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Stabilization of resistive wall modes (RWMs) is one of the important issues in magnetic fusion research. In the reversed field pinch (RFP), the number of unstable RWMs becomes smaller by lowering the aspect ratio (A), the ratio of the minor to major radius of the device. In REversed field pinch of Low‐Aspect ratio eXperiment (RELAX), whose aspect ratio is 2, unstable m/n = 1/2 RWM was stabilized by a single mode control power supply system with improvements of discharge performance. In this paper we report new results with modified power supply system in which magnetic boundary condition near the poloidal gaps is controlled. The modified power supply system is designed to stabilize the most unstable m/n = 1/2 mode by use of the saddle coil array covering the whole torus with eight (8) power supplies. The results show that the discharge duration is improved from ~ 3.0 ms to ~ 4.0 ms, limited by the capability of the iron core in RELAX device. Stabilization of the dominant RWM with the resultant improved plasma performance by a single mode control power supply system shows one of the advantages of a low‐aspect‐ratio RFP concepts. [ABSTRACT FROM AUTHOR]

Stabilization of resistive wall modes (RWMs) is one of the important issues in magnetic fusion research. In the reversed field pinch (RFP), the number of unstable RWMs becomes smaller by lowering the aspect ratio (A), the ratio of the minor to major radius of the device. In REversed field pinch of Low‐Aspect ratio eXperiment (RELAX), whose aspect ratio is 2, unstable m/n = 1/2 RWM was stabilized by a single mode control power supply system with improvements of discharge performance. In this paper we report new results with modified power supply system in which magnetic boundary condition near the poloidal gaps is controlled. The modified power supply system is designed to stabilize the most unstable m/n = 1/2 mode by use of the saddle coil array covering the whole torus with eight (8) power supplies. The results show that the discharge duration is improved from ~ 3.0 ms to ~ 4.0 ms, limited by the capability of the iron core in RELAX device. Stabilization of the dominant RWM with the resultant improved plasma performance by a single mode control power supply system shows one of the advantages of a low‐aspect‐ratio RFP concepts. [ABSTRACT FROM AUTHOR]

Levitation of pollen particles has been demonstrated in a radio frequency (RF) plasma. Pollen particles from Japanese cypress are levitated to various heights from lower electrode, where they spontaneously form quasi ordered state. Levitating pollen particles are identified from divinylbenzene particles in real-time using the polarization imaging technique. [ABSTRACT FROM AUTHOR]

A crystallike structure was successfully formed as a result of the levitation of a kind of bacillus microorganisms $Klebsiella ~pneumoniae$ in a radio frequency (RF) plasma. The crystallike structure was confirmed to be hexagonal from top-view photograph. Neutral gas friction cools the particles down to equilibrium positions. Field Emission Scanning Electron Microscope (FE-SEM) measurement suggests that RF plasma processes the surface of levitating microorganisms. [ABSTRACT FROM AUTHOR]

This paper reports the levitation of micro-organisms in the sheath of radio-frequency (RF) plasma. Based on simple force-balance calculations, the required electric field for the levitation of micro-organisms has been estimated. It is predicted that micro-organisms could levitate at the periphery of the sheath. Experimental results demonstrate the levitation of two species of bacillus micro-organisms Escherichia coli (E. coli) and Klebsiella pneumoniae in an RF plasma. The almost monodiverse Klebsiella pneumoniae levitating in the RF plasma formed an ordered state similar to a 2-D Coulomb crystal. Diverse E. coli particles demonstrate the tendency that the levitating height of micro-organisms decreases as the radius of particles increases. Levitating micro-organisms in plasmas can be referred as dusty plasmas. [ABSTRACT FROM AUTHOR]

This study analyzes the feasibility of a new method for monitoring the three-dimensional (3D) shape of an asymmetrically magnetized high-temperature toroidal plasma. The proposed method utilizes multiple pinholes on a single disk. Devoid of any assumptions on the plasma shape, 3D tomography images of T e and n e can be successfully created using mathematical methods based on an expansion of the Fourier–Bessel series and a regression analysis on the dataset of the multiple soft X-ray filaments in numerical experiments. [ABSTRACT FROM AUTHOR]

The initial result of 3-D reconstruction of dusty plasma obtained through the integral photography technique has been reported. Integral photography has been applied to observe fine particles floating in a horizontally parallel-plate radio-frequency plasma. By using a simple system with a lens array and a standard charge-coupled device camera, we can identify the 3-D position of dust particles from a single exposure image obtained from one viewing port. [ABSTRACT FROM PUBLISHER]

In the formation of vortical crystal structures of electrons, the distribution of background electrons works as a “cooler” of randomly moving, intense vortices. We examine the supporting effect of background electrons to forming crystal structures from the perspective of a reduction of the vortices’ random motion. [ABSTRACT FROM AUTHOR]

A hot helical structure in low-aspect-ratio (A) reversed field pinch (RFP) is obtained with the soft X-ray (SXR) imaging technique. Tangential SXR imaging camera and high-speed camera system is applied to low-A RFP for studying quasi-single-helicity RFP state. The helical structure correlated with m = 1/n = 4 tearing mode is identified by means of a subtraction technique. [ABSTRACT FROM AUTHOR]

Beyond single-fluid magnetohydrodynamics, multi-scale plasmas have been widely employed in recent studies on toroidal plasmas. To comparatively investigate two-fluid plasmas in a single machine, we devised an efficient method for designing an optimal set for comprehensively supporting existing toroidal field coils (TFCs) linked to a torus chamber. Electromagnetic forces acting on the TFCs and the strain in the TFCs were precisely calculated by using a three-dimensional (3D) finite element analysis method. Based on the obtained results, various additional support components to be attached to specific weak places of the TFCs were determined. Experimental studies revealed that the strain observed in the TFCs was reduced to considerably less than its yield strain by using the additional support components. The value of the strain was consistent with those of 3D simulations. The aid of additional support components to existing TFCs allows modern comparative studies such as those on two-fluid plasmas in the same machine, in which tokamak edges as well as reversed-field pinches with low densities and distinct safety factors are considered. The results can provide insight into the two-fluid plasma mechanism, thus aiding future fusion plasma development. • An efficient method was developed for designing a minimum set for supporting existing toroidal field coils (TFCs). • Forces as well as the strain in the TFCs are calculated by using a three-dimensional finite element analysis method and consistent with measurements. • Obtained results can provide guidelines for the development of additional support components for TFCs of any other existing toroidal machines. • Comparative studies between circular cross-section tokamaks and RFPs in the same machine with relatively low density will promote our understandings for two-fluid toroidal plasmas. [ABSTRACT FROM AUTHOR]

We developed a new Mie-scattering ellipsometry system for the analysis of the generation and transport of dusts in large plasma devices, such as nuclear fusion experiment devices. The system is a rotating-compensator type and consists of polarizer and analyzer modules and a 2-D image sensor. A preliminary experiment was carried out using a small dust plasma cubic chamber. Spherical divinylbenzene polymer particles of 2.25~\pm ~0.05~\mu \textm in diameter with a dispersion degree of 0.1 \mu \textm were injected and suspended in an argon plasma. Light intensity data for 1600 pixels on each image taken 30 times per second were summed as a function of compensator azimuth angle, and then, ellipsometric parameters $\Psi $ and $\Delta $ were determined through Fourier analysis and relational equations. By the comparison of the determined $\Psi $ and $\Delta $ values with the calculated ones based on the Mie theory, it can be stated that they agree fairly well with each other and the measurement method is reliable. [ABSTRACT FROM AUTHOR]