[en] In this thesis plasma diagnostics by emission spectroscopy is reviewed. Considered are He, Ar, H₂, D₂, CH₄, silane, N₂, and O ₂ plasmas. (HSI)

[en] The report is based on an already existing collisional-radiative model for H₂ and H. The underlying model is introduced and the limits of the models are discussed. It is shown that the quality of the results strongly correlates with the quality of the data implied in the model. Possible improvements and extensions of the model are suggested whereas some of the improvements, i.e. changes in transmission probabilities, are carried out and tested. Other suggestions are postponed due to the lack of data to a later time. In a next step, systematic investigations on the equilibrium population of atomic and molecular levels are carried out. Population and depopulation processes are studied and their dependence on electron temperature and electron density is shown. The population of the electronic excited levels of the molecule is connected with molecular ground state, atomic hydrogen and the various hydrogen ions. Therefore, the composition of the ion species in representative laboratory plasmas is calculated by a simplified particle balance. In the case of populations of excited atomic levels the influence of self-absorption of Lyman lines on the emission of Balmer lines is shown. (orig.)

[en] Radio frequency ion sources used in neutral beam injection systems (NBI) of fusion machines are currently supplied by self-excited RF generators. These generators have both a low power efficiency and a limited frequency stability, therefore transistorized amplifiers are being considered for the power supply of the next generation of RF sources. A 75 kW generator, originally designed for broadcasting, has been tested with a negative ion source. High operational reliability and a very good matching to the plasma load has been demonstrated. These results make this generator type a very promising candidate for future NBI systems

[en] Highlights: • NBI is a candidate for a cw tokamak DEMO due to its high current drive efficiency. • The plug-in efficiency must be improved from the present 20–30% to more than 50%. • A suitable candidate is a photo neutralizer with almost 100% neutralization efficiency; basic feasibility studies are underway. • Cw operation with a large availability puts rather high demands on source operation with some safety margins, especially for the components with high power density loads (source back plate and extraction system). • Alternatives to the present use of cesium are under exploitations. - Abstract: The requirements for the heating and current drive systems of a fusion power plant will strongly depend on the DEMO scenario. The paper discusses the R and D needs for a neutral beam injection system — being a candidate due to the highest current drive efficiency — for the most demanding scenario, a steady state tokamak DEMO. Most important issues are the improvement of the wall-plug efficiency from the present ∼25% to the required 50–60% by improving the neutralization efficiency with a laser neutralizer system and the improvement of the reliability of the ion source operation. The demands on and the potential of decreasing the ion source operation pressure, as well as decreasing the amount of co-extracted electrons and backstreaming ions are discussed using the ITER requirements and solutions as basis. A further concern is the necessity of cesium for which either the cesium management must be improved or alternatives to cesium for the production of negative ions have to be identified

[en] Investigations of chemical erosion of carbon (EK98) were carried out in hydrogen and deuterium low pressure discharges. Atomic hydrogen fluxes to the surface were obtained from the radiation of the Balmer lines (Γ_H=Γ_D=2.6 x 10²¹ m^-2 s^-1). From the diffusion flow onto a surface, the reflection coefficients of graphite for H and D atoms were determined to be 40% and 65%, respectively. Erosion yields were derived from weight loss measurements and emission spectroscopy of the CH and C₂ bands at ion energies between 5-40 eV in the substrate temperature range of 300-1100 K. Spectroscopic results indicate the influence of higher hydrocarbons. An isotope effect of 2.5-3 was measured, which vanishes at room temperature and approx. 5 eV ion energy. Here, an erosion yield of 0.1% remains. The measurements were compared with model calculations and were in satisfying agreement. (orig.)

[en] The plasma edge of fusion devices is characterised by cold temperatures with respect to the hot core. Specifically in the divertor region the electron temperature is typically a few eV; in the detached plasma regime where volume recombination dominates it is even below one eV. Here, the survival length of hydrogen molecules produced at surfaces by recombination of hydrogen particles is high. These molecules can undergo a variety of reactions, among them dissociation, dissociative ionization and dissociative recombination. The relevance of these reactions depends on the plasma regime, i.e. whether the plasma is ionizing or recombining or in the transition between both regimes. Another important parameter is the vibrational and rotational excitation in the ground state of the molecule and the ion, which in particular depends on the isotope. Molecules are also important in the negative hydrogen ion sources under development for the neutral beam heating systems for ITER. In the low temperature plasma of these sources the degree of dissociation is less than one and vibrationally excited hydrogen molecules play a dominant role in the plasma chemistry. In particular they are important for the production of negative hydrogen ions in the plasma volume. In these sources, the plasma is separated by a magnetic filter field into an ionizing and a recombining part and dissociative recombination of molecular ions becomes important in the transition region. Close to the extraction system exists an ion-ion plasma (i.e. positive and negative ions are dominant whereas electrons play a minor role) and mutual neutralization with molecular ions is a dominant process. Molecules are also involved in the beam neutralisation and important for beam spectroscopy. Since these sources operate in hydrogen and in deuterium isotope effects are of particular interest. In addition, the presence of molecular species in the plasma may influence the interpretation of diagnostic results. An example is the Balmer line radiation, which is sensitive on dissociative excitation and dissociative recombination and has consequences on the determination of the recycling flux. As a consequence, collisional radiative models need to be used in which the different species are coupled to the excited states of the hydrogen atom: molecules, molecular ions, the atom itself and its ion, and negative ions. The realization however, relies strongly on the availability of the underlying cross sections, which should be taken into account preferably vibrationally – and even more demanding rotationally – resolved. In particular here, the low energy range from the threshold to a few tens of eV is relevant. In contrast, the high energy range of several keV is of interest for beam characterisation. (author)

