Characterization of the COBRA triple-nozzle gas-puff valve using planar laser induced fluorescence

We present neutral density measurements of argon (Ar) injected into the 70 mm outer diameter, 24 mm axial length, outflow region of the triple-nozzle gas-puff valve fielded for gas-puff z-pinch experiments on the (1 MA, 100–200 ns) COBRA generator at Cornell University. Measurements are obtained by planar laser induced fluorescence of (λ = 266 nm, E = 80 mJ, Δt = 3 ns) frequency-quadrupled Nd:YAG laser light, absorbed by acetone dopant introduced into the Ar at 7% by pressure. Results are acquired 500μs after valve opening, the time of current initiation during z-pinch experiments. Number density plots are obtained across the Outer (O), Inner (I) and Center (C) puffs, with nozzle backing pressures {O:I:C} = {1:3:8}psia and {4:0:10}psia, delivering ‘uniform’ and ‘hollow’ profiles respectively. The total mass per unit length in these puffs is 22±0.4 μgcm⁻¹ and 47±1 μgcm⁻¹. Density measurement precision is ±5×10¹⁵ cm⁻³.