Characterizing pressure ionization in ramp compressed Cobalt with electron induced fluorescence spectroscopy

The ionization stage constrains the effective Z and free electron density which plays a critical role in transport properties of HED matter. In spite of extensive theoretical and experimental efforts, there is still little consensus on pressure ionization under these extreme pressures and temperatures [1,2]. We have performed an experiment on OMEGA EP to measure ionization in compressed Co as a function of density, using the K shell fluorescence induced by hot electrons generated through short-pulse laser-solid interactions. The high pressure was achieved by ramp compression to keep the temperature below 2eV so as to rule out the effect of thermal ionization. When the Co density rises to about twice its initial value, a small red shift in the Co Kβ peak is observed, along with a shoulder at around 15eV below the main peak. Comparison of the measurement and predictions by different ionization models will be presented.

1. C. A. Iglesias, HEDP, 12, 5 (2014)

2. B.J.B. Crowley, HEDP, 13, 84 (2014)