Collective Thomson scattering diagnostic with in situ calibration system for velocity space analysis in large helical device.

A collective Thomson scattering (CTS) diagnostic with a ±3 GHz band around a 77 GHz gyrotron probe beam was developed to measure the velocity distribution of bulk and fast ions in high-temperature plasmas. We propose a new in situ calibration method for a CTS diagnostic system combined with a raytracing code. The method is applied in two situations for electron cyclotron emission in plasmas and in a CTS diagnostic with a modulated probe beam. Experimental results highlight the importance of refraction correction in probe and receive beams. The CTS spectrum is measured with the in situ calibrated CTS receiver and responds to fast ions originating from a tangential neutral beam with an energy of 170 keV and from a perpendicular beam with an energy of 60 keV, both in the large helical device. From a velocity space analysis model, the results elucidate the measured anisotropic CTS spectrum caused by fast ions. The calibration methods and analyses demonstrated here are essential for CTS, millimeter-wave diagnostics, and electron cyclotron heating required under fusion reactor conditions.

Observation of a comb-shaped filamentary plasma array under subcritical condition in 303-GHz millimetre-wave air discharge.

Gas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation. We observed the transition between two types of filamentary plasma arrays in air discharge driven by a 303-GHz millimetre wave. Plasma is ignited at a parabolic mirror's focal point in the overcritical condition. One array parallel to the electric field vector appears with a spacing of λ/4 at the focal point. Filaments then separate into plasma lumps ~10 µs after ignition. At 20 µs, a new comb-shaped array grows in the subcritical condition. Filaments are parallel to the incident beam with spacing of 0.96 λ and elongate towards the incident beam. This comb-shaped array appears only in the electric field plane; bulk plasma with a sharp vertex forms in the magnetic field plane. This array is created by a standing wave structure generated by waves diffracted from the plasma surface. Filamentary plasma array formations can influence the energy absorption by the plasma, which is important for engineering applications such as beamed energy propulsion.

Observation of dynamic interactions between fundamental and second-harmonic modes in a high-power sub-terahertz gyrotron operating in regimes of soft and hard self-excitation.

Dynamic mode interaction between fundamental and second-harmonic modes has been observed in high-power sub-terahertz gyrotrons [T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009); T. Saito et al. Phys. Plasmas 19, 063106 (2012)]. Interaction takes place between a parasitic fundamental or first-harmonic (FH) mode and an operating second-harmonic (SH) mode, as well as among SH modes. In particular, nonlinear excitation of the parasitic FH mode in the hard self-excitation regime with assistance of a SH mode in the soft self-excitation regime was clearly observed. Moreover, both cases of stable two-mode oscillation and oscillation of the FH mode only were observed. These observations and theoretical analyses of the dynamic behavior of the mode interaction verify the nonlinear hard self-excitation of the FH mode.

Generation of a plastic crystal including methane rotator within metal-organic cavity by forcible gas adsorption.

The structural determination of saturated adsorbed methane inside a metal-organic cavity by the forcible pressure swing adsorption method (ca. 13 MPa) through a gas-adsorption equilibrium state gives a methane inclusion crystal even at 298 K. The adsorbed methane molecules regularly locate in the pocket-like narrow corners of the necks of the 1-D channel without disorder. The thermal motion of the pseudo-spherical methane molecules seems to be effectively suppressed in its translation mode but allowed rotation. In cooling to 90 K, the crystal structure remained essentially unchanged while the thermal motion decreased, indicating that a lower temperature reduces the rotation of the adsorbed pseudo-spherical methane. The observed crystal structure could also be influenced by a reduction of the vibrational magnitude, and a phase transition from a static disordered structure to an ordered state might occur. The observed crystal state at a higher temperature should have a plastic crystal nature in terms of the randomness of the orientation of incorporated guests. The single-crystal adsorbent is effective for crystallographic observation of the thermal activated guest forced into regular alignment in the crystal lattice, which can be used as a model of the supercritical fluid.

Selective generation of organic aggregates included within metal-organic micropores through vapor adsorption.

The ethanol vapor adsorption behavior and the inclusion crystal structure of a 1D-transformable coordination polymer host were characterized. The adsorption jump was observed during phase transition or two-phase equilibrium with abnormal adsorption enthalpy caused by the nature of "mass induced phase transition." The included ethanol guests selectively form O-H...O hydrogen bonded pairs inside channels, suggesting selective construction of a specific cluster/aggregate in pores under control of thermodynamic factors and cooperative intermolecular interactions among the guest and channel surface.

A new member of the trombiculid mite family Neotrombicula nagayoi (Acari: Trombiculidae) induces human dermatitis.

We present the first definitive evidence that the mite Neotrombicula nagayoi bites humans under natural conditions in Japan. Initially, bites resulted in mild pruritus without pain. However, skin reactions increased gradually year by year with severe pruritus with pain being reported by the victim after being bitten repeatedly. Six species of trombiculid mites comprising three genera were isolated from soil samples collected from August to October in both 2001 and 2002 at a study site where a man was bitten by N. nagayoi. The dominant species was L. intermedium (72.4%) followed by L. pallidum (8.3%) and N. nagayoi (8.1%). N. nagayoi was found only in August and September. We did not detect the pathogen Orientia tsutsugamushi in any of the unfed larvae, including N. nagayoi, collected from the soil samples.