[en] According to the energy of its particles, plasmas are the fourth state of aggregation of matter after solids, liquids and gases. To change from one to another, it must provide energy and increasing temperature. Increasing temperature significantly in a gas, its atoms or molecules acquire enough energy to ionize to collide, so that at 20,000 K have a lot of gas ionization high. However, atoms and molecules can also by electron impact ionization, absorption photons, chemical or nuclear reactions, or other processes. (Author) 17 refs.

[en] In this report the development of plasma edge diagnostic based on atomic beam techniques fir their application in the CIEMAT fusion devices is described. The characterisation of the beams in laboratory experiments at the CSIC, together with first results in the Torsatron TJ-II are reported. Two types of beam diagnostics have been developed: a thermal (effusive) Li and a supersonic, pulsed He beams. This work has been carried out in collaboration between the institutions mentioned above under partial financial support by EURATOM. (Author) 17 refs

[en] The transients associated with the ignition and the extinction of the cold plasma produced in a low frequency, square-wave modulated, hollow cathode discharge of nitrogen dioxide are characterized by time resolved emission spectroscopy, mass spectrometry and electrical probes. The temporal evolution of the concentrations of neutral species created or destroyed in the NO₂ discharges are compared with the predictions of a simple kinetic model previously developed for discharges of other nitrogen oxides (N₂O and NO). The physical conditions of pressure, gas flow rate, modulation frequency and electrical current in the NO₂ plasma were selected in order to highlight the time-dependent behaviour of some of the stable species formed in the discharge, especially the nitrogen oxide products, whose concentrations show transient maxima. The usefulness of the analysis of the transient results is emphasized as a means to evaluate the relevance of the different elementary processes and as a key to estimate the values of some of the rate constants critical to the modelling. This work is dedicated to the memory of Professor Jose Campos

[en] The transients associated with the ignition and extinction of the cold plasma produced in a low-frequency, square wave modulated, hollow cathode discharge of air are characterized by time resolved mass spectrometry and emission spectroscopy. The time evolution of the concentrations of neutral products measured in the discharge (NO, N₂O, N and O) is compared with the predictions of a simple kinetic model previously developed to characterize low-pressure plasmas of N₂O, NO and NO₂ and a good agreement is found

[en] Energy distributions of ions generated in hollow cathode low pressures dc discharges of different gases and gas mixtures containing Ar, H₂, N₂, O₂ or CH₄ are studied by quadrupole mass spectrometry. The ions are sampled through a small diaphragm in the grounded cathode. The measured distributions are mostly determined by the acceleration of ions in the sheath region between the negative glow and the cathode, displaying in general a narrow peak centred at energies close to the anode potential, but with specific features for the distinct ions. It is shown that information about ion production and sheath collision processes can be derived from the shapes of the different energy distributions. In some cases these distributions are used for the estimation of the relative abundance of ions with the same mass/charge ratio but different compositions in complex gas mixtures.

[en] The destruction of solid glycine under irradiation with 2 keV electrons has been investigated by means of IR spectroscopy. Destruction cross sections, radiolysis yields, and half-life doses were determined for samples at 20, 40, 90, and 300 K. The thickness of the irradiated samples was kept below the estimated penetration depth of the electrons. No significant differences were obtained in the experiments below 90 K, but the destruction cross section at 300 K was larger by a factor of 2. The radiolysis yields and half-life doses are in good accordance with recent MeV proton experiments, which confirms that electrons in the keV range can be used to simulate the effects of cosmic rays if the whole sample is effectively irradiated. In the low temperature experiments, electron irradiation leads to the formation of residues. IR absorptions of these residues are assigned to the presence CO_2, CO, OCN"−, and CN"− and possibly to amide bands I to III. The protection of glycine by water ice is also studied. A water ice film of ∼150 nm is found to provide efficient shielding against the bombardment of 2 keV electrons. The results of this study show also that current Monte Carlo predictions provide a good global description of electron penetration depths. The lifetimes estimated in this work for various environments ranging from the diffuse interstellar medium to the inner solar system, show that the survival of hypothetical primeval glycine from the solar nebula in present solar system bodies is not very likely

[en] Time-resolved emission spectroscopy and quadrupole mass spectrometry are used for the experimental diagnostics of a low pressure (8 Pa) modulated dc hollow cathode discharge of H₂ + 10% N₂. The time-dependent experimental results are reasonably accounted for by a zero-order kinetic model developed in our group and checked previously with steady-state measurements (Carrasco et al 2011 Phys. Chem. Chem. Phys. 13 19561), which is now validated under more stringent conditions. In addition to the discharge precursors, which are partly recycled in wall reactions, NH₃ is produced in small but appreciable amounts. The slower evolution of NH₃, as compared with H₂ and N₂, is traced back to the multistep surface reaction mechanism responsible for its production. An analysis of the time variation of optical emission measurements shows that excited NH(c ¹Π) radicals are essentially formed in the electron-impact dissociation of NH₃. (paper)

No abstract available

[en] The ionic chemistry of various hydrogen mixtures (H₂/N₂, H₂/O₂, and H₂/air) has been studied in low-pressure hollow cathode discharges. The major ions identified in the different discharges (H₃⁺, N₂H⁺, H₃O⁺ and NH₄⁺ ) have been also found in astronomical observations or predicted in astrochemical models. The relative stability of the protonated ions in the various mixtures has been investigated in detail. In discharges of H₂ with small amounts of N₂, O₂ and air, appreciable amounts of NH₃ and H₂O were formed at the reactor walls. The preponderance of the protonated ions in these plasmas was found to be largely dictated by the proton affinity of their respective molecular precursors. Even for small amounts of water and ammonia, proton transfer reactions tend to concentrate the positive charge in H₃O⁺ and, especially, in NH₄⁺ ions. These results support the predictions of some astrochemical models indicating that these ions could be dominant in warm astronomical environments where H₂O and NH₃ molecules evaporate from dust grain mantels. (paper)

[en] The chemistry of low pressure H₂+O₂ discharges with different mixture ratios has been studied in a hollow cathode dc reactor. Neutral and positive ion distributions have been measured by mass spectrometry, and Langmuir probes have been used to provide charge densities and electron temperatures. A simple zero order kinetic model including neutral species and positive and negative ions, which takes into account gas-phase and heterogeneous chemistry, has been used to reproduce the global composition of the plasmas over the whole range of mixtures experimentally studied, and allows for the identification of the main physico-chemical mechanisms that may explain the experimental results. To our knowledge, no combined experimental and modelling studies of the heavy species kinetics of low pressure H₂ + O₂ plasmas including ions has been reported before. As expected, apart from the precursors, H₂O is detected in considerable amounts. The model also predicts appreciable concentrations of H and O atoms and the OH radical. The relevance of the metastable species O(¹D) and O₂(a¹Δ_g) is analysed. Concerning the charged species, positive ion distributions are dominated by H₃O⁺ for a wide range of intermediate mixtures, while H₃⁺ and O₂⁺ are the major ions for the higher and lower H₂/O₂ ratios, respectively. The mixed ions OH⁺, H₂O⁺ and HO₂⁺ are also observed in small amounts. Negative ions are shown to have a limited relevance in the global chemistry; their main contribution is the reduction of the electron density available for electron impact processes. (paper)