This article discusses recent developments in high-temperature electrostatic levitation technology for containerless processing of metals and alloys. Presented is the first demonstration of an electrostatic levitation technology which can levitate metals and alloys (2-4 mm diam spheres) in vacuum and of superheating-undercooling-recalescence cycles which can be repeated while maintaining good positioning stability. The electrostatic levitator (ESL) has several important advantages over the electromagnetic levitator. Most important is the wide range of sample temperature which can be achieved without affecting levitation. This article also describes the general architecture of the levitator, electrode design, position control hardware and software, sample heating, charging, and preparation methods, and operational procedures. Particular emphasis is given to sample charging by photoelectric and thermionic emission. While this ESL is more oriented toward ground-based operation, an extension to microgravity applications is also addressed briefly. The system performance was demonstrated by showing multiple superheating-undercooling-recalescence cycles in a zirconium sample ( T, = 2 128 K) . This levitator, when fully matured, will be a valuable tool both in Earth-based and space-based laboratories for the study of thermophysical properties of undercooled liquids, nucleation kinetics, the creation of metastable phases, and access to a wide range of materials with novel properties.

Absolute, apparent cross sections for 295-410 nm band emission from naphthalene have been measured over an electron-impact energy range from threshold to 300 eV. Numerous processes, including electron exchange, are observed to contribute to the excitation in the near threshold region. At higher energies direct excitation through optically allowed channels is preferred. The electron-impact-induced fluorescence was found to be unpolarized (<0.5%) in the near-threshold region but showed small negative polarizations of a few per cent at impact energies greater than 25 eV. The radiation decay occurs to excited vibrational levels of the ground electronic state which is expected to lead to strong IR emission.

From accurate spectroscopic constants one finds that the thermal dissociative-attachment process (DA) in DI should be exothermic only for rotational levels J& 8 in U =0. We report herein measurement of an enhancement of DA with rotational temperature T in the range 298 -468 K. The effect is easily accounted for by the increase in total fractional population of excited J levels in DI relative to HI. The effect affords a rotational analog to the use of uibrationally excited molecules (e.g. , HCl) in a plasma to control electron conduction.

The crossed electron-ion beams technique was used to measure absolute cross sections for single ionization of Ar2+, Kr2+ and Xe2+ ions at electron energies ranging from threshold to 2000 eV. The total error in the cross sections at a 90% confidence level is estimated to be +or-4.8, +or-4.9 and +or-7% or less for Ar2+, Kr2+ and Xe2+ respectively, at energies more than a few electron volts above threshold. In contrast to some previous measurements, the metastable contents of the ion beams were small even in the case of Xe2+. All measured cross section curves show significant contributions from excitation-autoionization and possibly direct ionization of inner-shell electrons. There is evidence for resonance-excitation-double-autoionization in the case of Xe2+. Comparisons are made with other available experimental and theoretical data.

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