In a series of experiments using two-, four-, and eight-beam 10.6-jum-laser irradiation of a variety of target geometries, a significant amount of energy was found to be deposited in regions remote from the focal spots. The deposition patterns can be predicted with a self-generated magnetic field model. PACS numbers: 52.50.Jm Lateral transport of energy away from laser focal spots can play an important role in redistributing energy deposition in laser-fusion targets. Work has been reported investigating the qualitative 1 and quantitative 2 nature of this transport. Recently, using a plasma simulation, Forslund and Brackbill 3 have identified convective transport of electrons in self-generated magnetic fields as an important mechanism for surface transport in laser-irradiated foils. In one simulation with a laser intensity of 5 x 10 13 W/cm 2 in a 60-jum spot and a hot-electron temperature of 20 keV, peak fields of the order of 1 MG were calculated. The calculation has not been performed at higher intensities comparable to those used in experiment (~10 16 W/cm 2 ) because the code does not handle the relativistic effects of the high-energy electrons generated at these intensities. In general, the ratio of electron to magnetic field pressure is of order 1 in a magnetized sheath whose thickness is large compared with the electron gyroradius. This Letter presents experimental evidence for the nonuniformity of energy deposition predicted by the magnetic field model in a variety of target geometries progressing from flats to cylinders to spheres. From the simulations, a simple qualitative moddel has been developed. Briefly, the model describes lateral energy transport by electrons in magnetic fields generated at the periphery of the laser spot by lateral temperature gradients in the corona. These gradients are maintained by electrons confined and drifting in the magnetic field, resulting in the convective transport of energy from the beam spot to the edge of the magnetized region. The interaction of the magnetic field and electrons produces a thermal magnetic wave 4 which propagates across the surface until disrupted by fringing fields at the target edge or by destructive interference with the wave propagating from an adjacent beam.

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We have measured differential cross sections for both a + p and P -p elastic scattering at incidentpion kinetic energies of 30, 50, 70, and 90 MeV in the center-of-mass angular range between 50" and 150". The experiment detected pions scattered from a liquid-hydrogen target with multiwire proportional chambers and scintillation-counter range telescopes. The relative accuracy of each angular distribution is better than 5%, while the absolute cross sections have uncertainties of 4% to 25%. Our results for the absolute cross section for ~+ p scattering at 30 and 90 MeV are inconsistent with previous measurements. Our P -p measurements comprise the first extensive set of precision differential cross sections below 90 MeV.

We present measured angular distributions for n+-elastic scattering at 30 and 50 MeV from selected targets with A = 12 to 208. These angular distributions were analyzed using a phenomenological optical potential of first-order form. The mass dependence of the potential strength parameters displays the isospin dependence expected from the free mN interaction.NUCLEAR REACTIONS Elastic scattering of 30 and 50 MeV~from 2C, 0, 4 Ca, +Zr, Pb. Ai~ular distributions: 25'«z,~& 160 . Optical model ana1-ysis of cross-section data.

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