The earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line (about 10RE) which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths (less than 1 km). These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. In the second part of the paper a number of models of microscopic turbulence will be introduced into a large scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, we will compare the effect of a double layer electric field which scales with the plasma temperature and Debye length with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than the resistive model leading to the possibility of narrow, intense current structures.

We report on our work to simulate auroral double layers (DL's) with ‘realistic’ particle-in-cell models. An early model simulated weak DL's formed in a self-consistent circuit but under conditions subject to the ion-acoustic instability. More recent work has focused on strong DL's formed when currentless jets are injected into a dipole magnetic field.

The evolution and long-time stability of a double layer in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-layer potential structure. A simple model is presented in which this current re-distribution is effected by anomalous transport based on electrosatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-layer potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.

The possibility of an X-ray laser by irradiation of muon beams on a thin rod of deuterium-tritium mixture is discussed. The excited state of dtμ-mesomolecules (J, v) = (1, 0) can be induced to make radiative chain transitions with photon energy of 90 eV to the ground state (0, 0), evacuated by fusion.

The work proposes a straightforward method for determining the nuclear reaction cross sections at extremely low energies (E ≃ 1–100 keV) on the basis of the measurements of the relative yield of fast particles which are products of the nuclear reactions in a target under laser compression. On the other hand, the proposed method makes it possible to find the averaged form of the ion velocity distribution function if the low-energy behaviour of the respective cross sections is known.

Driven stimulated Brillouin rescattering, obtained by multiline laser light, each satellite line downshifted by twice the acoustic frequency ωs, is an efficient way to reduce stimulated Brillouin reflection (Colombant et al. 1983; Montes 1985). For long enough interaction lengths the nonlinear dynamics leads to optical turbulence. We consider a six wave coherent model whose wave frequencies are ω1 and ω3 = ω1 − 2ωs for the principal and auxiliary pump waves, ω2 = ω1 − ω2 and ω4 = ω1 − 3ωs for the backscattered waves, and ωs for the forward- and backward-traveling sound waves. The sound wave is weakly damped and its velocity is neglected (limit cs/c = 0). The space-time evolution is studied numerically. The model depends upon several parameters of nonlinearity. Increasing the interaction length L we observe: (1) a stationary regime for L smaller than a critical value Lcrit; then (2) an oscillatory behaviour appears through a Hopf bifurcation at L = Lcrit which becomes (3) more and more anharmonic and (4) finally chaotic for large L.