UC San Diego

Vacuum gap breakdown mechanisms for many geometries, such as sphere-sphere, plane-plane, and point-plane, are well understood and documented.[13] To date, no detailed analysis of a coaxial electrode geometry has been performed. This work is motivated by the need to better understand the mechanisms by which breakdown initiation occurs in a coaxial gap over a few nanoseconds to a few microseconds at tens of kilo-volts over gap sizes up to 1.5 mm, especially considering how common the use of a coaxial gap is in high voltage power lines of large pulsed power machines.

Of specific interest is the evolution of the magnetic field in time and space along the gap and how asymmetries about the azimuth of this gap influence this evolution. Asymmetry in breakdown about the azimuth could be responsible for non-uniform distributions of voltage and current which could lead to early time scale instabilities of a load at the termination of a transmission line.

This work is relevant to larger pulsed power machines that presently make use of a µm high voltage coaxial vacuum gap in the power feed, such as the MagLIF [14] design on Sandia’s Z-machine. On these larger machines, the cathode gap power feed cannot be observed and is usually not directly monitored by diagnostic tools. Often a direct observation of vacuum gaps is not feasible, a comprehensive method to observe and influence the evolution of the magnetic field and current density would prove beneficial.