Improved beta (local beta >1) and density in electron cyclotron resonance heating on the RT-1 magnetosphere plasma

Abstract

This study reports the recent progress in improved plasma parameters of the RT-1 device. Increased input power and the optimized polarization of electron cyclotron resonance heating (ECRH) with an 8.2 GHz klystron produced a significant increase in electron beta, which is evaluated with an equilibrium analysis of Grad-Shafranov equation. The peak value of the local electron beta e was found to exceed 1. In the high beta and high-density regime, the density limit was observed for H, D, and He plasmas. The line average density was close to the cut off density for 8.2 GHz ECRH. The density limit exists even at the low beta region. This result indicates the density limit is caused by the cutoff density rather than by the beta limit. From the analysis of interferometer data, the uphill diffusion produces a peaked density profile beyond the cutoff density. The ring trap 1 (RT-1) device is a "laboratory magnetosphere" created by a levitated superconducting ring magnet, which is dedicated to studying physical processes in the vicinity of a magnetic dipole. An inhomogeneous magnetic field creates interesting properties of plasmas that are degenerate in homogeneous (or zero) magnetic fields. The RT-1 experiment has demonstrated the self-organization of a plasma clump with a steep density gradient; a peaked density distribution is spontaneously created through "uphill diffusion" [1-3]. Without direct ion heating, the ions remain cold being virtually decoupled with the hot component (> 10 keV) and low density (< 10 18 m-3) electrons. For the study of two-fluid effects on the plasma flow in a high ion beta plasma, two scenarios are investigated to realize ion heating. Scenario A is an ion heating by an ion cyclotron resonance heating (ICRH). Scenario B is a collision relaxation between electrons and ions. In both cases, achieving the electron density > 10 18 m-3 as a target plasma is essential. The operation regime of the RT-1 device has been investigated and extended to a higher electron density and beta by an increase of the ECRH power up to ~ 50 kW with an 8.2 GHz klystron [4]. The ECRH beams from two launchers L#1 and L#2 were injected with both O-modes. The result is shown as the "conventional operation regime" (gray area) (see Fig. 1). After an upgrade in the ECRH system, the polarizations of millimeter waves from two launchers L#1 and L#2 were changed to optimize the deposition and heating efficiency. A twisted waveguide was inserted in the transmission line to rotate the polarization direction of 90 degrees from O-to X-modes.

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

“…Many wellknown low-frequency instabilities found in other toroidal configurations, e.g., kink, tearing, and ballooning modes, are not found in a dipole plasma torus. Additionally, because the dipole-confined plasma torus can operate with peak plasma beta exceeding unity, 54,55 higher density plasmas would allow the study of high-temperature magnetized plasma turbulence over a wide range of dimensionless scales, spanning astrophysics and fusion science. For example, experiments with a high density, high-beta steady-state plasma torus would allow systematic laboratory study of turbulent transport, including electromagnetic and Alfven wave effects, when both the normalized gyroradius and the normalized ion skin depth are small and comparable, q à $ k à i ( 1.…”

Cyclotron Electromagnetic Instabilities in a Laboratory Dipole Magnetospheric Plasma with bi-Kappa Distributions

“…The dipole confinement concept to simulate a magnetosphere in laboratory conditions was originally proposed by Hasegawa [1]. Presently, there are active experiments on the plasma creation, confinement and heating in devices such as Levitated Dipole eXperiment (LDX) [2,3] and Ring Trap 1 (RT-1) [4][5][6][7]. The RT-1 device is a laboratory dipole magnetosphere (LDM) created by a levitated superconducting ring magnet.…”

“…The RT-1 device is a laboratory dipole magnetosphere (LDM) created by a levitated superconducting ring magnet. In RT-1 plasma is produced and heated by a high frequency wave power (8.2 GHz) in the range of the fundamental electron-cyclotron resonance (ECR) [5]. The first successful results on the ion-cyclotron resonance (ICR) heating with a frequency of a few MHz in RT-1 plasma were reported recently in Ref.…”

Increase in Ion Temperature by Slow Wave Heating in Magnetosphere Plasma Device RT-1

“…A diversity of plasmas is expected to be realized with RT-1. Some of these plasmas such as inward diffusion and selforganized plasmas have been observed [2][3][4][5][6][7]. A dipole magnetic field stably and naturally confines plasma in a high beta state like magnetosphere plasma of planets.…”

“…In the RT-1 device, a high electron beta state has been achieved via electron cyclotron heating (ECH) [5]. The recent power increase and optimization of ECH has made it possible to achieve a local electron beta β e0 > 1 [6]. These high-energy electrons exist in plasmas; their energy was verified to be approximately a few tens of keV from the X-ray spectrum.…”