| Popis: |
The similarity law was not always valid because of the occurrence of the forbidden discharge processes, such as the low pressure recombination, stepwise ionization and the charge exchange between a fast neutral particle and an ion1−3. In order to study the properties of large-scale glow discharge using the extrapolation method, the validity of similarity law of glow discharge at low pressure was examined by numerical simulation. In this report, two similar discharge gaps with electrodes in parallel plate configuration were established and the gap length d, electrode radius r and gas pressure p were set to meet the relations of p 1 d1=p 2 d 2 , p 1 r 1 =p 2 r 2 , respectively. The pressures were 1torr and 10torr and the scale ratio of the two gaps was 10∶1. The simulation investigated the discharge processes with and without forbidden processes in two similar gaps, respectively. The results indicate that the discharges were typical normal glow discharge in the two gaps and the cathode voltage fall was about 100 volts which is consistent with the known results. The physical parameters (such as the electric field and electrical potential, the electron density, ion density, electron temperature) were all obtained. By comparing the physical parameters between the two similar gaps, it was found that the discharge properties without the forbidden processes were in good agreement with the similarity law, however, the obvious deviations (10% or so) were found in the discharge with the forbidden processes. |
