Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first-order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a direct abstraction of H atom from H2, and it gives calculated activation energy which is in good agreement with the present experiment.
A supersonic helium beam source operated in pulse mode was constructed for direct measurement of electric field distribution in the tokamak plasma edge region with the aid of laser-induced fluorescence (LIF) technique. In this technique only the polarization has to be observed of a LIF resulting from a laser-excited forbidden transition due to the Stark effect and the electric quadrupole to determine the electric field strength. No calibration is needed of the absolute intensity of LIF and tunable laser used. The helium atom beam density was obtained (about 1020 He atoms cm−2 s−1) at a distance of 7 cm from the pulsed nozzle. A model-type experiment to make clear the influence of a magnetic field on the LIF is reported. Design study was also made to install the supersonic beam and spectroscopic measurement system on a medium size tokamak.
A pressure driven mϭ1/nϭ1 mode is excited by lower hybrid current drive in the WT-3 tokamak ͓T. Maehara et al., Nucl. Fusion 38, 39 ͑1998͔͒. The excitation of the mode is accompanied with the decrease of the magnetic shear and with the peaking of the soft x-ray emissivity profile inside the qϭ1 surface. The crescent-shaped mode structure appeared on the contour map of the soft x-ray emissivity is consistent with that of the quasi-interchange mode. The mϭ1 mode can be suppressed by electron cyclotron heating near the qϭ1 surface. The range of the location of the electron cyclotron resonance layer effective for the complete suppression is much wider and the time scale for the suppression is much faster than those in the case of the suppression of the tearing mode in the ohmic heating plasma.
Ultrahigh purity aluminum with a residual resistivity ratio (RRR) of 60000 65000 was obtained by the ultrahigh vacuum melting method. However, it was necessary to reduce the concentration of the elements with distribution coefficient k>1 to further improve the purity of aluminum. Therefore, we prepared a sample with reduced concentrations of k>1 elements from an ultrahigh purity (99.9999) aluminum material by the zone refining method, and evaluated its purity by electrical resistance measurement and glow discharge mass spectrometry (GDMS). In addition, the zone refining process was simulated, and the distribution of the solute atoms after approximately 10 passes of zone refining was predicted. Moreover, the refining conditions were investigated with the aim of achieving higher purity. In experiments, when the zone width was increased from 60 mm to 80 mm at a zone speed of 60 mm/h, the concentrations of the elements with k>1 in the second half of the material decreased and RRR improved. When the zone speed was decreased to 30 mm/h, a marked effect was observed and RRR increased to about 85000. The distribution of the solute atoms determined from the simulation was in good agreement with the results of GDMS analysis, thus confirming the usefulness of the simulation.
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