Effect of photoionisation on initial discharge in air under nanosecond pulse voltage

Effects of photoionisation on the development and electron runaway of the initial discharge in atmospheric air under nanosecond pulse voltage were studied via twodimensional particle-in-cell/Monte Carlo collision simulations.It was found that photoionisation has little effect at the beginning of the initial discharge.However,as the discharge channel gradually develops towards the anode,photoionisation shows greater impacts on the morphology of discharge but has little influence on the velocity of discharge development.Photoionisation does not appear to have a decisive effect on the growth trend of the highest energy of runaway electrons,but it does affect the change rate of the highest energy and overall distribution of electron energy,resulting in a higher proportion of energetic electrons.The difference in the distributions of the electron energy between the two cases,with and without considering photoionisation,can be attributed to the impact of photoionisation on the discharge morphology,which in turn distorted the electric field.The spatial density distributions of the electrons produced by photoionisation further explained the differences.The authors’results explicitly demonstrate the influence of photoionisation on the development and the electron runaway of the initial discharge under nanosecond pulse voltage,which provides more comprehensive knowledge for the atmospheric air gap nanosecond pulse discharge physics.

Range and similarity of hollow cathode discharge in argon

Hollow cathode discharge and micro-hollow cathode discharge have numerous applications in the fields of industry,medical treatment,environmental protection,and analytical chemistry.However,many of them lack the typical features of hollow cathode mode,especially the applications at atmospheric pressure.In order to investigate the underlying basic science of hollow cathode discharge,the hollow cathode discharge in argon was studied by experiments.The range for the operation of the hollow cathode mode in the argon-aluminum device was quantitatively determined to be from 0.8 to 4 Torr cm,no matter how small the cathode cavity is.The atmospheric pressure operation of the hollow cathode mode was realised with the aluminum cathode of a 50μm cavity.The hollow cathode discharges were consistent with Townsend similarity law when the anode was very close to the cathode and the value of p·D was chosen at the lower limit of the range for hollow cathode mode.In contrast,if the anode was moved a little bit far from the cathode and the value of p D was significantly increased,the results followed Allis-White scaling law.The reason for the deviation of Allis-White scaling law from Townsend similarity law was given.