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Recently, it was shown that certain 'smart' self-avoiding trails have end-to-end distances R 2 N ∼ N in three dimensions. Also, the corrections to scaling of R 2 N /N and the specific heat are qualitatively very similar to those for polymers exactly at the θ point. The question was thus posed whether they are in the same universality class as linear polymers at the θ temperature. We show that this is not the case since these trails show a first-order transition, instead of the second-order transition at the usual θ point. We argue that this is due to the fact that the 'smartness' of these trails implies that the renormalized n-body interactions vanish identically for any finite n 3. We conjecture that the qualitative similarity with recent simulations of θ polymers indicates that for n-body interactions the renormalized three-body interaction is small in real polymers.

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Measurements have been made with subnanosecond resolution of the azimuthal magnetic field spontaneously associated with plasmas produced by high-intensity (1012–1014 W/cm2) 1-nsec-duration CO2 laser pulses. In addition to a distinct dependence on background argon gas pressure, it is found that the magnetic field displays a 1/r2 radial dependence, and its onset is synchronous with the initial formation of the plasma.

A novel pendulum design—hollow ballistic pendulum—is suggested for plasma momentum measurements. It has an advantage over the pendula used earlier in laser plasma experiments of being insensitive to a momentum of matter evaporated and scattered by the pendulum wall exposed to the plasma, which usually exceeds plasma momentum to be measured. Simple expressions describing pendulum performance are derived, and requirements of shape and size are established. Using this kind of pendulum in experiments on laser acceleration of thin foils made it possible to measure the momentum of accelerated foil with an accuracy of about 10%.