Investigations of a virtual cathode under complex conditions using grid-free treecode method

Summary form only given. A treecode numerical method was first introduced by Barnes and Hut in astrophysics [Barnes, J., et al., 1986] for simulation of many-body particle systems interacting in a gravitational field. Main advantage of this newly developing method is that it is grid-free, i.e. there is no need to define a grid in advance. This means that during a simulation of the motion of particles in external field, particles are grouped in clusters based on some well advanced criteria, e.g., the particle local number density. First attempt to develop a treecode method for a bounded plasma has been done by Christlieb, Krasny and Verboncoeur [Christlieb, A.J., et al., 2004] with the application to the particle dynamics in a diode with a single mono-energetic particles. In a previous work of Krek et al. [Krek, J., et al., 2011] the treecode method code was upgraded for more than a one kind of mono-energetic species and effects of imbalance of particle densities to the diode behavior was investigated. In the present work we proceed with investigations of plasma diode under more complex conditions (both volume particle generation and surface particle injection with finite arbitrary temperatures of Maxwellian distributed particles). Here we present the effects of these new parameters to the diode behavior using treecode method with these new incorporated features in comparison with the results obtained using Particle-In-Cell (PIC method [Birdsal, C.K., et al., 1985]) and discuss both physical results and computational advantages and disadvantages of treecode method.