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.

A new high-β and high-density state is reported for a plasma confined in a laboratory magnetosphere. In order to expand the parameter regime of an electron cyclotron resonance heating (ECH) experiment, the 8.2 GHz microwave power of the Ring Trap 1 (RT-1) device has been upgraded with the installation of a new waveguide system. The rated input power launched from a klystron was increased from 25 to 50 kW, which enabled the more stable formation of a hot-electron high-β plasma. The diamagnetic signal (the averaged value of four magnetic loops signals) of a plasma reached 5.2 mWb. According to a two-dimensional Grad-Shafranov analysis, the corresponding local β value is close to 100 %.

The self-organization of magnetospheric plasma is brought about by inward diffusion of magnetized particles. Not only creating a density gradient toward the center of a dipole magnetic field, the inward diffusion also accelerates particles and provides a planetary radiation belt with high energy particles. Here, we report the first experimental observation of a 'laboratory radiation belt' created in the Ring Trap 1 (RT-1) device. By spectroscopic measurement, we found an appreciable anisotropy in the ion temperature, proving the betatron acceleration mechanism which heats particles in the perpendicular direction with respect to the magnetic field when particles move inward. The energy balance model including the heating mechanism explains the observed ion temperature profile.

We have developed an ion cyclotron resonance of frequencies (ICRF) heating system for the Ring Trap 1 magnetospheric device. We excite slow waves from the polar region of the dipole magnetic field. The target helium plasma is produced by electron cyclotron heating. The electrons comprise high-temperature (>10 keV) and low-temperature (<100 eV) components with both typically exhibiting the densities of same order of magnitude. The ICRF heating causes an increase in the ion temperatures and toroidal flow velocities in the core plasma region.We observe appreciable temperature differences between the different ion species (main He + and impurity C 2+ ), suggesting a strong influence of the charge-exchange loss due to which the bulk ions remain relatively cold (~20 eV) compared to the impurity ions (~40 eV). By EX/P3-47 2 developing an electro-optical measurement system, we have measured the local wave electric field in the plasma.

Ion cyclotron range of frequencies (ICRF) heating with a frequency of a few MHz and an input power of 10 kW was applied for the first time, to the best of our knowledge, in a magnetosphere plasma device. An antenna was installed near the pole of a dipole field for slow-wave excitation. Further, a ∩-shaped antenna was implemented and characterized for efficient ion heating. Electron cyclotron heating with an input power of 8 kW sustained helium plasmas with a fill gas pressure of 3 mPa. ICRF heating was then superimposed onto the target plasma (H, D, and He). While the ICRF power was turned on, the increase in ion temperatures was observed for low-pressure helium plasmas. However, the temperature increase was not clearly observed for hydrogen and deuterium plasmas. We discuss the experimental results in terms of power absorption based on result calculated with the TASK/WF2 code.