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

Abstract

We demonstrate how porous electrode structures with a high surface- to-volume ratio within an ionizing radiation field generate a nuclear-excited low- temperature plasma source. In a foundational experiment, we compared the I-V characteristics of two electrode systems: 1) open-cell reticulated copper foam discs (pore radius ∼ 500μm) 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 γ- rays. The secondary source of electrons was attributed to electrons from the β− 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 2V and 5V, 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) × 10^9 cm^−3 and 7.1 × 10^9 cm^−3 respectively, assuming a spatially independent density profile, and the electron temperature under these conditions was approximately ambient.