In order to further explore the mechanism of direct-current glow discharge at low pressure

we proposed a two-dimensional DC discharge model based on local equilibrium approximation. Then we investigated the process of transition from normal to abnormal glow and their characteristics

and compared the numerical simulation results of abnormal glow with experiment results. The results show that

in normal glow discharge

when the voltage increases slightly

the current increases as a result of the increase of discharge region

the thickness of cathode fall decreases

and the negative glow becomes manifest; when the voltage further increases

discharge region covers the whole surface of cathode

and can distinguish cathode fall

negative glow

and positive column regions

then the normal glow translates to the abnorma

l glow. The electrical field in cathode fall is 3 200 V/cm when the voltage is 400 V. When discharge is abnormal glow and gas pressure is constant

the increase of voltage can not change the structure of discharge

the current increases and discharge enhances because of the increase of electron number density in the negative glow; when voltage is 400 V and the air pressure is in the range of 50

4

20 Pa

the discharge current increases with the gas pressure.