A bit offtopic to this thread but still related to UDH formation: What would be the options for formation of UDH using plasma technology?
Hydrogen plasma is an excellent source of atomic Hydrogen (think of atomic H welding equipment).
Combining this with the presence of suitable catalyst(s) it would be possible to form UDH, right? (having Safire project in mind, and early demo of Andrea Rossi, showing plasma device).
Possibly a dusty environment will work better. Condensation to Rydberg matter (first) and the ultra-dense form (after) releases energy and this condensation energy must be removed, otherwise the clusters will revert back to their higher form. The solid particles (or other surfaces) where adsorption/desorption takes place would act as an energy sink.
This is in part explained in a 2002 paper in reference to Rydberg matter (paywalled), for example in this excerpt:
or briefly mentioned more recently for example in the review paper relatively to the ultra-dense form, where the issue is more difficult:
Quote[...] As discussed above, the formation of H(0) goes over states H(l) and down to H(1). The transfer from H(1) to H(0) is quite complex, since the energy given off by the H(0) cluster formation will mainly be taken up as rotational energy in the clusters. Due to their super properties, they will not easily transfer or lose this energy to the surroundings. This process is included in figure 12, and this figure indicates that the higher state H(1) will be reformed, if the excess condensation energy cannot be removed. Thus, the spontaneous condensation to H(0) is normally a slow process.