Ion energy distributions to particles in RF and corona discharges

Summary form only given. Ion energy and angular distributions (IEADs) to particles suspended in plasmas is of interest from many perspectives. In low pressure plasmas, ion drag forces are important to the particles´ transport and depend on the IEADs, as do particle heating rates. In atmospheric pressure plasmas, particles may be of the form of bacteria, and so the energy delivered by the IEADs in part determines the plasma´s sterilization capability. In this talk we report on results from a computational investigation of IEADs incident on particles. The model used in this work, nonPDPSIM, is a plasma hydrodynamics model in which continuity, momentum and energy equations are solved for charged species with solution of Poisson´s equation [1]. An unstructured mesh having a dynamic range of >1000 is used to enable both the reactor scale and the particles (many to tens of microns in size) to be resolved in a single mesh. To compute IEADs to the particle surface a Monte Carlo simulation is used to advance trajectories of pseudo-particles in time-varying electric fields while accounting for elastic and inelastic collisions. IEADs to particles in two classes of discharges will be discussed; a low pressure (tens to hundreds mTorr) rf discharge, and atmospheric pressure positive and negative streamers. For low pressure rf discharges the directionality of the IEAD incident onto the particle is in large part determined by the position of the particle in the sheath. This directional component in part determines the ion drag force. In the atmospheric pressure discharge, streamers intersecting the particle momentarily generate a large sheath potential as the streamer passes. At that time, ions of energies up to 20 eV can strike the particle. The shape, size and permittivity of the particle in part determine the character of the IEAD.