A Numerical Investigation on the Behavior of Electrons in the Bullet in the Atmospheric- Pressure Argon Plasma Jet

Electrons are generated abundantly in the plasma jet and play an active role in the mass transfer of reactive species in the aqueous solution in plasma medicine. Such an importance requires knowledge of the behavior of electrons in the plasma jet. The objective of this work is to understand the electron behaviors in the bullet in the plasma jet, including the angle spectrum of electrons (ASEs) and the related energy spectrum, so as to have an insight into those electrons which most probably interact with the target. The numerical modeling based on a needle-plate discharge configuration in conjunction with a 1-D Particle-in-Cell Monte-Carlo Collision (PIC-MCC) simulation method was used to achieve this task. The scattering angle of electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The ASE in the bullet is close to a sinusoidal distribution. As the bullet propagates, the temporal evolution of ASE indicates that relatively more electrons in the bullet are scattered into the angle range below 90°, but at any moment when the propagating bullet is close to the target, ASE in the bullet generally remains unchanged. In addition, relatively less electrons in the bullet are scattered into the angle range below 90° due to the increase of the applied voltage amplitude. For the considered voltage amplitudes below 7 kV, the number of electrons in the angle range below 90° is within 47% of electrons in the bullet and, in these electrons, the proportion of non-subionization electrons reaches about 12%. These results may be taken into consideration in investigating the mass transfer of reactive species in plasma medicine.