Laser initiated spark development in an air gap.

Area of Science:

• Plasma physics
• Electrical engineering
• High-speed imaging

Background:

• Understanding spark development is crucial for applications like pulsed power and plasma processing.
• Previous studies have focused on macroscopic phenomena, with limited temporal resolution for initial stages.
• Metal vapor jets and prechannel formation are key but poorly understood aspects of spark breakdown.

Purpose of the Study:

• To investigate the initial stages of spark development using high-speed imaging.
• To elucidate the role of the metal vapor jet and prechannel in breakdown initiation.
• To characterize the temporal evolution of the spark channel during the high-current phase.

Main Methods:

• Utilized 20-nanosecond (nsec) image converter photography for high-temporal-resolution imaging.
• Studied spark development in a system involving a metal vapor jet and a counterelectrode.
• Initiated breakdown using a z-axis, laser-induced filament.

Main Results:

• Observed a diffuse and transparent prechannel bridging the metal vapor jet and the counterelectrode.
• Found that the prechannel inhibits cone-shaped jet development as gap voltage increases.
• Demonstrated that the final breakdown is triggered by a laser-induced filament expanding within ~10 nsec.

Conclusions:

• The prechannel plays a critical role in modulating spark development before final breakdown.
• Laser-induced filamentation provides a precise trigger for the high-current thermalization phase.
• The observed spark evolution aligns with theoretical models of initial spark channel thermal expansion.