence of drift wave turbulence and zonal flows in systems where both the electron spatial density and the magnetic field are characterized by strong gradients over spatial scales comparable to that of electric field and density fluctuations (these low frequency fluctuations are often referred to as entropy modes [18]). In principle, an accurate description of electromagnetic turbulence in such setting could be obtained with the aid of nonlinear gyrokinetic theory [19,20,21].…”

Radially inward particle transport driven by low-frequency instability in cylindrical magnetized plasma

“…Turbulent transport usually consists of competing radially outward and inward components in magnetically confined plasmas [1][2][3][4][5][6][7][8]. For fusion devices, inward transport, i.e.…”

“…turbulent pinch, has various effects. It could help maintain a transport barrier and thus enhance confinement in some cases [1,6,8]. Inward pinch could act as a natural fueling mechanism transporting cold deuterium and tritium (DT) ions near the edge towards the core, and maintaining core DT density profiles [9].…”