DIAGNOSING PLASMA CONDITIONS IN TARGETS IRRADIATED BY INTENSE LIGHT ION BEAMS USING K α SATELLITE LINE INTENSITY RATIOS

Abstract

The characteristics of K α satellite line emission generated in intense light ion beam experiments is investigated. Inner-shell X-ray lines are emitted from moderate-temperature ( T∼10 1–10 2 eV) plasmas as 2p electrons of the target ions fill in K-shell vacancies created by beam ion-impact ionization. We focus, in particular, on the utilization of line intensity ratios from He-like and Li-like ions to diagnose target plasma temperatures and densities. Although the K α transitions for the He-like and Li-like atomic systems are the same as those in laser-produced and Z-pinch plasmas, the populating mechanisms for their upper states are completely different. That is, the upper states are populated from lower ionization stages by ion-impact ionization. This enables diagnosis of plasmas in the 10–100 eV temperature regime using the extensive instrumentation developed for X-ray crystal spectroscopy. Target plasma characteristics are simulated using a one-dimensional collisional-radiative equilibrium model in which atomic level populations are computed by solving multilevel statistical equilibrium equations self-consistently with the radiation field and ion beam properties. We utilize atomic models which include for all ionization stages a detailed treatment of autoionization states which have K-shell vacancies. Results are presented for Li beam-heated Al and Cl plasmas and proton beam-heated Al plasmas. We find that, as in the case of laser-produced plasmas, the He-like intercombination-to-resonance ratio provides a good density diagnostic. However, because the He α line is produced in ion beam-heated plasmas with a relatively low degree of ionization, it is less susceptible to resonant self-absorption effects as compared to laser plasmas. In addition, the Li-like satellite line structure is significantly different for plasmas heated by ion beams. Unlike laser-produced plasmas, the Li(dabc) and Li(qr) lines tend to be more intense than the Li(kj) lines. Because of this, we find the Li(dabc)-to-He α ratio to be a good temperature diagnostic for intense light ion beam experiments. We also discuss the effects of beam-induced multiple ionization, photoionization, and resonant self-absorption on the line ratio diagnotics.