A large-amplitude backscatter instability, consistent with Brillouin, occurs when a prepulse plasma is formed ahead of a high-irradiance (${10}^{15}$-${10}^{16}$ W/${\mathrm{cm}}^2$) Nd-laser pulse. These results indicate that temporally structured laser pulses suggested for laser pellet implosion may also encounter large backscatter.

Substantial electron heating by energetic-neutral-beam injection has been observed in Oak Ridge tokamak (ORMAK) plasmas. Impurity radiation is enhanced by injection but only to the degree expected for Ohmically heated discharges with the same total power input to electrons, and the electron heat conduction loss is comparable with that in Ohmically heated plasmas. The scaling of average electron temperature with total power input to electrons is approximately the same with or without injection.

Double-layer thin films of high-$Z$ metal and low-$Z$ polyethylene and each single-layer film were irradiated with a 1.06-μm, 200-psec laser pulse at intensities from ${10}^{14}$ to 7 × ${10}^{14}$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$. From the measurements of the transmittance of the laser through these films, the spatial distributions of the transmitted light, expanding ion currents, and x rays, the energy transport is found to be due not only to superthermal electrons but also to x-ray radiation in a high-$Z$ material.

Doublet plasmas have been produced in Doublet IIA using an active field-shaping coil system. Significant increases in the electron density and energy confinement time have been observed for the doublet configuration relative to elliptic and circular plasmas in Doublet IIA.

The mobility of positive and negative ions has been studied as a function of temperature, electric drift field, and (in the $A$ phase) magnetic-field direction in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$; the $A$-phase mobility is observed to be anisotropic with ${\mu }_{\perp }>{\mu }_{\parallel }$ for both positive and negative ions.

The critical behavior of a three-dimensional antiferromagnet described by a six-dimensional order parameter has been investigated by the Monte Carlo technique. A first-order phase transition is observed. This result is in agreement with the prediction of renormalization-group calculations in $4-\epsilon$ dimensions and with neutron scattering experiments on U${\mathrm{O}}_2$, but in contrast to the mean-field theory, which leads to a second-order phase transition.

The induced-torque experiments of Holroyd and Datars show evidence for an anomalous anisotropy in the residual resistance of potassium of about five to one. We show that this is consistent with the hypothesis that the conduction electrons are in a static charge-density-wave state. The importance of torque and de Haas-van Alphen experiments on the same specimen is emphasized.

A new model, based on an extremely strong coupling between the electronic and vibrational systems of certain defect centers, is proposed to explain the phenomenon of persistent photoconductivity observed in some compound semiconductors. The model is supported by data on donor-related defects in $n$-type ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ which exhibit the features characteristic of this effect: a very large Stokes shift (thermal depth, ∼0.1 eV; optical depth, ∼1.2 eV); and a very small (<${10}^{-30\mathrm{}}$ ${\mathrm{cm}}^2$), thermally activated, electron-capture cross section at temperatures below 77 K.

Photoelectron spectroscopy using synchrotron radiation has been used to study the electronic structure of single-phase stoichiometric Th${\mathrm{H}}_2$ and ${\mathrm{Th}}_4$${\mathrm{H}}_{15}$. Th-derived conduction bands are observed together with lower-lying hybridized bonding bands. For ${\mathrm{Th}}_4$${\mathrm{H}}_{15}$, a narrow $d$-like conduction band (∼0.6-eV full width at half-maximum) separated from other bands by a 2-eV band gap is seen. Energy-dependent cross-section measurements for the various bands have been used to determine hybridization and angular momentum character.

We report the first systematic measurements of the temperature dependence of excess noise in metals. The magnitude of the noise in thin films of both Cu and Ag shows a rapid increase with increasing temperature between 90 and 350 K. In Ag, the noise reaches a maximum at $T_p\cong 410$ K, then decreases slowly. In Cu, the peak occurs at $T_p\cong 490$ K. The strong observed temperature dependences is in sharp disagreement with the predictions of current models for the origin of the noise.

Phonon transport in $\beta$-Sn crystals was studied by heat-pulse techniques using superconducting tunnel-junction detectors. The temperature-dependent attenuation by the quasiparticles was measured at fixed frequency (≃ 160 GHz), while, at lower temperature (0.6 K), the ballistic transmission was monitored up to the onset of pair-breaking frequencies. A new method of determining the energy gap follows, which is shown to apply to nonequilibrium states of the bulk.

Magnetization measurements on single crystals and powders of ${\mathrm{Hg}}_{2.86}$As${\mathrm{F}}_6$ show flux expulsion when samples are cooled in a small magnetic field, indicating superconductivity below 4.1 K. The observation of anisotropic flux expulsion with magnitude dependent upon the orientation of the external field with respect to the crystalline axes confirms the anisotropic superconductivity first observed in conductivity measurements.

