Some Nonlinear Properties of Electron-Hole Plasmas Sustaining the Helical Instability

Abstract

Electron-hole plasmas in $p$-InSb are driven far beyond the threshold of the helical instability into the non-linear region by applying axial magnetic fields $B$ much greater than the threshold fields $B_{\mathrm{th}}$. While the plasma is immersed in a static $B$ three fundamental properties of the plasma, namely the electric-field strength $E$ sustained in the plasma, the self-magnetic field $B_h$ produced by the rotating plasma, and the frequency of helical oscillations $f$, are measured. As $B$ is increased from zero, $E$ first decreases until $B=B_{\mathrm{th}}$; then $E$ rises with a slope and magnitude greater than those associated with the decrease. The quantity $\frac{B_{h}R}{I_T}$, where $I_T=\mathrm{total}\mathrm{current}$ and $R=\mathrm{radius}$, possesses a maximum as a function of $\mathrm{BR}$. At constant $I_T$, $f$ exhibits a trend to increase with increasing penetration into the nonlinear region until the onset of turbulence; however, $f$ is a nonmonotonic function of $B$. $E$ is also measured while the plasma is immersed in a magnetic field varying with time at a rate $\dot{B}$. The most striking result is the splitting of the $B_{\mathrm{th}}$ into two branches with increasing $\dot{B}$ as observed by the occurrences of two minima in the $E$ versus time curves. Comparisons are made among all these results and those available on the nonlinear properties of electron-ion plasmas, both experimental and theoretical.