INSTABILITY OF A STRONG PULSE CURRENT IN A TUNGSTEN PLATE

The instability of a strong pulse current is observed in a plate of pu re tungsten. The instability appears at low temperatures if the plate is placed in a high magnetic field parallel to the current direction. The magnetic field of the alternating current in the sample is detecte d by making use of a Hall probe. The inherent frequencies of the insta bility currents are some tens of hertz. Their amplitude ranges up to a bout hundreds of milliamperes. The primary directions of the instabili ty fields are along the steady magnetic fields, so that the instabilit y currents have a component at right angles to the initial current dir ection. There is a threshold value of the amplitude of the pulse curre nt at the beginning of instability. It has been found that the thresho ld value depends on the steady magnetic induction and is reduced signi ficantly when the induction increases. The amplitude of the instabilit y currents under study exhibits features of the dynamical chaos regime . The conversion into the chaos regime is effected by the formation of turbulent time intervals intermittent with laminar time intervals. It was found experimentally that the occurrence of the current instabili ty is accompanied by ultrasonic oscillations. The observed instability is attributable to the fact that the magnetic field of the current pu lses changes the trajectories of electrons. A set of equations has bee n proposed in order to explain the oscillatory behaviour of the fields of instability. This set contains two differential equations of parab olic type like the distributed parameter system with diffusion.