[en] A simple, accurate, and complete set of approximate formulas is presented for evaluating collisional and radiative transition rates for bound-bound and bound-free transitions in atomic hydrogen. The approximations are chosen in a form which facilitates computer programming and solution of nonequilibrium excitation problems of interest in plasma physics and astrophysics. Detailed comparisons are made with experimental, theoretical, and other semi-empirical results. 30 refs., 8 figs

No abstract available

[en] A scaling law governing the cooling of a finite-length column due to electron thermal conduction loss at the column ends, where the magnetic field lines are intercepted by a cold material wall, is derived. In addition to the electron temperature, both the electron number density and the magnetic field strength are allowed to vary along the field lines. It is shown that the cooling of the column is not very sensitive to moderate spatial variations of number density and magnetic field strength and is well represented by a characteristic cooling time given by tau₀ = 5/2 nL²/K₀, where L is the column half-length and n and K₀ are the number density and coefficient of thermal conductivity at the midplane

[en] Conventional design practice in commercial and laboratory ultrasonic instrumentation results in performance which is less than ideal for many advanced applications in research and in automated systems. The major problems with most such instrumentation can be traced to inadequate dynamic range and to baseline distortion arising from AC coupling between stages. This is a preliminary report on an ultrasonic pulser and receiver/preamplifier system having greatly expanded sensitivity and lower noise characteristics in many ultrasonic applications. In at least one application of the new instruments, an improvement of 30 to 40 dB in dynamic range can be achieved

[en] Interferometric measurements on CO₂-laser-produced plasmas in a 250 kilogauss magnetic field show the development of a slender, well-behaved plasma column with an on-axis minimum suitable for refractive trapping of the laser beam. 3 refs., 4 figs

[en] Space- and time-resolved interferometric measurements of electron density in CO₂-laser produced plasmas in helium or hydrogen are made near the laser focal spot. Immediately after breakdown, a rapidly growing region of approximately uniform plasma density appears at the focal spot. After a few tens of nanoseconds, shock waves are formed, propagating both transverse and parallel to the incident laser beam direction. Behind the transverse propagating shock is an on-axis density minimum, which results in laser-beam self trapping. The shock wave propagating toward the focusing lens effectively shields the interior plasma from the incident beam, because the lower plasma temperature and higher plasma density in the shock allow strong absorption of the incident beam energy. By arranging the laser radiation-plasma interaction to begin at a plasma vacuum interface at the exit of a free-expansion jet, this backward propagating shock wave is eliminated, thus permitting efficient energy deposition in the plasma interior. (auth)

[en] Distortion-free intracavity polarization modulation of an optically pumped CH₃OH laser is shown to be viable. The possible use of this modulation technique to make a multichannel Faraday rotation measurement on a Tokamak device is discussed. In addition, the CdTe Faraday modulator employed in this study is shown to have an anomalously large Verdet constant

[en] Mercury, Hg, is a non-radioactive component in the High Level Waste at the Savannah River Site (SRS). Thus, it is a component of the Defense Waste Processing Facility's (DWPF) process streams. It is present because mercuric nitrate (Hg(NO₃)₂) is used to dissolve spent fuel rods. Since mercury halides are extremely corrosive, especially at elevated temperatures such as those seen in a melter (1150 degrees C), its concentration throughout the process needs to be monitored so that it is at an acceptable level prior to reaching the melter off-gas system. The Hg can be found in condensates and sludge feeds and throughout the process and process lines, i.e., at any sampling point. The different samples types that require Hg determinations in the process streams are: (1) sludges, which may be basic or acidic and may or may not include aromatic organics, (2) slurries, which are sludges with frit and will always contain organics (formate and aromatics), and (3) condensates, from feed prep and melter off-gas locations. The condensates are aqueous and the mercury may exist as a complex mixture of halides, oxides, and metal, with levels between 10 and 100 ppm. The mercury in the sludges and slurries can be Hg⁰, Hg⁺¹, or Hg⁺², with levels between 200 and 3000 ppm, depending upon the location, both time and position, of sampling. For DWPF, both total and soluble Hg concentrations need to be determined. The text below describes how these determinations are being made by the Defense Waste Processing Technology (DWPT) Analytical Laboratory at the Savannah River Site. Both flame atomic absorption (FAA) and cold vapor atomic (CVAA) measurements are discussed. Also, the problems encountered in the steps toward measuring HG in these samples types of condensates and sludges are discussed along with their solutions

[en] The diagnostic instrumentation on TFTR (Tokamak Fusion Test Reactor) and the specific properties of each diagnostic, i.e., number of channels, time resolution, wavelength range, etc., are summarized in tables, grouped according to the plasma parameter measured. For comparison, the equivalent diagnostic capabilities of JET (Joint European Torus) and the Japanese large tokamak, JT-60, as of late 1987 are also listed in the tables. Extensive references are given to publications on each instrument

[en] We report the operation of a high power, narrow linewidth CO₂ laser suitable for application as a pump for pulsed submillimeter lasers. Grating tuning and single mode cw injection have been employed in an unstable ring resonator which produces 100 nsec duration, 200 to 400 Joule pulses on the 9R(22) line with a bandwidth of less than 20 MHz