H.-J. Kunze

Observation of gain at 18.22 nm in the carbon plasma of a capillary discharge

Abstract Amplified spontaneous emission of the C VI Balmer-α line at 18.22 nm is observed in the plasma of a small, low-energy capillary discharge. Typical gain coefficients are between 1.2 and 2.7 cm −1 , the maximum value observed was about 3.1 cm −1 .

Time evolution of colliding laser produced magnesium plasmas investigated using a pinhole camera

Time resolved studies of colliding laser produced magnesium plasmas are performed using a pinhole camera. A ruby laser pulse is split into two beams using a movable glass wedge and focused onto a planar target or targets placed at 90° to each other. A gated pinhole camera provides an orthogonal view of the collision. Measurements with an aluminum filter allowed identification of soft x-ray production zones. A good interpenetration of the two plasmas was observed in the 90° target geometry, because of higher relative velocities, than in the case of laterally colliding plasmas. The appearance of the collision region depended strongly on the power density and on the separation of the foci on the target surfaces.

Observation of line radiation from highly charged Mo ions in a vacuum-spark plasma

Using a curved-crystal spectrograph of the transmission type the X-ray emission from a low-inductance vacuum-spark with Mo-electrodes has been investigated in the wavelength range 0.5Å<λ}<0.9Å. By means of a noise suppression technique, a number of weak lines have been resolved from the continuum. Comparing the measured wavelengths to results of relativistic energy level calculations these lines are identified as belonging to electronic transitions within singly excited heliumlike MoXLI ions and doubly excited lithiumlike MoXL ions. Continuum and line emission are used to estimate electron temperature and density.

Spectroscopic Investigation of Enhanced Plasma Oscillations in a High‐Voltage Theta Pinch

Intensity and frequency of fluctuating electric fields are obtained from a “plasma satellite” on the 21P ‐ 41D line of helium observed in the piston field of a collisionless shock. In contrast to second‐order perturbation theory only one satellite is seen. The perturbation theory is developed, therefore, to higher orders. Agreement between this theory and experiment is achieved. From the observed level of electric field fluctuations an effective collision frequency of about one‐fourth of the ion plasma frequency can be deduced.

Influence of charge-exchange processes on x-ray spectra in TEXTOR tokamak plasmas: experimental and theoretical investigation

Time-resolved high-resolution soft x-ray spectra from gas-puff injected Ar impurity ions have been investigated for neutral beam heated and ohmically heated discharges in the TEXTOR tokamak. The experimental spectra show systematic deviations from corona model calculations for the line intensities of the forbidden He-like lines x, y, z and the Li- and Be-like dielectronic satellite spectra: theoretical corona model calculations predict intensities significantly too low. High-intensity Li-like inner-shell excited satellites correlate with the neutral beam injection. The discrepancies could also be observed in the stationary phase of an inductively heated discharge. In the heating phase the discrepancies are even larger. We propose charge-exchange processes between the neutral atoms and the impurity ions as an explanation of the experimental findings. Good agreement with the experimental observations can then be obtained without the need for invoking large (anomalous) diffusion coefficients. A self-consistent coupling of the population kinetics of the neutrals and the impurity ions, also taking into account charge-exchange processes from excited states of hydrogen/deuterium permit the determination of the neutral fraction and of the electron lifetime on the sole basis of impurity spectra analysis. Independent Monte Carlo simulations of neutral gas transport also provides the ionization degree in the centre and the electron lifetime. These calculations are also in good agreement with the spectroscopic results.

EUV emission from Kr and Xe capillary discharge plasmas

Kr and Xe plasmas are very intensive emitters in the spectral range of 100-150 A, which is relevant for a number of applications (for example microlithography). We present investigations of the extreme utraviolet (EUV) emission from a slow capillary discharge with Kr and Xe fillings. The emission of Kr ions (Kr VIII to Kr XI) within the range of 70-150 A consists of three bands of lines of about 10 A width with maxima at 116, 103 and 86 A. Xe emission bands of about 15 A width have their maxima at 136 and 115 A (Xe IX to Xe XII). The radiation duration in this spectral range is ~150 ns for both elements. At the optimum conditions, the Kr emission at 103 A is 2-3 times more intense than the Xe emission at 136 A. The measured spectral energy of Kr radiation is about 0.1 J sr-1 A-1. Experimental results are compared with numerical modellings of the dynamics and emission of the capillary discharge plasma, which enables the determination of plasma parameters and the future use of the codes as additional instruments for plasma diagnostics.

Investigation of the diffusion of impurity atoms in plasmas by laser fluorescence

A pulse of aluminum atoms was injected into hydrogen gas and plasma by focusing a TEA CO2‐laser beam onto a solid target. The propagation along the axis of the target was investigated by measuring the local atomic densities using dye laser excited fluorescence. A diffusion model allowed the derivation of diffusion coefficients as well as of the rate coefficient for ionization of the Al atoms from the observations.

Investigation of the He II and He II transitions at high densities

Measurements of Stark profiles of the He II line at and of the He II line at from a well diagnosed plasma of a gas-liner pinch discharge are reported. The plasma parameters were determined independently by Thomson scattering, and we found - , - 7.5 eV when measurements of the He II line were carried out and - , - 5.4 eV for the He II measurements. We compare widths and shifts of the spectral lines with theoretical approximations and present new empirical scalings. While the width of the He II line shows significant discrepancies with lineshape theories, in the case of the He II line profile we find good agreement with some calculations. In particular, to investigate ion dynamic effects we present an accurate measurement of the dip in the centre of the spectral line.

Selective population of the n = 3 level of hydrogen-like carbon in two colliding laser-produced plasmas☆

Abstract The possibility is investigated that charge exchange collisions between ions of a hot plasma (C 6+ ) and a cold plasma (C 2+ ) are responsible for selectively enhanced emission of the C 5+ Balmer-alpha line emitted from the interaction zone of the two colliding laser-produced plasmas.

Time-resolved spectroscopic observations of a high-temperature, high- density plasma in a vacuum spark

The discharge parameters of a low-inductance, high-current vacuum spark were optimized to produce a small “point” plasma with temperatures of 35 keV and densities higher than 1020cm−3. Using two Bragg-crystal spectrometers the time resolved x-ray emission was studied. Lines from helium-like and hyrogen-like ions of the elements titanium, iron, copper, and molybdenum were observed and compared with theoretical predictions. Satellite lines to the Lyman-α transition up to molybdenum are identified as radiative transitions from autoionizing levels of the doubly excited helium-like ionization stages.