Speaker
Description
Breakdown in DC gas discharges is primarily described by Paschen’s law. While Paschen’s law accounts for the flux balance correctly, the relation between the reduced electric field and the ionization coefficient is given empirically. In this study, we investigate DC breakdown using a full-fluid moment (FFM) model, which is benchmarked against a particle-in-cell/Monte-Carlo collision (PIC-MCC) model and a conventional drift-diffusion (DD) model. In the FFM model, the electron energy equation is solved consistently and inertial effects are accounted for. The results for argon show excellent agreement between FFM and PIC-MCC, including in the left branch (Pd<1 Pa m, where P is the gas pressure and d is the gap distance), where discrepancies with results obtained using a conventional DD model are observed. A double-valued breakdown curve is found using all models in the low Pd range, i.e., the left branch of the Paschen curve. Breakdown theory is revisited using a fluid formulation to derive modified breakdown conditions. The modified theory predicts a multivalued left branch, which is not predicted by the conventional Paschen’s law, and shows good agreement with computational results. Finally, the energy budget obtained from the fluid model is presented, showing a change from volumetric energy losses due to collisions at low reduced electric field to convective energy losses at smaller Pd where reduced electric field increases.
