Ion stopping power in warm dense matter near the Bragg peak
In plain words
Fusion-born helium nuclei heat the fuel by slowing down in it, and how quickly they slow is set by the stopping power. Near the speed where slowing is strongest, theories for dense, partly degenerate matter disagree.
Precise statement
For alpha particles and protons with speed comparable to the electron thermal or Fermi speed (the Bragg-peak region) in DT, CH and carbon at density $1\ \text{to}\ 100\,\mathrm{g}/\mathrm{cm}^3$ and $T = 10\ \text{to}\ 1000\,\mathrm{eV}$, determine the stopping power $dE/dx$ to within 10 percent; Li-Petrasso, Brown-Preston-Singleton, quantum Lenard-Balescu, T-matrix and time-dependent DFT results differ most there. An answer is measurements in degenerate, strongly coupled conditions that discriminate among these formalisms.
What would settle it
Ion energy-loss measurements with independently diagnosed density and temperature in warm dense targets, at 10 percent precision near the Bragg peak.
Status in the literature
Measurements in moderately coupled implosion plasmas (Frenje et al. 2019, https://doi.org/10.1103/PhysRevLett.122.015002) tested several formalisms near the Bragg peak; data in strongly coupled degenerate conditions remain scarce.