Similarity of gas discharge in low-pressure argon gaps between two plane-parallel electrodes

The similarity of gas discharge in low-pressure argon gaps between two plane-parallel electrodes was investigated by experiments,numerical simulations and theoretical analysis.It was found by the experiments that the breakdown voltages depend not only on the product of gas pressure and gap length,but also on the aspect ratio of the gap,i.e.U_(b)=f(pd,d/r).It was theoretically proved that U_(b)=f(pd,d/r)is also a special case,the non-uniform electric field between plane-parallel electrodes,of similarity theorem of gas discharge.It was found by the experiments that there exist similar glow discharges only in two gaps with a limited scaled-down factor k.By theoretical analysis,it was explained that the forbidden processes such as the stepwise ionisation and the inelastic collision of the second kind violate the similarity of discharge as k increases,which was verified by the numerical simulations of the discharges with or without these two forbidden processes taken into account.