In the ELMO bumpy torus, neoclassical transport coefficients depend critically on the ambipolar electric field. These coefficients, calculated for arbitrary radial electric fields, are applied in a one-dimensional radial-transport calculation which, for the first time, treats the electric field self-consistently. This purely classical model predicts many features of experimental operation including a steady-state solutions with radially inward-pointing ambipolar fields.

Nonlinear coupling of four Langmuir waves is studied as a new saturation mechanism for parametric instabilities in underdense plasmas with approximately equal electron and ion temperatures. When treated in conjunction with the usual ion nonlinear Landau damping, these processes produce a saturated Langmuir-wave spectrum with a single peak and a saturated wave energy linearly proportional to the pump intensity. These results are in good agreement with laboratory experiments.

Ruby-laser Thomson scattering have been used to measure ion density fluctuations in a C${\mathrm{O}}_2$-laser-heated gas-target plasma. Nonthermal enhancements of > ${10}^4$ have been observed for $k{\lambda }_{\mathrm{D}}\sim 0.5$ implying $\frac{\delta n}{n}>0.1\mathrm{}$. Ion fluctuations of this magnitude may be giving rise to enhanced absorption of laser radiation in the plasma.

Plasma was generated by focusing a 35-psec, 1.06-μm laser onto Perspex. Ion expansion characteristics were measured relative to laser polarization and incidence angle. Thermal and "fast" ions were always seen. For optimum resonance absorption conditions the thermal ion energy increased, and a second faster-ion group appeared. Comparison with a computer code showed that the faster ions originated from electron accerleration by an intense electrostatic field.

Highly absorbing silica-based glasses exhibit a distinct minimum in the temperature dependence of the very-far-infrared absorption coefficient near 10 K. The associated anomalous absorption at lower temperature can be understood by the two-level tunneling model. Different amorphous materials manifest a considerable diversity in the anomalous behavior.

Using a pulsed superconducting-quantum-interference-device (SQUID) NMR technique, relaxation of the longitudinal magnetization in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been measured in magnetic fields of 31, 102, 180, and 306 Oe in the pressure range 16-26 bar. It is observed that in both superfluid phases there is a temperature-dependent, well-defined spin-tipping angle, ${\theta }_c$, for which the relaxation of the magnetization changes from an exponential to a nonexponential behavior.

Scattering of thermal He atoms from a low-temperature graphite (0001) surface was carried out. The measured diffraction pattern shows that the repulsive part of the periodic gas-surface potential is rather well represented by the first Fourier component. The "hard wall" peak-to-peak spatial modulation is 0.21 Å. Bound-state resonances allow one to determine four distinct energy levels of the laterally averaged potential well. A comparison with available adsorption data is presented.

Fine structure consisting of more than twenty sharp lines has been observed near the absorption edge of silver-doped ZnTe single crystals containing dislocation loops. Possible explanations for the observed spectrum based on excitons bound to the dislocation loops or on "dangling bonds" associated with the presence of the dislocation loops are advanced. This is the first indication of a possible connection between absorption spectra of crystals and the dislocation loops contained therein.

We determine the exchange splitting in ferromagnetic Ni by means of angle-resolved photoemission from a (111) surface. The optical selection rules arising from use of the ($1\overline{1}0$) mirror plane of detection are used to identify the contributions from the majority- and minority-spin sub-bands. The splitting at the top of the $d$ bands turns out to be about 0.5 eV at the point $(0.14, -0.43, -0.43)\frac{2\pi }{a}$, in good agreement with a recent self-consistent band-structure calculation by Wang and Callaway based on the exchange potential of von Barth and Hedin.

Recoil-free $\gamma$ rays from the decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ are frequency modulated by vibrating the source with a piezoelectric crystal and one of the lines of the resulting multiplet emission spectrum is absorbed. The remaining radiation displays a time-dependent counting rate whose harmonic composition and relative phases are sensitive to small energy shifts and can be used for their measurement.

The well-known results of the coherent-potential-approximation (CPA) alloy theory are useful for understanding the energy-gap variation in semiconductor alloys. A CPA theory of the valence bands in III-V compounds demonstrates that alloy disorder can contribute significantly to the band-gap bowing parameter, while causing very little broadening of the $E_0$ spectra. We conclude that the CPA should replace the earlier theories for studying the electronic structure in semiconductor alloys.

