Aufbau und Erprobung eines repetierenden Laser-Blow-Off-Systems zur Untersuchung elektrostatischer Elektronendichtefluktuationen in der Rand- und Abschaelschicht von TEXTOR und Wendelstein 7-AS

High anomalous transport is one of the key problems on the way to a burning plasma. Today it is generally assumed that this anomalous transport is caused by correlated fluctuations of the electric and magnetic fields, as well as of the particle densities and temperatures. The exact mechanisms are not yet, however, completely understood. Hence, the investigation of fluctuations currently has a high priority in fusion research. Therefore, the aim of this work was to determine to which extent Li-beams that are produced by means of laser blow-off (LBO) can be used for the investigation of fluctuations of the electron density in the edge and scrape-off layer of fusion devices and to carry out fluctuation measurements. For this purpose the LBO-system installed on the TEXTOR tokamak has been upgraded for repetitive operation and used for fluctuation measurements on TEXTOR and on the Wendelstein 7-AS stellarator. The principle of this diagnostic is based on the excitation of Li atoms by collisions with electrons of the plasma and the following relaxation into the ground state. This transition into the ground state is accompanied by photon emission. For the total beam, the line emission is proportional the density of both, the Li atoms and the electrons. The penetration depth of the beam is limited by the increasing ionisation of the injected atoms caused by the rise of the electron density towards the plasma center. The spatial resolution in the direction of propagation of atomic beam diagnostics is determined by the velocity of the atoms and the relaxation time of the atomic processes involved. In the case of Li-LBO the spatial resolution is about 2 mm, which is ideal for the investigation of the spatial structure of electron density fluctuations, as these have a characteristic length of 5-15 mm in radial as well as in poloidal direction. Problems arise from the short length of the LBO pulses (ca. 100 #mu#s) and the strong temporal variation of the Li flux, that has to be taken into account during the data evaluation. (orig.)SIGLEAvailable from TIB Hannover: RA 831(3993) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Messung von Elektronentemperatur und -dichte mittels Heliumstrahldiagnostik im Randschichtplasma eines Tokamaks

The helium beam diagnostic is an active spectroscopic method to measure electron temperatures and densities with good spatial and temporal resolution (#DELTA#r #approx# 1mm, #DELTA#t #approx# 1 ms). The method can be applied in the temperature range 10 eV to several hundreds of electron volts, the density range is from 10"1"8m"-"3 to several 10"1"9m"-"3. The method is based on the comparison of measured line intensity ratios with the results of a collisional radiative model. In this work, experimental aspects (e.g. the generation of helium beams) and the methods for the interpretation of the line intensities are investigated. For the optimization of the spatial resolution, an optimized beam source has been developed and put into operation at the Juelich Tokamak TEXTOR-94. The supersonic helium beam has a small beam divergence of #+-#1 and an almost mono-energetic velocity #DELTA#v/v#approx#0.07. The accuracy of the collisional radiative model has been significantly increased using the most accurate atomic data currently available and by regarding all the excited helium states with principal quantum number n#<=#5. Measurements at TEXTOR-94 prove that the accuracy increased significantly. (orig.)92 refs.SIGLEAvailable from TIB Hannover: RA 831(3638) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Barrierenentladungen zur plasmagestuetzten Oberflaechenbehandlung

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Entwicklung eines Finite Elemente Verfahrens zur Modellierung der Plasmastroemung in der Randschicht von TOKAMAKS

The purpose of the work is to to develop a two-dimensional Finite-Element-Code. This code should be able to simulate the plasma flow pattern in the burning chamber of fusion devices by an exact and solution-dependent discretisation. Reionisation and other collision processes of recycled neutral particles are described by coupling the fluid model to the kinetic Monte-Carlo neutral-gas-code EIRENE. For comparison and fundamental numerical studies a fast analytical description of recycling is also available. Such rather crude approximations are employed in other codes often as the only option. It is possible to treat the flow of ions and neutral atoms/molecules near complex surface structures of fusion devices consistently. Because of the time step restriction in the special solution algorithm, up to now the electron temperature profile has to be provided from elsewhere. It can, for example be interpolated from experimental data or from results of other independent code calculations. The newly developed code is applied to a typical TOKAMAK-discharge (TEXTOR) and characteristic results are discussed. (orig./HP)Available from TIB Hannover: RA 831(2942) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

