I ran across a paper recently on lattice confinement fusion possibly taking place in the core of gas giants like Jupiter and Saturn, assuming that they have iron/nickel cores and includes deuterium. It was presented as a possible cause of Jupiter radiating more heat than it receives from the sun.
Deuterium fusion, sometimes with involvement of lithium, likely occurs in brown dwarfs, objects that do not have enough mass to start the proton-proton chain of fusion, as what occurs in the Sun. Brown dwarfs are typically below 0.08 solar masses, or between 15 and 80 Jupiter masses.
I think I might have read that article. IIRC the theory has something to do with there being enough pressure to generate metallic hydrogen or even hydrogen-lithium lattice structures. It changes the rules of physics
such that the physics is no longer plasma-based but more condensed-matter based.
A Pycnonuclear reaction in ultra dense condensed matter is a different fusion process in which density is the governing factor of the reaction rate. The crystalline lattice provides an alternative mechanism to reach higher density.