Features of DC gas breakdown between electrodes with variable gap

The results of experimental researches of gas breakdown features between electrodes with variable gap are presented. The breakdown curves of the discharge between the cylindrical electrodes with a hemispherical apex were measured in the range of nitrogen pressures of 0.03 – 200 Torr for different values of the interelectrode gap. It is established that on the curves of the dependence of the breakdown voltage on the gas pressure there are long horizontal sections for distances smaller than the diameter of the electrode. The principle of gas breakdown curve formation between electrodes with variable gap is formulated: the breakdown curve consists of three parts, including horizontal section with minimum voltage, where gas breakdown occurs with the optimal path, which is automatically selected so that the breakdown voltage is the lowest (Stoletov's point). A numerical theoretical model has been developed that allows calculating the breakdown voltage of a gas between electrodes of arbitrary curvilinear shape. It is shown that in the case of flat electrodes for a sufficiently large distance between the electrodes, the Paschen similarity law is not satisfied. It is concluded that the reason for this is the loss of charged particles on the dielectric walls of the discharge chamber due to radial diffusion and the defocusing geometry of the electric field lines. For the system with hemispherical electrodes it is shown that the physical reason for the formation of a horizontal section on the breakdown curve is the change in the breakdown path when the gas pressure changes, diffusion processes expand the breakdown channel, and the trajectory of particles in a curved electric field does not repeat the shape of the force line due to the inertia of motion. It is shown that due to the accumulation of surface charge, the losses of charged particles are reduced, and breakdown becomes possible at much lower voltages.