Arguments are given that the spin-glass problem has lower critical dimensionalities (below which no transition takes place) of 3 for vector spin-glasses and ≥ 2 for Ising spin-glasses. Thus for vector spin-glasses, the physical case is also at lower critical dimensionality, which is relevant to the peculiar behavior observed in classical spin-glass alloys.

We present experimental evidence of a unique, ordered chemisorption phase in the initial interaction of oxygen with the Al(111) surface. At high oxygen exposure or high temperature, this phase is shown to transform irreversibly to a bulklike aluminum oxide. The measured temperature dependence, as well as the low-energy electron diffraction, suggests a threefold, centered bonding site. A comparison between calculated and experimental valence-band density of states for the oxygen-covered Al(111) surface is made for the estimated oxygen-atom-substrate-surface distance.

A method of stably trapping, cooling, and manipulating atoms on a continuous-wave basis is proposed using resonance radiation pressure forces. Use of highly focused laser beams and atomic beam injection should give a very deep trap for confining single atoms or gases at temperatures ∼ ${10}^{-6\mathrm{}}$ °K. An analysis of the saturation properties of radiation pressure forces is given.

We use the renormalization-group method of Kosterlitz to study the dynamics of a purely relaxational model for the roughening transition. Implications of our results for the behavior of spatial and temporal correlation functions of a crystal-vapor interface and for the crystal growth rate are discussed.

The vacuum decay rate of orthopositronium formed in a gas is determined, after extrapolation to zero gas density, to be 7.056±0.007 μ${\sec }^{-1\mathrm{}}$. The discovery of two systematic effects in a previous powder experiment is discussed. A new measurement of the decay rate in Si${\mathrm{O}}_2$ powders yields results in agreement with the new gas value. The experimental values are still in disagreement with the most recent theoretical calculation, 7.0386±0.000 16 μ${\sec }^{-1\mathrm{}}$.

Using the Stanford Linear Accelerator Center Hybrid Facility 1-m bubble chamber with tantalum plates, a search was made for single electrons or positrons produced directly in 18-GeV/c ${\pi }^{\pm }$ interactions. At 90% confidence level (C.L.), $R=\frac{e^{\pm }}{{\pi }^{\pm }}<2.4\mathrm{}\times {10}^{-5\mathrm{}}$. In addition, a limit can be set on charmed particle pair or associated production channels in terms of their semielectronic decay branching ratios, namely, $\sigma [R_1+R_2]<\mathrm{}2.4\mathrm{}$ μb at 90% C.L.

We suggest that the crossing of the ground rotational band by a second rotational-aligned band may in fact be a double crossing. From extrapolations of the rotational energy formula, we show that one could expect such a second crossing around $I\approx 30$ in ${}_{}{}^{158}{}_{}{}^{}\mathrm{Er}$. This provides an alternative explanation in terms of a double band crossing for the second discontinuity recently observed in the moment of inertia about $I=28\mathrm{}$ in ${}_{}{}^{158}{}_{}{}^{}\mathrm{Er}$.

The spin-dependent capture cross section ${{\sigma }_{+}}^c-{{\sigma }_{-}}^c$ of slow neutrons ($\lambda =1.074\mathrm{}$ Å) by ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ has been determined from the flipping ratio of a transmitted polarized neutron beam as a function of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ polarization. We used two methods, one of which also enabled us to measure the spin-dependent scattering length $b_{+}-b_{-}$ of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. We find ${{\sigma }_{+}}^c-{{\sigma }_{-}}^c=-1170\mathrm{}\pm 50$ b and $b_{+}-b_{-}=(-0.38\mathrm{}\pm 0.05)\times {10}^{-12\mathrm{}}$ cm.

$\gamma$- ray multiplicities $〈M_{\gamma }〉$ and energies $〈E_{\gamma }〉$ associated with identified products of completely damped collisions of 237-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ with ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ are analyzed to determine the angular momenta of the primary heavy fragments. Extending the analysis to the system 175-MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$+Ag allows a comparison which indicates that different partial waves contribute in these two nearly identical composite systems at almost the same excitation energy and that the transition from fusion-evaporation to deep-inelastic reactions occurs over a wide range of partial waves.