Monte Carlo Collision Simulation Research Articles

Three-Dimensional Numerical Simulation of Field-Emission-Electric-Propulsion Backflow Contamination

A three-dimensional full particle particle-in-cell with Monte Carlo collision simulation model is developed to study charge-exchange ion backe ow from a e eld-emission-electric-propulsion thruster using liquid cesium as a propellant. Contamination from backe ow of low-energy charge-exchange ions generated in the plume is an important spacecraft integration issue. Simulations show that the backe ow ion current is on the order of 0.01% of the total emitting current under typical thruster operating conditions. Nearly all charge-exchange ions are collected by the accelerator electrode close to the emitter. Operating a e eld emission thruster at lower neutral e ux, lower emitter current, or higher emitter potentials helps to reduce the backe ow current and possible spacecraft contamination. The operation of a neutralizer does not have a signie cant effect on the backe ow current under typical space plasma environments. A semi-analytical expression is also derived for quick estimations of the e eld emission thruster backe ow current. Nomenclature Aacc = accelerator area, m 2 Ae; Ai; An = exit area of the electron, ion, and neutral beam, m 2 a = emitter‐accelerator distance, m b = half of accelerator aperature, m C

Electrical characterization of an rf planar magnetron in inertgases

Electrical aspects of an rf planar magnetron discharge in noblegases at pressures below 50 mTorr are discussed. The electrical parametersof the experimental device are measured by a diagnostic system consistingof two probes, a capacitive voltage divider and a current loop. Themeasurements of the rf current and voltage and the fast Fourier transformtreatment of recorded signals are used to verify the validity of the`subtraction' method in order to estimate the power deposited into theplasma. This technique shows a better power coupling with a metallictarget, up to 90% of the rf delivered power, than for an insulatingtarget for which the power efficiency hardly reaches 50%. In addition,the elementary mechanisms sustaining the rf planar magnetron discharge areanalysed. A transition from a combination of α (`wave-riding') andγ (secondary electron emission) regimes above a critical pressureto an α dominant regime at very low pressure is pointed out. Thisphenomenon is explained by the results of a particle-in-cell Monte Carlocollision simulation.

Fast approach to kinetic simulations of RF discharge in plasma reactors

A calculational approach is developed to accelerate the particle-in-cell Monte Carlo-collision simulations of a radio-frequency discharge plasma. It is based on the splitting of the treatment of fast-relaxing and slow-relaxing distribution functions, which allows one to avoid some time-step limitations. Comparisons with the usual simulation method shows a 10 to 30 times decrease of computational expenses.

Monte Carlo Collision Simulation of Positive-Negative Ion Recombination for a Given Rate Constant

Here is proposed the Monte Carlo collision simulation method for the positive-negative ion recombination whose rate constant is given as a function of temperature. The method makes it possible to simulate a nonequilibrium state of ions in electric discharges.

Three-dimensional electromagnetic particle-in-cell with Monte Carlo collision simulations on three MIMD parallel computers

A three-dimensional electromagnetic particle-in-cell code with Monte Carlo collision (PIC-MCC) is developed for MIMD parallel supercomputers. This code uses a standard relativistic leapfrog scheme incorporating Monte Carlo calculations to push plasma particles and to include collisional effects on particle orbits. A local finite-difference time-domain method is used to update the self-consistent electromagnetic fields. The code is implemented using the General Concurrent PIC (GCPIC) algorithm, which uses domain decomposition to divide the computation among the processors. Particles must be exchanged between processors as they move among subdomains. Message passing is implemented using the Express Cubix library and the PVM. We evaluate the performance of this code using a 512-processor Intel Touchstone Delta, a 512-processor Intel Paragon, and a 256-processor CRAY T3D. It is shown that a high parallel efficiency exceeding 95% has been achieved on all three machines for large problems. We have run PIC-MCC simulations using several hundred million particles with several million collisions per time step. For these large-scale simulations the particle push time achieved is in the range of 90–115 ns/particle/time step, and the collision calculation time in the range of a few hundred nanoseconds per collision.

Electron energy dynamics in a RF discharge with trapezoidal driving voltage: comparison of experiment and particle-in-cell Monte Carlo collision simulation

We report on the properties of a special RF discharge characterized by a trapezoidal shape of the driving voltage pulse. This driving mode offers an advantage in comparison to the common sinusoidal voltage - in allowing the separation in time of effects which are connected with the time derivative of the driving voltage (displacement current, -mechanism) from effects connected with the amplitude of the driving voltage (production of electrons at the electrodes, -mechanism). The energy gain and loss of electrons in this RF discharge are studied in a collision-dominated helium discharge with special emphasis on the -mechanism. Experimental results of space- and time-resolved plasma-induced emission spectroscopy are compared and combined with the results of a particle-in-cell Monte Carlo collision simulation. It is demonstrated that the electrons gain energy during the temporal change of the discharge voltage at high neutral particle pressure (400 Pa) in the vicinity of both sheaths and that they dissipate energy in these regions by inelastic collisions. At a lower neutral particle pressure (100 Pa) the electrons gain energy in the vicinity of the expanding sheath and lose energy at the contracting sheath. In this case the energy loss by inelastic collisions takes place in the bulk plasma.