Nonlinear oscillations and current disruptions caused by the negative differential resistance of an electric double layer

The self-oscillations excited by the negative differential resistance of a strong double layer are investigated in a magnetized plasma column in triple plasma machine. The oscillations are excited if the current circuit has a resonance frequency with a period less than about an ion transit time along the plasma column. It is found that the oscillations can be described by a generalized van der Pol equation and be classified according to the parameter ε = (L/C)1/2/Rm where Rm is the absolute value of the minimum negative differential resistance and L and C are the inductance and capacitance of the current circuit. For ε << 1, the voltage oscillations are harmonic, and it is found that they are approximately described by the asymptotic solutions by Bogoliubov and Mitropolsky. For ε >> 1, the oscillations assume the form of current disruptions with very large voltage spikes concentrated to the double layer. (author)