Ion and electron transport properties have been measured in a steady state, weakly turbulent plasma that was subjected to crossed E and B fields. The geometry permits quantitative measurements of electron and ion currents. The ion gyro radius is large compared to the apparatus dimensions. Measurements of the potential gradients, Hall currents, and ion velocity show that the ions are freely accelerated through the plasma by electrostatic forces. However, an ``anomalous diffusion'' of electrons is observed since the electron current across the magnetic field is much too large to be due to collisional diffusion. The plasma is weakly turbulent, consisting of a slowly rotating density concentration on which higher frequency fluctuations are superimposed. Electric field fluctuations are found that are correlated with the density variations so as to produce the ``anomalous diffusion'' via adiabatic E × B drifts. The magnitudes of these electric field and density variations are used to predict a net electron current that agrees with the direct measurements of this current. Reasonable agreement with the turbulent diffusion theory of Yoshikawa and Rose is obtained.

Injection and containment of unneutralized clouds of electrons has been accomplished with an azimuthally symmetric, toroidal, magnetic field. The confining magnetic field is produced within a conducting toroidal chamber. The induction of this magnetic field has been used to inject the electron cloud (inductive charging). Average electron densities of 4 × 109 cm−3 and peak electrostatic well depths of ≈ 400 kV have been achieved. Semiempirical correlations are given which show the inductive charging scheme to be governed by an electron energy restriction and finally limited by the occurrence of anomalous crossed field beam noise. Stable equilibria, without the necessity of a rotational transform have been observed for times in excess of 60 μsec. Correlation of the containment time observations with the predictions of a theoretical model for an ion-diocotron wave instability shows that the containment time is governed by the rate of ionization of the residual neutral gas (p > 10−7 Torr) in the apparatus. The correlation of theory and experiment appear to confirm the theoretical prediction that a significant degree of charge neutralization (in the range of 10-20%) can be stably contained. Interpretation of these results suggests that significant improvement in both electron cloud density and containment time should be possible.

We present results from the application of laser interferometry to the study of short-pulsed laser ablation of biological tissue. The mechanical response of tissue to laser-induced stress is examined under subthreshold conditions to determine its role in initiating the ablation process. A theoretical model is developed to relate this surface displacement to the pressure within the tissue and the mechanical properties of the tissue. In the experiment, a 7.5 ns pulse of 355 nm light was used to irradiate bovine shank bone, human meniscus, and an aqueous dye solution. Interferometric monitoring of the tissue surface was used to determine its motion after laser irradiation. The surface movement of bone was qualitatively consistent with the theoretical predictions of the model. The movement of meniscus and an aqueous dye solution showed additional features that are consistent with the growth and collapse of cavitation bubbles.

Using targets of H, D, Li, Be, C, Cu, and Sn, we have measured the energy distribution of scattered 7 rays at 45°, 90°, and 135°. In first approximation one would expect a scattering cross section given by the coherent addition of Thomson scattering amplitudes for Z free protons. Important deviations, probably of mesonic origin, are observed above 90 Mev. Below 70 Mev in complex nuclei there is an increase in cross section which probably results from nuclear resonance scattering. At small angles in the forward direction, we observe large numbers of inelastically scattered y rays, which apparently result from inner bremsstrahlung associated with electron pair production.

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