[en] Particle confinement time τ_p has been obtained from measurements of poloidal and toroidal distributions of Hα and Lyman α emissions in CHS. These particle confinement times range between 1.5 and 4ms at a constant line-averaged density of 3 x 10¹³cm^-3 for both cases of limiter- and divertor-dominated NBI plasmas with Ti-gettering. In these cases the energy confinement time τ_E were between 2 and 3ms. The density decay characteristic time τ_p^* and global recycling coefficient R have been also measured for Ti-gettered plasmas and large τ_p^* values were observed. As a result high recycling rates (R>0.92) are obtained for a wide density range. For a limiter-dominated case of boronized plasmas (R_ax=92.1cm) values of τ_p were correlated with τ_E and a linear correlation between them was found for normalized τ_E to P^-0.58 which is a power degradation term in LHD empirical scaling. 6 refs., 9 figs

[en] By programming formation of compact toroidal configuration, it was possible to control the losses and spontaneous plasma dynamics during transitional processes. Previously formation modes were studied mainly by the macroscopic parameters. Here trapped flux, magnetic and thermal energy, radial distribution of magnetic field and the other internal parameters have been measured by the combination of internal and external diagnostics. 8 refs., 3 figs

[en] Particle orbit simulations are carried out to study the ion orbits and loss at the edge of a tokamak plasma. The ion loss conditions are examined as a function of υ_PLL/υ₀ and the distance of ion launching points form the magnetic separatrix. The simulation results are compared with the theoretical ones. Good agreements and detailed features are shown in the simulations. 8 refs., 6 figs

[en] Parameter scalings with magnetic field, RF power and filling pressure are presented for RF produced argon plasmas in H-1. Measurements of wavefields excited by the plasma producing antenna are also presented. 5 refs., 4 figs

[en] A spheromak configuration consisting of bias flux surrounding a core region of closed flux surfaces has been successfully sustained in the Flux Amplification Compact Torus (FACT) device by DC/Coaxial helicity injection. In this experiment, the energy transfer efficiency is estimated to be about 30%. The relaxed configuration possesses a low q profile (1/3< q<1/2) whose shape implies that the current density is concentrated in the core and which is maintained by the process of MHD relaxation. The current conversion and rapid inward diffusion of the injected current is found to be significantly related to the n=1 helical deformation of the open field lines along the geometric axis. In this paper, we present some design parameters for the planned Helicity Injected Spherical Torus (HIST) which will permit a corresponding investigation to the above to be made for a tokamak. 5 refs., 4 figs., 1 tab

[en] Here we present the principle of operation of fast algorithm based on the selection of few toroidal harmonics which visibly affect the plasma boundary and discuss the influence of the plasma induced magnetic fields on the shape and sizes of plasma boundary. The existing moderate pressure profile dependence increases as one passes from the shearless system to the system with large shear. Traditional methods for combating plasma induced changes in magnetic configurations by external axisymmetric magnetic fields are analyzed. It is shown that the quadrupole field can not only restore the rotational transform profile but usually visibly destroys external magnetic surfaces. An ill-posed problem of MHD stellarator equilibria identification from the external measurements is investigated and the possibility to restore the plasma profiles in the frame of a two-parametric set of functions using the system of local probes is discussed. In the second part of the work we generalize the well-known method of flux coordinates for the investigation of plasmas with nested magnetic surfaces to compute large-scale magnetic islands. The method for computing structures with several magnetic axes using non-single valued flux coordinates is discussed. 5 refs., 3 figs

[en] The application of radio-frequency (RF) forces to divertor plasma is proposed for the improvement of its relevance to reactors. RF fields are applied at the entrance of closed divertor rooms. Ponderomotive forces sustain high density scrape-off plasma which screens the penetration of neutral atoms into core plasma regions, and create positive electrostatic potential in scrape-off plasma region which suppresses the penetration of impurity ions form divertor rooms. Ponderomotive force for electron is also applied to prevent the upstream flow of cold electrons from divertor rooms to scrape-off regions. Theoretical and numerical studies are summarized. 2 refs., 3 figs

[en] In helical experiment devices, the accuracy of their nonplanar coils affects plasma confinement properties significantly; so coil winding accuracy is one of the crucial issues for their construction. An advanced method for helical coil windings in fusion devices was studied. This new method utilizes a geometrical characteristic of the trajectory of the helical coil, which enables us to improve the accuracy of coils, and is thus expected to improve the mechanical, electromagnetic and super-conducting properties of the coils. This paper presents the new concept of the winding method and practically shows the results of the R ampersand D for the Large Helical Device (LHD). 8 refs., 7 figs

[en] The TS-3 device at the University of Tokyo has been used to produce free boundary spheromaks or spheromak-like compact toroids. Plasma production is accomplished either by Z-Θ discharges or by means of magnetized coaxial plasma guns installed at both ends of the device. The plasmas produced have a minor=major radius of about 15 to 20 cm with a natural decay time of about 30 to 50 μs and a toroidal plasma current of about 30 to 60 kA. A unique feature of TS-3 device is the possession of production regions at both ends of the device, and consequently the ability of producing two adjacent compact toroids which can be merged through magnetic reconnection. Another feature of TS-3 device is the possibility of external application of a toroidal field with the aid of an optional center conductor assembly that can carry an axial current ranging from 0 to ±80 kA. Novel research subjects that have emerged from TS-3 experiments are: (1) the investigation of three dimensional effects of magnetic reconnection in laboratory plasmas, (2) the formation of FRC plasmas by a counter-helicity spheromak merging, (3) non-OH production and merging of tight aspect ratio tokamaks, (4) the stabilization of tilt motions of tight aspect ratio tokamaks, and (5) the formation and compression (flux amplification) of free-boundary tilt stabilized flux-core spheromaks. 18 refs., 10 figs

[en] The prospects of the low-aspect-ratio (A) tokamak to fulfill the requirements of viable fusion power plants are considered relative to the present status in data and modeling. Desirable physics and design features for an attractive Blanket Test Facility and power reactors are estimated for low-A tokamaks based on calculations improved with the latest data from small pioneering experiments. While these experiments have confirmed some of the recent predictions for low-A, they also identify the remaining issues that require verification before reliable projections can be made for these deuterium-tritium applications. The results show that the low-A regime of small size, modest field, and high current offers a path complementary to the standard and high-A tokamaks in developing the full potential of fusion power. 25 refs., 3 figs., 4 tabs