[en] The determination of molecular hydrogen fluxes in the plasma edge of fusion experiments from molecular radiation requires the precise knowledge of photon efficiencies (S+D)/XB, i.e. the ionization and dissociation processes per emitted photon. Photon efficiencies are calculated by a collisional radiative model for molecular hydrogen which gives dependencies on electron temperature, on electron density and on the vibrational population of the molecule in its ground state. To prove the model, photon efficiencies are measured by gas puffing experiments in the divertor of ASDEX Upgrade at high electron densities (n_e∼10¹⁹ m^-3) and low electron temperatures (T_e∼10 eV). Furthermore, results from laboratory plasmas (n_e∼10¹⁷ m^-3, T_e∼3 eV) are also used for an experimental check of the model. The comparison allows an identification of relevant processes such as dissociative attachment from excited states of hydrogen, thus improving molecular hydrogen diagnostics

[en] Effective rate coefficients for molecular processes in edge plasmas are calculated in a wide parameter range of electron densities and temperatures on the basis of the latest available cross-sections and rate coefficients for the individual reactions. In case of hydrogen molecules and the isotopomeres a vibrationally resolved molecular database with Franck-Condon factors, transition probabilities and radiative lifetimes are generated. An improved collisional radiative model for molecular and atomic hydrogen is introduced and used to calculate effective rate coefficients with and without taking into account vibrational population in the ground state of the molecule. In case of hydrocarbons, a flexible dissociation model is constructed to obtain effective rate coefficients and particle densities for different dissociation chains. (author)

[en] Molecular hydrogen isotopes in the divertor region of fusion experiments may affect the divertor plasma via dissociation, ionization and recombination processes . These processes depend on the vibrational population of the ground state of the molecules. The vibrational populations of D₂ and H₂ were investigated simultaneously at similar divertor plasma conditions, i.e., degree of detachment. The spectroscopic method used, yields vibrational temperatures of 4000-6000 K in the outer divertor, depending on plasma parameters. The isotopes show tendencies, known from laboratory experiments , especially similar vibrational ground state populations up to v=4. As previously shown for pure hydrogen discharges , the interpretation of experimental data and plasma edge simulations (B2-EIRENE) needs a collisional-radiative (CR) model for H₂. With respect to isotope investigations the measurements and parameter studies show that the transfer of the CR model to D₂ needs an implementation of complete data sets, i.e., rate coefficients, or at least reliable scaling of the input data given

[en] Low-pressure silane plasmas (2-20 Pa) diluted with the noble gases helium and argon as well as hydrogen were generated by microwave excitation in order to determine plasma parameters and absolute particle number densities. Specific silane radicals (SiH, Si, H₂, H) were measured by means of optical emission spectroscopy, whereas particle densities of silane, disilane and molecular hydrogen were measured with mass spectroscopy. Experimental results confirm model calculations, which were carried out to determine number densities of all silane radicals and of higher silanes as well as electron temperature. The electron temperature varies from 1.5 to 4 eV depending on pressure and gas mixture. The temperature of heavy particles is 450 K and the electron number density is 9x10¹⁶m^-3. The rotational temperatures of SiH are between room temperature and 2000 K due to increasing dissociative excitation. In the plasma the number density of silane is reduced, whereas the number density of molecular hydrogen is close to the silane density, which is fed in. Particle densities of SiH₃, disilane and atomic hydrogen are in the range of a few per cent of the silane number density. At low pressure the SiH₂ density is similar to SiH₃ and decreases with increasing pressure due to heavy particle collisions with silane producing higher silanes. Particle densities of SiH and Si are only in the range of some 10^-3 of the silane density decreasing with increasing collisions of heavy particles with silane and molecular hydrogen. In mixtures with argon Penning reactions increase the silane dissociation. (author)