One dimensional model of a tokamak edge plasma under conditions of strong impurity radiation

SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Untersuchung der Eigenschaften einer Argon-Glimmentladung mit Titankathode mittels Langmuir-Sonde und Laser induzierter Fluoreszenz

In this work an abnormal Argon glow discharge with Titanium cathode has been investigated. The results presented are the measurements and calculations concerning the electron beam plasma in the negative glow. Two diagnostics have been employed to determine the plasma parameters. A Langmuir probe has been used in the negative glow to measure the spatial distributions of the electron density, temperature and the plasma potential. Two electron groups were found, slow electrons with a temperature of 0.3 eV and density of #propor to#10"1"1 cm"-"3, and fast electrons with #propor to#3.0 eV and #propor to#10"7 cm"-"3. Under all operational conditions the plasma potential was almost constant within the negative glow and about 1.5 V positive with respect to the anode voltage. The electric field has been calculated from the potential profile. It is shown that, within the error of measurement, this electric field is equal to the ambipolar electric field, which has been calculated from the electron density and temperature profiles. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2655) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Untersuchung der chemischen Reaktionen von energetischem Sauerstoff mit Graphit, B_4C sowie bor- und siliziumhaltigen Kohlenstoffmaterialien

One of the major problems in plasma-wall-interaction is the impurity control of the fusion plasma. In this task the use of carbon as plasma facing material was a major step in reducing the metal and oxygen impurity concentration in the plasma. The remaining impurities were then carbon and oxygen, the last one being responsible for the high carbon contamination of the plasma due to chemical erosion in form of CO and CO_2. It has been found that the use of boron/carbon (B/C) and silicon/carbon (Si/C) materials has significantly reduced the oxygen contamination in the plasma due to a gettering effect and therefore led to an enhanced plasma performance. For a better understanding of the underlying reaction mechanisms irradiation experiments have been performed to investigate the chemical erosion, the retention behaviour, the thermal desorption and the energy distribution of the reaction products during the bombardment of different pure carbon as well as B/C- and Si/C-materials with energetic oxygen ions depending on target temperature. The experiments were performed with a mass separated "1"8O_2"+ ion beam of 2-10 keV in the temperature range between room temperature and 1800 K. The reaction products were detected by means of mass spectroscopy either with residual gas analysis or by direct detection without hitting the wall in a ''line-of-sight'' quadrupol mass spectrometer. The energy of the reaction products was measured by means of ''time-of-flight'' experiments. (orig./MM) overthermal component with a maximum at 0.12 eV whereas the CO_2 molecules are only thermally released. In comparison to pure graphite the B/C- and Si/C-materials have shown an enhanced retention capacity and a reduced chemical erosion yield due to energetic oxygen up to temperatures of 1000 K. The thermal desorption of the retained oxygen occures mainly in form of different boron oxides (BO, BO_2, B_2O_2 and B_2O_3) for temperatures above 1100 K. Besides CO and CO_2 these boron oxides are also released during irradiation of the B/C materials even at room temperature. CO and CO_2 show nearly the same energy distribution as from pure graphite. At room temperature all boron oxides are emitted only with overthermal energies with maxima in the range of 0.06-0.14 eV whereas at higher temperatures and additional thermal component appears. The behaviour of the chemical erosion of the B/C materials is in good agreement with the observed reduction of the oxygen contamination in fusion devices in which such materials are used for plasma facing components. This is mainly due to the high gettering of oxygen and the reduced chemical erosion yield. The appearence of molecules with overthermal energies leads to a higher penetration of the chemical erosion products into the plasma edge and therefore influences the ionization and transport process of those molecules in the plasma. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2995) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Untersuchungen zur physikalischen Zerstaebung an amorphen Kohlenstoffschichten mittels laserinduzierter Fluoreszenz

Available from TIB Hannover: RA831(2647) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Ueber die raeumliche Verteilung der Magnesium-Atome und -Ionen in einer Helium-Glimmentladung mit Magnesium-Kathode Eine Untersuchung mit Laser-induzierter Fluoreszenz

SIGLEAvailable from TIB Hannover: RA 831(2484) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Interaction of pellets with hot plasmas

SIGLEAvailable from TIB Hannover: RA 831(2980) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman