9 research outputs found
A fluid model of the current-voltage characteristics of an electron emitting electrode immersed in a two electron temperature plasma
The current voltage characteristics of a negatively biased
electron emitting electrode immersed in a two-electron temperature
plasma are analyzed by a simple one dimensional fluid model. Based
on the assumption that the electron density in the pre-sheath
region obeys the Boltzmann law the Bohm criterion is derived in
the form of a transcendental equation for the Mach number, which
can have up to 3Ā solutions. According to these solutions the ion
velocity at the sheath edge can be determined either by the hot or
by the cool electron temperature. When it is determined by the
cool electron temperature and the hot electron temperature is high
enough the critical electron emission current from the collector
can have a very pronounced local maximum and a minimum when
regarded as a function of the electrode potential. Because of that
the current voltage characteristics of the electrode may exhibit
up to 3Ā different floating potentials. This result is in good
agreement with the experimental observations reported in [J. Appl. Phys. 63, 5674 (1988)]
Pre-sheath formation in an oblique magnetic field: fluid model and PIC simulation
We present some results of a one-dimensional fluid model with a floating electrode immersed in plasma with magnetic field applied at an oblique angle. The model equations are integrated numerically in order to find the space profiles of the ion velocities and electrostatic potential for various strenghts and angles of the magnetic field. We assume a collisionless magnetized pre-sheath with isothermal ions. The results are then compared with the spatial profiles obtained by a computer simulation. We use a BIT1 particle-in-cell code. The simulations input parameters are chosen in the way, that they resemble the fluid model as much as possible. Because the results of the simulation are given in the absolute SI units, they have to be normalized correctly. We evaluate the model results and compare them with the computer simulation results. Special attention is brought on formation of the pre-sheath with magnetic field applied at intermediate angles. The results of the simulation are in good qualitative agreement with the model