The comprehension of electromagnetic perturbations of electronic devices, due to air plasma-induced electromagnetic field, requires a thorough study on air plasma. In the aim to understand the phenomena at the origin of the formation of non-equilibrium air plasma, we simulate, using a volume average chemical kinetics model (0D model), the time evolution of a non-equilibrium air plasma generated by an energetic X-ray flash. The simulation is undertaken in synthetic air (80% N2 and 20% O2) at ambient temperature and atmospheric pressure. When the X-ray flash crosses the gas, non-relativistic Compton electrons (low energy) and a relativistic Compton electron beam (high energy) are simultaneously generated and interact with the gas. The considered chemical kinetics scheme involves 26 influent species (electrons, positive ions, negative ions, and neutral atoms and molecules in their ground or metastable excited states) reacting following 164 selected reactions. The kinetics model describing the plasma chemistry was coupled to the conservation equation of the electron mean energy, in order to calculate at each time step of the non-equilibrium plasma evolution, the coefficients of reactions involving electrons while the energy of the heavy species (positive and negative ions and neutral atoms and molecules) is assumed remaining close to ambient temperature. It has been shown that it is the relativistic Compton electron beam directly created by the X-ray flash which is mainly responsible for the non-equilibrium plasma formation. Indeed, the low energy electrons (i.e., the non-relativistic ones) directly ejected from molecules by Compton collisions contribute to less than 1% on the creation of electrons in the plasma. In our simulation conditions, a non-equilibrium plasma with a low electron mean energy close to 1 eV and a concentration of charged species close to 1013 cm−3 is formed a few nanoseconds after the peak of X-ray flash intensity. 200 ns after the flash application, the electrons are thermalized and their concentration has decreased from about 1013 cm−3 down to about 1012 cm−3 leaving positive and negative ionised species and atomic radicals whose recombination characteristic times are much longer.

The contribution of the electromagnetic field to the electric response of a circuit exposed to high x-ray flux is quantified based on a novel approach which combines both experimental and numerical tools. First, we describe the method used to quantify the ionizing and electromagnetic stress induced by the x-ray beam in free space as well as on the target circuit. Next we show the perturbation resulting from the x-ray irradiation of an analog circuit. Also, we present the effect of an electromagnetic plane wave on the electric response of the circuit. Based on the comparison of experimental results, we demonstrate that electromagnetic fields coupling resulting from photoelectrons produced by the x-ray/circuit interaction is similar to the coupling induced by an external electromagnetic plane wave.Index Terms-Monte-Carlo calculations, particle-in-cell calculations, system generated electromagnetic pulse, transient radiation effects on electronics.