Comparison between measured and simulated electron density of air plasma generated at atmospheric pressure by multi-MeV pulsed X-ray

Summary form only given. This contribution is devoted to the analysis of an air plasma generated by a multi-MeV pulsed X-ray in order to better understand the plasma-induced electromagnetic perturbations near electronic devices. A wave guide filled with atmospheric pressure air is irradiated by a high flux of the pulsed X-ray in order to generate an air plasma. To determine the electron density, we measured the absorption of an electromagnetic wave during its waveguide crossing. The measured electron density is then obtained by using the formalisms governing electromagnetic wave propagation in air plasma. The propagation equation needs the knowledge of the time evolution of the mean electron energy. The latter is obtained from a reaction kinetic model allowing more particularly to study the evolution of the density and mean energy of the energetic electrons self-generated during the collisions of X-rays with air molecules. This chemical kinetic model simulates also the density evolution of the other air plasma species (ions, metastables and atomic and molecular neutral by products of humid air) considering the main collision processes involving charged and neutral particles as ionization, attachment, detachment, dissociation, charge transfer, recombination involving electron-ion, ion-ion and neutral-neutral, etc. This model considering 34 air plasma species and 228 reactions allows to study of the plasma formation and recombination stages during the time scale of the X-ray irradiation. It is first shown that the absorption measurements does not depend on the waveguide frequency in the interval 10 to 16 GHz. We used an irradiation dose of 21.2 Gy in the case of an X-ray pulse having a sin
⁴
time evolution shape with a duration of about 33 ns for full width at half maximum. In this case, the maximum of the measured time resolved electron density is equal to about 4×10
¹³
cm
^-3
. The uncertainty on the electron density using the present absorption method is estimated to about 40%.