Evidence of shock-reflected ions and azimuthal rotation in gas-puff z-pinch implosions on COBRA*

Gas-puff z-pinch implosions are characterized by the formation of a dense annular plasma shell that is driven to the axis by a magnetic piston. The thickness of the shell and the velocity, temperature, and density profiles within have been shown to depend on the initial puff density, gas species, and axial magnetic field strength [1, 2]. However, in all cases tested on the 1-MA, 220 ns COBRA generator, Thomson scattering measurements indicate the presence of non-thermal spectral broadening that is consistent with dissipative turbulence driven by unstable plasma waves in a collisionless shock [2]. This observation aligns with the fact that the calculated collisional stopping length of upstream ions exceeds the shell thickness in these cases [2]. Here, we present Thomson scattering measurements of the shock layer for triple nozzle gas-puff implosions with varying levels of imposed axial magnetic field. The results show evidence of shock-reflected ions (i.e., a shock precursor) as well as azimuthal rotation of both precursor ions and the plasma in the imploding shell.  These observations corroborate previous reports of self-induced azimuthal rotation in gas-puff z-pinch implosions [3], offering new insights into the complex dynamics of these systems.

[1] E. S. Lavine, et al., Phys. Plasmas 28, 022703 (2021)

[2] E. S. Lavine, et al., Phys. Plasmas 29, 062702 (2022)

[3] M. Cvejić, et al. Phys. Rev. Lett. 128, 015001 (2022)