ABSTRACT
Conditions for which Rayleigh scattering and redistribution of radiation can be observed are examined. The competition between the relaxation processes and spontaneous emission is shown to determine the conditions for partial redistribution. We investigate specific cases in the singlet and triplet He I atomic system for plasma parameters reachable experimentally in a well diagnosed magnetic multipole source. Partial redistribution on the 2 1S-4 1P at 396.5 nm, 2 1P-5 1D at 438.8 nm, 2 3P-5 3D at 402.6 nm, 2 3P-4 3D at 447.2 nm and 2 3P-4 3S at 471.3 nm fine structure transitions is observed employing a dye laser pumping the He I plasma. We make use of a previously developed two-photon formalism based on the frequency fluctuation model to calculate radiative redistribution functions. Results of the partial redistribution measurements are presented, augmented by a comparison with calculations. This allows us to confirm available electron-atom elastic collision rates to within 20%.
ABSTRACT
Electrical conductivities of nonideal carbon and zinc plasmas have been measured in this paper. The plasma is produced by vaporizing a wire placed in a glass capillary within some hundred nanoseconds. In the case of carbon, vaporization occurs with good reproducibility when utilizing a preheating system. The particle density is in the range of n=(1-10) x 10(21) cm(-3). The plasma temperature, which is obtained by fitting a Planck function to the measured spectrum, is between 7-15 kK. Plasma radius and behavior of the plasma expansion were studied with a streak, a framing or an intensified charge coupled device camera. We compare the measured electrical conductivities with theoretical results, which were obtained solving quantum kinetic equations for the nonideal partially ionized plasmas. In this approach, the transport cross sections are calculated on the level of a T-matrix approximation using effective potentials. The plasma composition is determined from a system of coupled mass action laws with nonideality corrections.
ABSTRACT
Nonideal plasmas of tungsten were produced by vaporizing thin wires of 0.1 mm and 0.3 mm in diameter in small glass capillaries (in air) by means of a short-pulse current from an electrical discharge. For a short period of time, the inner wall of the rigid glass capillary confines the plasma until the induced pressure shock wave disintegrates the capillary. Spectroscopic measurements were carried out on the ejected plasma close to the end of the capillary. The plasma temperature was obtained by fitting a Planck function to the measured continuum spectrum. The resistance was derived from the voltage across the plasma and the current through the plasma. The plasma radius was determined with an intensified charge-coupled device camera and a streak camera and allowed the derivation of the conductivity. Particle densities were of the order of 10(22) particle/cm(3) and electron temperatures were in the range from 10 kK to 22 kK. These measurements are compared with theoretical models and previous work.
