Continuum Hard-Photon K-Shell Yields From Z-Pinch Implosions: Present Status and Scaling to Higher Currents

• Published in: IEEE transactions on plasma science 2024-06, Vol.52 (6), p.2094-2116
• Main Authors: Velikovich, Alexander L., Ouart, Nicholas D., Dasgupta, Arati, Giuliani, John L., Tangri, Varun, Harvey-Thompson, Adam J., Schaeuble, Marc-Andre, Schwarz, Jens, Myers, Clayton E., Ampleford, David J., Vesey, Roger A., Jones, Brent
• Format: Article
• Language: English
• Subjects: Atomic measurements; Electrons; Ions; K-shell radiation; plasma pinch; Plasma temperature; Plasmas; Radiative recombination; recombination continuum; Temperature measurement; X-ray production; Z pulsed-power facility
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2024.3428372

The use of the recombination continuum for X-ray radiation production in Z-pinches is discussed as an option for generating high yields in the warm photon energy range, \hslash \omega \gt 10 keV. The free-bound direct-recombination continuum emission is an inherently weaker radiation production mechanism than the resonant-line emission. However, it is challenging, if at all possible, to heat stagnated Z-pinch plasmas with atomic numbers Z_{A} \gt 36 to temperatures above ~10 keV needed for efficient K-shell line emission in the warm photon energy range. As the atomic number of the load material increases from Z_{A} = 18 (argon) to Z_{A} = 26 and 29 (iron and copper, respectively), the scaling parameter determining the ratio of the recombination continuum to hydrogen-like line K-shell yield increases by a factor of 2-3. This indicates a possibility of using wire-array Z-pinch implosions on next-generation pulsed-power facilities (NGPPs) to produce significant continuum yields in warm photons. Such an option is feasible, provided that stripping substantial fractions of iron and copper ions at stagnation to an H-like state can be demonstrated. We analyze K-shell continuum yields measured in recent Z experiments with argon double-shell gas-puff and stainless-steel nested wire-array loads, with a view of scaling present-day results to higher driver currents.