Quasisteady magnetic fields could be generated in laser-produced plasmas with high-frequency electromagnetic radiation through wave–wave and wave–particle interactions in the vicinity of the critical point. The behavior of self-generated magnetic fields can be described by nonlinear coupling equations. It is analytically indicated that self-generated magnetic fields are modulationally unstable with respect to the uniform state of a plasma; such an instability would localize the magnetic fields within narrow regions near the critical surface. The theory is supported by a detailed comparison with experiments in laser-produced plasmas.

Using a kinetic description, the relativistically strong Langmuir turbulence is investigated, which has considered the nonlinear wave–wave, wave–particle interactions and the relativistic effects of electrons. The relativistic Zakharov equations have been obtained. On the basis of these equations, dynamics of collapse has been studied. It is shown that the field strength of relativistic Langmuir plasmons will increase and the ponderomotive expulsion of particles gives rise to the formation of density caviton during the collapsing, which is useful for understanding the natural structural element of relativistically strong Langmuir turbulence

Abstract. It is shown that the transverse plasmon field is modulationally unstable in the Lyapunov sense, leading to a self-similar collapse of the magnetic flux. Such a collapsing magnetic instability is analyzed in both cases of magnetohydrodynamics and kinetic plasma physics, with their applications to solar intermittent flux and anomalous viscosity in accretion disks, respectively. In the first case, we find that the equilibrium between the ponderomotive force and the Lorentz force in a current sheet gives rise to a more spatially intermittent collapsing magnetic flux, very similar to a turbulent pattern; as a result, the 0.1 kG flux cells with larger scales emerging at the surface from the solar interior become shredded and the flux is thereby contracted rather quickly to a small scale of the order of 100 km as well as concentrated into a 1-2 kG state. In the second case, based on Vlasov equations and Maxwell equations, the collapsing feature of the self-generated magnetic field from transverse plasmons is investigated on rather small scales of the motion or electric current in accretion disks; as the effects of the intermittent magnetic flux, an anomalous magnetic viscosity and an anomalous resistivity are indicated, with a different magnetic Prandtl number, which is not very sensitive to the temperature T .

The behavior of magnetic fields generated by high frequency transverse plasmons in relativistic plasmas can be described by a set of nonlinear coupling equations, which has considered the nonlinear wave-wave, waveparticle interactions and the relativistic effects of electrons. Modulational instability of the spontaneous magnetic fields is investigated on the basis of the nonlinear coupling equations. Analytical and numerical results indicate the self-generated magnetic fields are modulationally unstable and will be localized in a narrow region. The characteristic scale and maximum growth rate of the magnetic fields depend on the average Lorentz factor of electrons and the energy density of transverse plasmons. The relativistic effects of electrons will enhance the self-focusing of magnetic fields.

Numerical simulations of three-wave interactions among Langmuir, ion-acoustic, and electromagnetic waves by means of an efficient algorithm developed here for solving full Zakharov equations show that total electric field collapses if the electrostatic field collapses when plasma temperature is much less than 0.5 MeV and thus relativistic effects can be neglected, and that the electromagnetic wave energy generated in the high-temperature Langmuir collapse comes to no less than one-tenth of the Langmuir wave energy even if the mean intensity of the collapsing wave packet increases by a factor of less than 5.