We present the first experimental study of $n=1\mathrm{}$ exciton-polariton fluorescence in a semi-conductor under resonant optical excitation. An order of magnitude enhancement of the radiative efficiency, a substantial narrowing of the fluorescence linewidth, and highly nonthermal energy distributions are observed at resonance. These new effects are interpreted in the polariton framework, stressing the dependence of polariton lifetime, damping, and escape time on energy and distance from crystal surface.

Inelastic neutron scattering experiments have been performed on binuclear ${\mathrm{Cr}}^{3+}$ clusters and trinuclear ${\mathrm{Fe}}^{3+}$ clusters embedded in molecular complexes. The intensities of transitions within the exchange-split ground state observed at various transfers exhibit an oscillatory behavior due to interference effects which are a direct picture of the metal-metal distances in the cluster. From these measurements, precise magnetic-form-factor data of ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Fe}}^{3+}$ have been obtained.

Potential differences have been measured between a normal probe and a superconducting probe attached to a superconductor held in a temperature gradient. These observations suggest that a thermoelectrically generated quasiparticle current is flowing in the superconductor and allow evaluation of the thermal transport coefficient for the quasiparticles.

Localized orbital calculations are presented for the electronic structure of Chevrelphase molybdenum chalcogenides. Densities of states at the Fermi energy, $N\left(E_{\mathrm{F}}\right)$, are found to depend sensitively on the modification of intercluster interactions because of lattice distortions introduced by the ternary component. Calculated $N\left(E_{\mathrm{F}}\right)$ values in ${\mathrm{Mo}}_6$${\mathrm{S}}_8$, Pb${\mathrm{Mo}}_6$${\mathrm{S}}_8$, ${\mathrm{Mo}}_6$${\mathrm{Se}}_8$, and Pb${\mathrm{Mo}}_6$${\mathrm{Se}}_8$ are 0.5, 1.7, 1.1, and 0.9 states/(spin Mo-atom eV), respectively, and show a strong correlation with $T_c$. States near to $E_{\mathrm{F}}$ are strongly confined within ${\mathrm{Mo}}_6$ octahedra.

A recently proposed approach—partial differential approximants—for analyzing power series in two (or more) variables for functions which exhibit singularities of multicritical, scaling character is tested by analyzing the susceptibility series for the bicritical point describing the Ising-Heisenberg-$\mathrm{XY}$ crossover in a three-dimensional classical ferromagnet. Encouraging results are obtained for the unbiased estimation of the bicritical point, of the multicritical exponents $\gamma$ and $\phi$, and of the slopes of the scaling axes.

We have searched for charge-$\frac{1}{3}$ and charge-$\frac{2}{3}$ particles produced with large $p_{\perp }$ in 400-GeV proton-Cu collisions. At $p_{\perp }=6.15\mathrm{}$ GeV/c, 4.9 × ${10}^4$ positive and 1.5 × ${10}^4$ negative unit-charge particles provided the normalization; no fractionally charged particles were found. The 90%-confidence-level upper limits for the invariant production cross sections per nucleon for positive and negative charge-$\frac{1}{3}$ particles are 5.1 × ${10}^{-39\mathrm{}}$ and 8.8 × ${10}^{-39\mathrm{}}$ ${\mathrm{cm}}^2$ Ge${\mathrm{V}}^{-2\mathrm{}}$, respectively; for charge-$\frac{2}{3}$ particles the respective limits are 1.3 × ${10}^{-39\mathrm{}}$ and 2.2 × ${10}^{-39\mathrm{}}$ ${\mathrm{cm}}^2$ Ge${\mathrm{V}}^{-2\mathrm{}}$.

We report measurements of the electroproduction of $\varphi$ mesons from hydrogen at $Q^2$ values of 0.23, 0.43, and 0.97 Ge${\mathrm{V}}^2$ with $\mathrm{}\left|t\right|\mathrm{}$ varying from 0.125 to 1.3 Ge${\mathrm{V}}^2$ at each $Q^2$ point. The data show no evidence for a $Q^2$ dependence of the slope of the $t$ distribution; the forward cross section falls with increasing $Q^2$ as the square of the $\varphi$ propagator; the decay angular distributions agree with the predictions of $s$-channel helicity conservation; and the ratio of the longitudinal to the transverse component increases linearly with $Q^2$.

32 dimuon and 11 trimuon events are observed in deep inelastic muon interactions at 150 GeV. The rate of diumuon production is greater than 5 × ${10}^{-4\mathrm{}}$ that of inclusive muon scattering. High-inelasticity trimuons occur at a rate one order of magnitude lower. These events are more numerous and the extra muons have qualitatively different production characteristics than muons expected from conventional sources.