Many-particle charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. The author emphasizes the development of PIC computer experiments since the 1950s starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. Details are provided for adding the collisions between the charged particles and neutral atoms. The result is many-particle simulations with many of the features met in low-temperature collision plasmas; for example, with applications to plasma-assisted materials processing, but also related to warmer plasmas at the edges of magnetized fusion plasmas. >

Particle-in-Cell Charged Particle Simulations, plus Monte Carlo Collisions with Neutral Atoms, PIC-MCC

This review presents the basics of plasma discharges applied to electric spacecraft propulsion. It briefly reports on the mature and flown technologies of gridded ion thrusters and Hall thrusters before exploring the recent yet immature technology of plasma thrusters based on expansion from low pressure high density inductively coupled and wave-excited plasma sources, e.g. the radiofrequency helicon source. Prototype development of plasma engines for future space travel is discussed using the example of the helicon double layer thruster. A summary of highlights in electric propulsion based space missions gives some insight into the challenges of future high power missions in more remote regions of space.

/pdf/plasmas-for-spacecraft-propulsion-4uknp98tfc.pdf

Plasmas for spacecraft propulsion

Electrodeless radiofrequency discharges exhibit two modes of operation: a low-density mode in which the power is capacitively coupled to the plasma and which is known as the E-mode, and a higher density mode which is an inductive discharge known as the H-mode. The transition between these modes exhibits hysteresis, i.e. the E to H transition occurs at a different coil current than the reverse H to E transition. Recent theoretical results show that the hysteresis can be qualitatively understood in terms of electron power balance assuming that either the power dissipated or the power absorbed by the plasma electrons has a nonlinear dependence on the electron density. Experiments have been carried out to examine this hypothesis, both by characterizing steady-state E- and H-mode plasmas with a Langmuir probe, and by using a new approach consisting of measuring the internal plasma parameters in a pulsed discharge. In the latter case, the power is time modulated with increasing and decreasing power ramps. This approach allows us to investigate the hysteresis in detail and to study the dynamics of the transition. A number of time-resolved diagnostics including Langmuir probes, current and voltage sensors, optical emission and B-dot probes have been used.

http://iopscience.iop.org/article/10.1088/0963-0252/8/4/309/pdf

Characterization of the E to H transition in a pulsed inductively coupled plasma discharge with internal coil geometry: bi-stability and hysteresis

The behavior of a rapidly pulsed radio-frequency capacitively coupled parallel plate reactor has been investigated using time-resolved voltage probe, microwave interferometer, and optical emission techniques The reactor was operated with 50 mTorr of argon and 100 W rf power (measured at the generator) at 1356 MHz supplied to the 100-mm-diam powered electrode, with pulse durations of 25 and 100 μs For low repetition rates (50 Hz) the voltage envelope has a characteristic form which has been entitled the “Bird’s Head” There is no plasma present at the beginning of the pulse, so that an initial breakdown phase occurs This phase lasts about 600 ns, after which time the plasma density is sufficiently high for the Debye length to enter the gap between the electrodes and for sheaths to form on the electrodes In asymmetric parallel plate reactors the blocking capacitor in the matching circuit charges such that the powered electrode acquires a continuous negative voltage offset (the so-called dc bias) In th

/pdf/the-transition-from-symmetric-to-asymmetric-discharges-in-2pmj8vrew8.pdf

The transition from symmetric to asymmetric discharges in pulsed 13.56 MHz capacitively coupled plasmas

With an implicit particle-in-cell/Monte Carlo model, capacitively coupled plasmas are studied in two-dimensional and axisymmetric geometry. Self-bias dc voltage effects are self-consistently considered. Due to finite length effects, the self-bias dc voltages show complex relations to the electrode areas. Two-dimensional kinetic effects are also illuminated. Compared with the fluid model, PIC/MC model is numerical-diffusion-free and more detailed properties of the plasmas can be shown.

http://iopscience.iop.org/article/10.1088/0963-0252/20/3/035013/pdf

Implicit and electrostatic particle-in-cell/Monte Carlo model in two-dimensional and axisymmetric geometry: II. Self-bias voltage effects in capacitively coupled plasmas

A one dimensional (1D) particle-in-cell (PIC) computer simulation has been used in conjunction with a small experimental plasma reactor, to investigate the effects of pulsing on a low pressure, capacitively coupled, rf argon plasma. In particular this article investigates the time-constants involved in the development and evolution of the bias voltage in asymmetric reactor geometry. Surprisingly, the charging time for the blocking capacitor does not occur on electron time scales, but is influenced primarily by the ambipolar drift of ions to the earthed electrode. It is shown that following plasma breakdown there is a net current flow in the system which charges the blocking capacitor in the external matching circuit and produces the bias voltage. Both the PIC simulation and the experimental measurements show that a net current flow is produced by a delay in the onset of the electron current to the earthed electrode, which is correlated to the charging time of the capacitor. From the simulation it can be s...

/pdf/bias-formation-in-a-pulsed-radiofrequency-argon-discharge-34ws910byf.pdf

Bias formation in a pulsed radiofrequency argon discharge

A 1D Particle-in-Cell (PIC-MCC) simulation has been used to study the effect of temporal modulation (pulsing) of an rf (13.56 MHz) source voltage on the evolution of an argon plasma. Plasma breakdown occurs during the first on- time of the pulse and analytic expressions for the density evolution during and after breakdown are presented for the single pulse case. The effect of multiple pulsing on the plasma development is then examined and compared with the steady state evolution. Experimental measurements of pulsing in a parallel plate rf system are also presented, which have a high qualitative agreement with the simulation results.

Pulsing a Low Pressure Radiofrequency Discharge

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Bias formation in a pulsed radiofrequency argon discharge

Pulsing a Low Pressure Radiofrequency Discharge