Time-Resolved Plasma Density Profiling with Two-chord Heterodyne Laser Interferometry and Quadrature Demodulation in a Z-Pinch Fusion Device

Nuclear fusion requires sufficiently hot and energetic ionized plasmas to overcome Coulomb repulsion between nuclei and reach critical densities. In sheared-flow-stabilized Z-pinch fusion devices, axial current flow produces a self-confining magnetic field that compresses the plasma to such densities. However, this plasma’s behavior is susceptible to kink and sausage instabilities that dramatically decrease its confined density and hinder fusion reactions. In order to understand the potential of a plasma to facilitate fusion, it is essential to measure corresponding time-varying plasma densities underlying its approach toward critical density, along with internal instabilities that induce weakened interactions. This study uses a two-chord heterodyne Mach-Zehnder laser interferometer (IF) with quadrature analog demodulation to observe temporally dynamic line-integrated electron density of ionized hydrogen within a Z-pinch fusion device. With coaxial (z-axis) chords, Abel inversions are used to reconstruct a radial plasma density profile identifying self-compression within the current. Additional imaging diagnostics used in tandem reveal pinch radius and subsequently both plasma temperatures and IF impact parameters. Together, these diagnostics can parametrize a plasma that satisfies the fusion triple product of hot, dense plasma within a high-voltage pulsed power plant, progressing towards a positive Q factor.