The threshold field ~ is minimal at the plasma resonance point ~ = O: $,1, I/lO~2(Inua) , and it corresponds to the resonance instability due to the resonant ...
MAGNETIC INSTABILITY IN AN INHOMOGENEOUS PLASMA IN AN INTENSE ELECTROMAGNETIC WAVE UDC 533.933
A. I. Al'ber, A. A. Zharov, T. M. Zaboronkova, I. G. Kondrat'ev, and E. N. Krotova
Parametric magnetic instability has been examined for a collisional inhomogeneous plasma in a strong electromagnetic wave; the spatial inhomogeneity causes the instability region to localize near the plasma resonance. The space-time evolution in the magnetic field is substantailly dependent on the pumping wave amplitude. Numerical calculations have been made on the behavior of Gaussian initial magnetic-field perturbations with various scales, which illustrate the model.
i. A quasistatic magnetic field can be excited in a plasma that interacts with a highfrequency electromagnetic field because of nonlinear eddy currents, which can occur in two ways in accordance with the conditions. Either one has a constantly acting source of that field, which leads to the field gradually strengthening over time [i], or the corresponding current arises because of a seed field, which causes [2] an exponentially rapid increase: aperiodic parametric instability. Those studies relate to a spatially homogeneous plasma. Here w e consider the magnetic instability in a weakly inhomogeneous plasma: k0s = (o~0/c)s = (2~/%0)s >> 1 (m0 and %0 are the frequency and wavelength of the incident high-frequency field, while s is the characteristic plasma inhomogeneity scale). The spatial inhomogeneity localizes the instability region, which is related to the inhomogeneity in the amplitude of the electric field in the pumping wave, which occurs near the plasma resonance. We examined the hydrodynamic diffusion state in that instability, which involves the assumption that the electron mean free path s is small by comparison with the wavelength in the plasma %: s ~=,z2 one will ultimately get as before that comparatively small-scale perturbations develop in the r e g i o n w i t h negative diffusion. 4. We now give numerical solutions. We examine the behavior of initial (seed) Gaussian perturbations with various scales near the plasma r~sonance for various pumping amplitudes. To reguliarize the computer formulation when ~ > ~ax , we incorporate phenomenologically the weakly nonlocal coupling between the current and the quasistatic electric field [5]. That weak low-frequency spatial dispersion hardly affects the results for comparatively small pumping amplitudes ( ~ < ~ a z ) ' and also in the initial stage (~ < ~*) for large amplitudes, but it eliminates the explosive instability for x~ T *. Figure 1 shows the behavior of small-scale initial perturbations in pumping fields corresponding to
