Ionization potential depression in dense plasmas
In plain words
Squeezing atoms close together makes their electrons easier to remove, lowering the energy needed to ionize them. Experiments disagree about how big this effect is, which matters for opacity and equation of state.
Precise statement
X-ray free-electron-laser measurements on solid-density Al (2012) favor the Ecker-Kroll model over Stewart-Pyatt, short-pulse laser-heated Al spectroscopy (Hoarty et al. 2013, https://doi.org/10.1103/PhysRevLett.110.265003) favors Stewart-Pyatt, and NIF X-ray scattering on imploded Be (Doppner et al. 2023, https://doi.org/10.1038/s41586-023-05996-8) shows more K-shell ionization than widely used depression models predict. Determine the ionization potential depression for Al, Mg, C and Be at solid and compressed densities and $T = 10\ \text{to}\ 500\ \mathrm{eV}$ with a validated ab initio method. An answer is a method that reproduces all existing datasets.
What would settle it
An ab initio calculation agreeing with the free-electron-laser, short-pulse laser and implosion data, confirmed by a new measurement at intermediate conditions.
Status in the literature
Unverified note
Path-integral Monte Carlo estimates of ionization and continuum lowering for warm dense hydrogen appeared in 2025 (arXiv:2503.14014).