Volume 92, Issue 7, 01 October 2002
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
92(2002); http://dx.doi.org/10.1063/1.1503173View Description Hide Description
The density of electrons formed in binary collisions of neon atoms was measured in the afterglow of a low pressureglow discharge by observing the high energy tail of the electron energy distribution function(EEDF) using a Langmuir probe. In the afterglow, the bulk plasmaelectrons thermalize but the density of neon atoms remains significant. In an ionizing collision, a pair of these atoms releases high energy (∼11.6 eV) electrons which form a characteristic peak in the EEDF. Simultaneously with the chemi-ionization electrons, the densities of and neon atoms were independently measured using diode laser absorption spectroscopy. It was found that the data obtained are described well by a single chemi-ionization reaction when the configuration is considered a single state. The corresponding rate coefficient, found to be at a temperature of 310 K, is recommended for use in discharge modeling.
92(2002); http://dx.doi.org/10.1063/1.1505671View Description Hide Description
The Doppler broadening of ion line profiles emitted by z-pinchplasma provides information about the thermalization of the implosion kinetic energy and the radiation efficiency of the pinch. Measurements of these line profiles are often complicated by source broadening in the instrument and opacity broadening of the emitted radiation. A high resolution concave crystal spectrometer in the Johann geometry was used to record the time averaged spectra of optically thin trace elements in the load. An imaging slit provided radially resolved but axially averaged spectra. The measurements indicate that lower ion temperatures (3–5 keV) are observed for Al wire loads on both the Saturn and Double EAGLE accelerators in the short current pulse mode (60–100 ns) than in the long pulse mode (125–225 ns) where values of 6.3–9.5 keV are observed. These values are smaller than those observed on Saturn by others. Furthermore, the wavelength at the line center of axially resolved ion line profiles on the DM-2 accelerator at Titan was observed to vary about some average value which implies an axially varying fluid motion of the plasma column transverse to the pinch axis.
92(2002); http://dx.doi.org/10.1063/1.1497454View Description Hide Description
Langmuir probe techniques have been used to study time and spatially resolved electron densities and electron temperatures in pulse-modulated hydrogen discharges in two different planar microwave reactors GHz, 1 ms). The reactors are (i) a standing-wave radiative slotted waveguide reactor and (ii) a modified traveling-wave radiative slotted waveguide reactor, which generate relatively large plasmas over areas from about 350 to 500 The plasma properties of these reactor types are of particular interest as they have been used for basic research and for plasma processing; for example, for surface treatment and layer deposition. In the present study the pressures and microwave powers in the reactors were varied between 33 and 55 Pa and 600 and 3600 W, respectively. In regions with high electromagnetic fields, shielded Langmuir probes were used to avoid disturbances of the probe characteristic. Close to the microwave windows of the reactors both the electron density and the electron temperature showed strong inhomogeneities. In the standing-wave reactor the inhomogeneity was found to be spatially modulated by the position of the slots. The maximum value of the electron temperature was about 10 eV, and the electron density varied between 0.2 and The steady-state electron temperature in a discharge pulse was reached within a few tens of microseconds, whereas the electron density needed some hundreds of microseconds to reach a steady state. Depending on the reactor the electron density reached a maximum between 80 and 200 μs after the beginning of the pulse.
Nonlinear transformation of electromagnetic waves in suddenly created cold magnetized plasma: Longitudinal propagation92(2002); http://dx.doi.org/10.1063/1.1505686View Description Hide Description
The transformation of a circularly polarized electromagneticsourcewave in a suddenly created cold magnetized and weakly nonlinear plasma is considered. For the case of longitudinal propagation (a sourcewave propagating along an external static magnetic field) when the ion motion is neglected, a circularly polarized sourcewave splits into four longitudinal oscillating modes. In the case of a linearly polarized sourcewave due to the interaction between its right and left circularly polarized components additional stationary and traveling electron wave modes are created. Amplitude distributions of all created modes are determined in closed form and presented in corresponding diagrams for different values of sourcewave and electron cyclotron frequencies.
92(2002); http://dx.doi.org/10.1063/1.1505991View Description Hide Description
X-ray laser gains and the level populations in collisionally pumped neon (Ne)-like krypton (Kr XXVII) ions have been investigated considering 27 levels of the and configurations in fast moving cylindrical plasma.Effects of opacity of the and transitions on the gain coefficients are considered using escape probability factors in both the static, and dynamic plasmas under the Sobolev approximation, that includes effect of the large velocity gradient. Results indicate that the gain values are significantly affected by plasmaopacity, and the velocity gradient allows us to obtain a broader gain region in dense plasmas.