[en] Short communication

[en] Optical emission spectroscopy was used in the study of the nitriding process of tool steel in DC and RF glow discharges in hydrogen-nitrogen gas mixtures. Main attention was paid to the excited active species in the gas phase, which promoted the nitriding process. The influence of hydrogen concentration in the gas mixture and of the steel surface temperature on the plasma composition and on relative densities of active species in the plasma was investigated and the differences in the reaction degrees in DC and RF discharges are discussed and explained. (J.U.) 1 tab., 5 figs., 9 refs

[en] Recently a new mechanism was proposed by Fisch and Rax which should lead to amplification of lower hybrid (LH) waves at the expense of alpha particle energy, thus improving the LH current drive efficiency. The present contribution investigates the possibility of achieving the conditions on which this mechanism - based on the spatial diffusion of fusion alpha particles - could become operative. The analysis performed shows that in reactor grade tokamaks, the penetration of LH waves into the plasma column is very poor due to the intense electron Landau damping and the complex geometry of the equilibrium magnetic fields. Consequently, at acceptable LHW input power levels, the waves do not reach the regions where fusion alpha power could reasonably compensate the losses of LHW energy due to the damping by electrons. The model of Fisch and Rax is based on special features of the induced diffusion of alpha particles in the energy configuration space. Using suitable Hamiltonian formalism, the LHW-induced radial diffusion of alpha particles and the energy transport between LHW and alpha particles in the frame of generalized quasilinear lines of diffusion constraint, is also investigated. (author) 2 figs., 11 refs

[en] To achieve a better time resolution in measurements of profiles of plasma emission lines by means of an intracavity laser spectroscopy method, a new dye laser pumped by the second harmonic of a Q-switched Nd:YAP laser has been built. The laser part of the apparatus, which consists of a laser generator, amplifier, second harmonic generator and a dye laser, is described in detail, and the results of measurements of the laser output energy (typically 30 mJ/70 ns) are presented. As for the detection part, the diffraction-grating spectrograph tested earlier will be used, in combination with an upgraded digital readout system, the key part of which will be a triggerable CCD camera. (J.U.) 3 figs., 11 refs

[en] Analytic formulas for the electromagnetic field and the energy of a single photon are derived using classical Maxwell electrodynamics. Cylindrical coordinates are used, which express well the rectilinear propagation of light and its corpuscular character. Within the framework of the model described, it is possible to explain all the observed features of photon behavior, and to calculate its energy and the spatial distribution of its electromagnetic field. It is shown that in free space the photon energy is stable within a small volume for an infinite period of time. (J.U.) 8 refs

[en] The Fabry-Perot interferometer was tested for stability in time and linearity, and with respect to its use in plasma diagnostics. The influence of the input diaphragm size and of the input monochromator slit width on the accuracy of interferometric measurements was studied. The tests were performed with the piezoelectrically scanned RC 150 Burleigh interferometer and with a cadmium tube as a testing light source. A high-accuracy computer-controlled A/D measuring system was used. The tests certified that the interferometer is stable within a period of 10 minutes. (J.U.) 9 figs., 8 refs

[en] The low pressure rf plasma jet system is suitable for many technological applications. The Langmuir probe can serve as a simple inexpensive diagnostic tool. A method is presented of solving the most difficult problem with rf discharge probe measurements: how to eliminate the disturbing rf voltage component between the plasma and the probe. Radial variations of probe characteristics measured by a cylindrical probe in a nitrogen rf plasma jet system are also presented. (author) 7 figs., 9 refs

[en] The approximate method of partial characteristics is applied to the prediction of the radiation intensity and of the radiation flux density and its divergence in the sulphur hexafluoride arc plasma. Using precalculated tables of the partial characteristics, it is possible to determine the parameters of the radiative flux for an arbitrary plasma geometry, simply integrating over angles. The method gives an agreement with exact calculations to within 20 per cent, and a considerable reduction of computation time by about four orders of magnitude. (J.U.) 6 figs., 9 refs

[en] A simple and fairly inexpensive new technique for qualitative and quantitative measurements of various gas-phase hydrocarbon species in a flowing gas is reported, and the apparatus for its implementation is described. The method is based on C + N chemiluminescent reactions at low temperatures. Detection of extremely low concentrations of hydrocarbon species was demonstrated. The presence of small admixtures of hydrocarbons in the nitrogen working gas increases the intensity of the CN violet band system at 77 K more than ten times with respect to that recorded at room temperature. The intensities of the CN vibrational band system emitted from the cooled part of the flowing nitrogen afterglow are very specific and can be used as a 'fingerprint' for determining trace concentrations of hydrocarbon species. (J.U.) 2 figs., 5 refs

[en] An enhancement of line average electron density was observed in the CASTOR tokamak when lower-hybrid power was launched into ohmic plasma. A broadening of the density radial profile was also found. Such behavior of density in lower hybrid current drive (LHCD) discharges can be attributed to an improvement of particle confinement. The dependence was investigated of the global particle confinement time on the plasma density and the position in the plasma. A simple model was used to evaluate the total number of particles in the plasma volume. The global particle confinement improved by a factor of 2-2.5 during LHCD. Further improvement of the global particle confinement was found in the plasma closer to the optimum. (author) 5 figs., 5 refs