Theory of electron current filamentation instability and ion density filamentation in the early development of a DPF discharge

• Main Authors: Guillory, J, Rose, D V, Lerner, E J
• Format: Conference Proceeding
• Language: English
• Subjects: ANODES; CATHODES; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPUTERIZED SIMULATION; CURRENT DENSITY; ELECTRIC CURRENTS; ELECTRON TEMPERATURE; ELECTRONS; EV RANGE 01-10; FILAMENTS; ION DENSITY; LAYERS; LIGHT IONS; MAGNETIC FIELDS; PERTURBATION THEORY; PLASMA; PLASMA DENSITY; PLASMA FOCUS; PLASMA INSTABILITY; PRESSURE RANGE KILO PA; TWO-DIMENSIONAL CALCULATIONS
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.3079729

Two-dimensional simulations of the initial stages of plasma formation in a dense plasma focus show the formation, in a few tens of nanoseconds, of a dense layer of plasma (ne~1018 cm-3,Te~3 eV) in a thin layer surrounding the insulator-covered central anode of the focus device, and carrying axially-directed current at rather high current density.Earlier work on the filamentation of dense cathode plasma in high-power diodes [1] seems to indicate that the anode plasma current layer in a dense plasma focus (DPF) device could be subject to the same instability, creating a growth of axially-directed filaments in the current density. The growth rate for resistive-thermal-driven filamentation, e.g. at 30 torr and ~3 eV electron temperature, exceeds the that due to non-thermal current (JXB) driving, and is determined by electron dynamics [1], so its evolution is quicker than the response-time of the ions.Nonetheless, with such a growing current-density perturbation as a seed and its increasing rippling of the azimuthal magnetic field as a driver, the ions will eventually take part in the azimuthal bunching, forming filaments in the ion density as well. The resistive-thermal-driven filamentation fields thus serve to 'hurry-up'the development of ion density filamentation, as shown approximately in the work presented here. This theory predicts, for light ions, a relatively early ('250 ns) development of visible filaments along the anode, perhaps even before the main rundown phase of the focus plasma motion, and these filaments may persist during the 'liftoff' phase of the current layer to form the rundown phase of the plasma front. This work is supported by Larwenceville Plasma Physics.