A magnetospheric configuration gives rise to various peculiar plasma phenomena that pose conundrums to astrophysical studies; at the same time, innovative technologies may draw on the rich physics of magnetospheric plasmas. We have created a "laboratory magnetosphere" with a levitating superconducting ring magnet. Here we show that charged particles (electrons) self-organize a stable vortex, in which particles diffuse inward to steepen the density gradient. The rotating electron cloud is sustained for more than 300 s. Because of its simple geometry and self-organization, this system will have wide applications in confining single- and multispecies charged particles.
Inhomogeneous magnetic field gives rise to interesting properties of plasmas which are degenerate in homogeneous (or zero) magnetic fields. Magnetospheric plasmas, as observed commonly in the Universe, are the most simple, natural realization of strongly inhomogeneous structures created spontaneously in the vicinity of magnetic dipoles. The RT-1 device produces a 'laboratory magnetosphere' by which stable confinement (particle and energy confinement times ∼0.5 s) of high-β (local electron β ∼ 0.7; electron temperature 10 keV) plasma is achieved. By producing a pure-electron plasma, we obtain clear-cut evidence of inward (or up-hill) diffusion of particles. A statistical mechanical model reveals the 'distortion' of phase space, induced by the inhomogeneity of the ambient magnetic field, on which the plasma relaxes into an equilibrium with inhomogeneous density while it maximizes the entropy.
Null points in magnetic fields destroy the adiabatic invariants of charged particle motion, resulting in a chaotic motion. The mixing effect of the chaos produces efficient collisionless heating of electrons. The entropy production is represented by an effective resistance in a macroscopic description. This "chaos-induced resistance" enables plasma production at a low gas pressure suitable for ultrafine plasma etching. [S0031-9007 (98)07155-5] PACS numbers: 52.80.Pi, 05.45. + b, 52.50.Dg, 52.75.Rx
High-β ECH plasma is generated and stably sustained in a magnetospheric configuration, the Ring Trap 1 (RT-1) device, generated by a levitated dipole field magnet. Geomagnetic-field compensation and optimized operation have realized drastic improvements in plasma properties. The maximum local β value has reached 70% and the pressure profiles have a rather steep gradient near the superconducting magnet. Electrons of the high-β plasma typically consist of 70% hot (∼50 keV) and the rest of cold populations. Confinement time of the hot component plasma is 0.5 s with the optimized neutral gas pressure. By removing the coil support structure, the peaked density profile is observed in the strong field region.
The first plasma experiment using the Ring Trap-1 (RT-1) was performed on January 12, 2006. The RT-1 is a novel plasma device constructed to explore ways to the advanced-fuel fusion. The mechanism of plasma confinement is based on the theory of high-beta equilibrium that is self-organized in a flowing plasma. A superconducting ring, levitated in the vacuum chamber, produces a magnetic field that traps high-temperature plasma, creating a magnetosphere-like configuration. Plasma is produced by electron cyclotron heating using an 8.2 GHz microwave.
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