PIC simulation of the electron energy distribution function in a RF magnetized plasma column connected to a tilted electrode.

The simple Maxwellian EEDF (Electron Energy Distribution Function) used in collisional plasmas at thermodynamic equilibrium can be distorted when the plasma is close enough to a RF source especially when electrons are well magnetized. This has been verified in our experimental device Aline. During the experiment, negative floating potentials have been found when a Langmuir probe is magnetically connected to the RF electrode, in both direct and capacitive coupling. Floating potentials as low as -40 to -100 V have been measured while the plasma potential remains positive. The large gap between them can be explained by energetic electron beams accelerated in the RF sheath surrounding the electrode. Such acceleration is known as stochastic heating, which is investigated using PIC (Particle in Cells) simulation to demonstrate the importance of the tilting angle of the electrode with respect to the magnetic field direction in the enhancement of these electron beams. Both measurements and PIC simulations show these beams are much stronger at grazing angle, inducing a bi-Maxwellian EEDF with two characteristic temperatures, the highest value explaining the high negative floating potentials. [ABSTRACT FROM AUTHOR]