Dynamic formation of stable current-driven plasma jets.

Instabilities play a prominent role in determining the inherent structure and properties of magnetized plasma jets spanning both laboratory and astrophysical settings. The manner in which prominent unstable modes dynamically evolve remains key to understanding plasma behavior and control. In astrophysical phenomena, self-similar jets are observed to propagate over vast distances while avoiding breakup caused by unstable mode growth. However, the production of stable dense plasma jets in the laboratory has been limited by the onset of unstable modes that restrict jet lifetime, collimation, and scalability. In this work, we visualize the formation of stable laboratory-generated, dense, super-magnetosonic plasma jets in real time, and we identify an underlying mechanism that contributes to this behavior. The current-driven plasma jets generated in our experiments form a flowing Z-pinch, which is generally unstable to the m = 1 kink instability. Our results indicate that a stable dense plasma jet can be maintained for timescales over which a steady pinch current can be sustained, even at levels which would otherwise lead to rapid unstable mode growth and resultant pinch disassembly.

Evidence of Branching Phenomena in Current-Driven Ionization Waves.

This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model.

A fast rise-rate, adjustable-mass-bit gas puff valve for energetic pulsed plasma experiments.

A fast rise-rate, variable mass-bit gas puff valve based on the diamagnetic repulsion principle was designed, built, and experimentally characterized. The ability to hold the pressure rise-rate nearly constant while varying the total overall mass bit was achieved via a movable mechanical restrictor that is accessible while the valve is assembled and pressurized. The rise-rates and mass-bits were measured via piezoelectric pressure transducers for plenum pressures between 10 and 40 psig and restrictor positions of 0.02-1.33 cm from the bottom of the linear restrictor travel. The mass-bits were found to vary linearly with the restrictor position at a given plenum pressure, while rise-rates varied linearly with plenum pressure but exhibited low variation over the range of possible restrictor positions. The ability to change the operating regime of a pulsed coaxial plasma deflagration accelerator by means of altering the valve parameters is demonstrated.