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Some recent advancements in the development of powerful high frequency gyrotrons that generate coherent radiation in the sub-terahertz and terahertz regions of the electromagnetic spectrum as well as their typical and novel applications are presented and discussed.

The analytical formulation of the neoclassical resonant diffusion is derived in order to investigate the ion radial transport in the non-axisymmetric mirror cell of the GAMMA10 tandem mirror, where GAMMA10 contains non-axisymmetric mirror cells for flute/interchange stability. The non-axisymmetric mirror, however, causes the neoclassical transport of ions. The remarkable point of the analysis is that the ( ψ , θ ¯ , l ) coordinates are adopted in the derivation of the analytical expression. Especially one coordinate l is taken along the drift orbit of resonant ions trapped in a magnetic mirror cell, by which the drift equation is able to be bounce-averaged along the 0th order ion orbit trapped in a non-axisymmetric mirror cell even in the case of large ion azimuthal drifts.

A novel inclusion crystal, {[Rh(II) 2 (bza) 4 (pyz)] n · 3 n (N 2 O)} ( 1 ), was prepared and characterized by single-crystal X-ray diffraction analysis; linear alignment (N 2 O) n coherently generates in the channels of host rhodium benzoate pyrazine and there is a high possibility of the existence of an intermediate phase induced by a slight amount of adsorbed N 2 O inside the crystal even at room temperature.

A novel porous solid of ruthenium(II, III) dimer complex, [Ru2(p-O2CC6H4NHCOtBu)4Cl], constructed by intermolecularly linking the hydrogen bonds of NH ⋯ O and NH ⋯ Cl was synthesized and the porous structure was crystallographically determined. The dried crystalline solid shows a high BET surface area determined by measuring the adsorption of nitrogen gas and water vapor.

Results of edge plasma investigation in a minimum-B region of the GAMMA 10 tandem mirror are described. In this experiment, the spatial profile of the ion saturation current and the floating potential in the edge plasmas are measured by using arrays of Langmuir probes installed on conducting plates in anchor cells together with a movable probe near the plate in the east anchor cell. From these measurements, a significant asymmetry to the axis of the plasma was observed in both probe currents and floating potentials. It is also found that there are some impurity-deposited layers partially observed on all the conducting plates and that their locations show a rotational symmetry to the magnetic axis at 180°. In this region, a strong gradient of the magnetic field strength toward the axis exists. The direction of the expected plasma shift corresponds to the ∇ → B and curvature drift for ions. The results of ion orbit calculation taking account of the above effect show a good agreement with the measured results.

In GAMMA 10, the radiation pattern of a heating wave of fundamental ECRH for potential formation was not axi-symmetric but vertically elongated on the resonance surface. The non-axisymmetric radiation pattern caused a non-axisymmetric potential profile and likely induced a radial loss. Then, the radiation pattern has been axi-symmetrized. Accordingly, an almost axi-symmetric potential profile has been obtained and a large density increase during ECRH has been observed in the central cell. This implies that radial losses associated with ECRH have been substantially reduced. A new antenna has recently been installed for additional plug electron heating (second ECRH). With this antenna, a larger power and/or a longer pulse width have become available. In a most recent experiment, we have succeeded in axial plugging with a duration up to 0.15 s by sequential use of the usual ECRH and the second ECRH. Moreover, there is an indication that the second ECRH is more desirable for further reduction of the radial loss.

A crystalline solid, [Rh(II)2(bza)4(1,5-nptd)]n (bza and 1,5-nptd=benzoate and 1,5-naphthyridine), was synthesized and characterized by single-crystal X-ray diffraction analysis; the microporous compound demonstrates gas adsorbency with a N2 BET surface area of 291.6 m2 g−1.

A novel gas inclusion solid was generated by cooling an empty host crystal of copper(II) benzoate–pyrazine in a carbon dioxide environment and characterized by single-crystal X-ray diffraction analysis.

This paper studies modifications of convective heat transport in terms of electric and magnetic forces acting on electrons streaming along open field lines. The heat transport is greatly affected by the potential profile along the field lines. One important mechanism of the transport is associated with the exchange of impingig warm electrons with cold electrons produced near or on the surface of plasma-facing walls such as end plates and divertor plates. A recently developed potential model predicts that the end plate potential deepens associated with reduction of cold electron emission. In the GAMMA 10 tandem mirror a negatively biased mesh placed in front of the end plate has successfully suppressed secondary electron emission and leads to deepening of the end plate potential. In the thermal dike ECRH works to mirror reflect colder electrons back to the plate by increasing their pitch angles. The consequent potential depression enhances reflection of warm electrons reaching the plate.

Two aspects of ECRH experiments in the GAMMA 10 tandem mirror are described. One is hot electron production in a minimum- B anchor cell by second harmonic ECRH. When a resonance region is located at the centre of the anchor cell, hot electrons are piled up near the centre region and the β-value attains more than 20%. For off-centre resonance, hot electrons have a spatial profile like a baseball seam. This profile is explained by a drift orbit of an electron in a minimum- B field. The other topic is observation of an intense axial electron flow with energy from hundreds of eV to a few keV generated by fundamental ECRH in the end cells. The force due to the fundamental ECRH driving heated electrons into the mirror loss cone is particularly strong. A bounce averaged Fokker-Planck code with a quasi-linear diffusion operator reproduces the electron flow with the same energies. The electron flow is a predominant ingredient for generation of the electrostatic potential in the GAMMA 10.

A novel crystalline solid, [Cu(II)2(O2CPh)4(2,5-dmpyz)]n (2,5-dmpyz = 2,5-dimethyl-pyrazine), was synthesized and characterized by single-crystal X-ray diffraction analysis. The compound demonstrates multistep phase transition induced by CO2 adsorption, which readily obeys the Clausius–Clapeyron equation in terms of the set of partial pressures of CO2 and transition temperatures.

We report on resistivity and susceptibility measurements of the superconducting Nb 1− x Ta x Se 3 single crystals with 0.14≤ x ≤0.16. Its crystal structure is the same as that of NbSe 3 and the highest T c is 6 K at x = 0.15. The measurements of the upper critical field H c2 revealed the quasi two-dimensional nature and the angular dependence of H c2 is consistent with the anisotropic effective mass model.

GAMMA 10 experiments have shown strong end plugging when sloshing ions and ECRH coexist in one of plug/barrier end cells. This plugging has been achieved with the plasma density in the central cell much higher than that of the plug/barrier region and the barrier density lower than the plug density. The electron temperature in the plug is about three times that of the central cell. These results are consistent with the formation of a thermal barrier in the axisymmetric end cell. The confining potential of 300 ± 100 V is produced in a plasma with nec ∼- 2× 1012/cm3, Tec− 50 eV and Tic ∼- 100 eV.