End effects of the field-reversed configuration created by a θ-pinch were studied with long solenoidal guide field (GF) attached at both ends of the main θ-pinch coil. It was observed that the onset time of the n = 2 rotational mode (n is the azimuthal mode number) could be delayed with the GF until the endshorting effects propagated back to the main coil. Measurements of the plasma rotation just outside the separatrix showed that the n = 2 mode began to develop when the external plasma was spun up to a certain level in the direction of the ion diamagnetic current. These observations suggest that the n = 2 mode is driven by the endshorting effects.

The transport of energy and particles from a field-reversed configuration (FRC) produced by a theta pinch has been studied experimentally under thejollowing typical plasma parameters in the quasi-static phase: Ti~300eV, T e ~100eV, n e ~ 5 X 10 ls cm~3, < / 3> -1, ~3 and separatrix radius r s ~ 1.8 cm. Energy transport through various processes has been evaluated, consistent with the observed volume-averaged quantities which are changing in time in a quasi-static manner. As a result, it has been found that the dominant energy loss mechanism is particle loss, which accounts for more than 50% of the power flow out of the FRC. The second important process is the electron thermal conduction loss, which is estimated to be roughly 30% of the total loss if impurity radiation losses other than by carbon and oxygen are not important. In contrast, the ion thermal conduction loss is observed to be so small as to be hidden by the experimental errors. Radiation loss has been estimated to play a minor role if the observed (Z e ff> can be ascribed to contaminations of only carbon and oxygen. The inferred energy confinement time r E is 7 /is, which compares with the observed particle confinement time r p of 17 JUS. The data indicate that r p is consistent with classical diffusion theory.

To gain a better understanding of pulsed laser ablation (PLA) processes in high-density fluids, including gases, liquids, and supercritical fluids (SCFs), we have investigated the PLA dynamics in high-density carbon dioxide (CO2) using a time-resolved shadowgraph (SG) observation method. The SG images revealed that the PLA dynamics can be categorized into two domains that are separated by the gas-liquid coexistence curve and the Widom line, which forms a border between the gaslike and liquidlike domains of an SCF. Furthermore, a cavitation bubble observed in liquid CO2 near the critical point exhibited a particular characteristic: the formation of an inner bubble and an outer shell structure. The results indicate that the thermophysical properties of the reaction field generated by PLA can be dynamically tuned by controlling the solvent temperature and pressure, particularly near the critical point.

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The realization of superior reaction fields for the synthesis of nanomaterials with pulsed-laser ablation (PLA) in high-density media, such as liquids, high pressure gases, and supercritical fluids (SCFs), especially near the critical point (CP), and the important role of the formation and evolution of cavitation bubbles for tuning the properties of the nanomaterials have been reported. In this study, to further elucidate the dynamics of the fluid in the stages following PLA, the characteristic behavior of cavitation bubbles formed by PLA plasmas near the CP of CO 2 has been investigated using shadowgraph imaging. The time evolution of the cavitation bubbles can be divided into six phases. These include a double-layer structure and a long-time stagnation of the cavitation bubbles, which are peculiar to experimental conditions near the CP. Both spatial and time scale of the cavitation bubbles are at maximum 4-5 times larger near the CP compared to high-pressure liquid and liquid-like SCF far from the CP.

We propose a cost-effective polychromator with a single interference filter, because interference filters account for large parts of polychromator costs in the conventional Thomson scattering diagnostics with a Nd:YAG laser. Since the interference filters are used to transmit the scattered light in a specific wavelength range, one polychromator tends to have as many interference filters as its spectral channels, which makes high-resolution measurement with a number of polychromators expensive. However, we can save the number of interference filters and thus their costs by reentering reflected light from an interference filter into the same filter at different angles. This is possible, because the larger angle of incidence on the interference filter makes the wavelength of the transmitted light shorter. We measured dependence of transmitted wavelengths on the angles of incidence on one interference filter custom-ordered to transmit 1059 nm and developed the cost-effective polychromator using this dependence. The developed polychromator with a single filter successfully separated three different spectral channels (1043.2, 1051.9, and 1058.4 nm), enabling us to realize the cost-effective Thomson scattering diagnostics.