I-V analysis for nuclear-excited low-temperature plasmas in porous metals

We demonstrate how a high surface-to-volume ratio porous electrode structure within an ionizing radiation field generates a nuclear-excited low-temperature plasma source. In a foundational experiment, we compared the I-V characteristics of two electrode systems comprised of: (1) open-cell reticulated copper foam discs (pore radius similar to 500 mu m) and (2) solid copper discs. Both systems were held at 2 atm neon and irradiated in a nuclear reactor under steady-state operation. The primary source of plasma ionization was electrons derived from reactor gamma-rays; the secondary source was electrons from the beta - decay of Cu-64 and Cu-66 formed by the capture of thermal neutrons. The two electrode systems exhibited identical I-V proportionality for applied voltages between 2 V and 5 V, evidencing a sheath structure evolving within the copper foam discs. The energy fraction absorbed in the gas per unit electrode mass was 20%-70% greater for the porous electrode than for the solid electrode, corresponding to a factor of 3.5 increase in the specific ion output current [A g(-1)]. The plasma densities achieved in the porous and solid electrode systems were estimated to be (3.2-3.9)x10(9) cm(-3) and 7.1x10(9) cm(-3) respectively, assuming a spatially independent density profile and approximately ambient electron temperature.