Study of sausage instability in semiconductor plasma

As a perturbation of the adiabatically compressed linear pinch, a theory of the sausage instability is developed on the basis of the magnetohydrodynamic equations of motion and the particle conservation combined with Maxwell's equations. A dispersion relation of the instability and the explicit dependence of wave parameters on the fields are obtained by linearizing the equations for axially symmetrical harmonic perturbation. The critical field between a convective and an absolute instability is numerically obtained, and spatial growth rates associated with the instability are also derived in its convectively unstable region. The excitation of the sausage instability is made in an impact ionized plasma of n-InSb. The linear pinch effect of the samples is confirmed through the magnetic field dependence of current-voltage characteristics, and sinusoidal coherent oscillations are observed after a complete confinement of a pinch without an external magnetic field. Oscillation frequencies and currents on the threshold of excitations are obtained for various samples as a function of the applied electric field. The stabilization of instability by an axial magnetic field is also investigated theoretically and experimentally. The possibility of the stabilization is discussed through an evaluation of the magnetic Reynolds number in an impact ionized plasma pinch, and the critical magnetic field is derived from the hydromagnetic energy principle of the stabilization. Waveforms of the excited instability are observed under various axial magnetic fields in order to find the critical magnetic field for stabilization. The developed theories of the sausage instability on the dispersion relation and on the stabilization by axial magnetic fields are in good qualitative and quantitative agreements with the experiments. It is found that the sausage instability is excited in an impact ionized plasma of n-InSb and is explained well by the developed theory. (J.P.N.)