Femtosecond laser-induced breakdown spectroscopy in low-density gases relevant to pulsed power electrode desorption*

Sandia National Laboratory’s Z Pulsed Power Facility radially compresses electrical energy in space and time to deliver a peak current of 30 MA and peak power of 80 TW to a mm-scale Z-pinch fusion load. The transmission line electrodes near the machine center are rapidly heated by the 100 ns current pulse and thermally desorb 10¹⁵ cm^-3 gases comprising hydrogen, water, and various carbon-based contaminants. Field-emitted electrons dissociate and ionize these desorbed neutrals to form electrode gap plasmas that shunt MA-scale currents away from the fusion target. We report on our initial development of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) to measure desorption from pulsed power electrodes. We achieved 10¹⁴ cm^-3 detection capability and observed strong molecular signals in single-shot fs-LIBS measurements of gas cells containing H₂, H₂O, CH₄, and CO₂.