Numerical study of sheath formation in multi-ion species plasmas

A study of multi-ion species plasmas in divertor region through kinetic simulation helps us understand particle transports and wall interactions. We analyzed plasma sheath behavior without collisions involving electrons, hydrogen isotopes, and helium ions using a one-dimensional spatial space and three-dimensional velocity space (1D3V) Particle-In-Cell (PIC) simulation. The PIC simulation model follows Maxwellian velocity distributions with the pre-sheath acceleration for each particle species in the plasma source, and the plasmas move to the absorption wall with equal and constant flux. This revealed spatial potential variations due to differences in masses and charges of multi-ion species plasmas, including independent sound velocities of each ion species. Increasing ion masses result in a more negative wall potential. The electrostatic force repels electrons and accelerates multi-ions to reach the absorption wall. This information is found in the phase spaces of velocity in the sheath.