Generation of energetic electrons in pulsed microwave plasmas

Pulsed microwave driven microplasma at atmospheric pressure is proposed as an efficient source of energetic electrons for low-temperature biomedical applications. Energetic electrons are required to break the covalent bonds of nitrogen, oxygen, and water molecules in humid air and produce reactive species. Particle-in-cell (PIC) simulations demonstrate that the energetic electrons with energy greater than 10eV (capable of breaking the bond of nitrogen molecules) can be produced much more efficiently in pulsed microwave helium plasmas than in pulsed DC or continuous microwave plasmas. In particular, fast heating and cooling of electrons are observed at the rising edge and the falling edge of the pulse, respectively. This phenomenon is consistent with the fluid analysis showing the electrons' energy gain via collective motion and collisional loss to the neutral particles.