The paper presents a comparative study of a spark discharge evolution in nitrogen for cases of its isothermal and adiabatic compressions. A numerical model of a spark channel expansion which was previously tested in a wide range of spark discharge energies was used for this purpose. The model takes into account electric circuit parameters, gas-dynamic expansion processes, thermal gas ionization, non-equilibrium chemical reactions, electron heat transfer and radiation. The initial pressure of adiabatically and isothermally compressed discharge gas was varied in a range from 1 to 20 atm. A capacitor with capacitances of 0.1 and 0.01 μF and a circuit inductance of 2 μH were applied in the calculation. The charge voltage was 30 kV. An influence of initial gas pressure on energy deposited by spark discharge, the efficiency of spark energy deposition, the parameters of the shock wave generated by the spark discharge, the efficiency of the discharge-to-radiation energy conversion and the resistance of the spark channel were finally evaluated. A correlation coefficient was introduced to reflect the initial pressure influence on the energy deposition. The coefficient can be used to imitate an equivalent spark load for any initial pressure.

A study of the influence of the discharge gap length and the initial gas pressure on the energy deposition into the discharge channel was done. The study was conducted at the same total discharge energy. It is experimentally shown that the connection of the voltage probe to the discharge circuit significantly affects the discharge current. The determination of the energy deposited into the spark channel is based on the results of numerical simulation of the spark channel development. Experimentally measured discharge currents at different pressures and the gap length were used as initial data for the calculation. Based on the obtained results, it is determined which of the factors (the initial pressure or the gap length) has the strongest influence on the energy input into the spark channel.