Theory and simulation of anode spots in low pressure plasmas (original) (raw)

Effect of Additional Cathode Potential on Diffused Plasma Parameters in Presence of Anode Potential

Romanian Journal of Physics

The variation of diffused plasma parameters with cathode bias voltage has been investigated in presence of fixed anode bias voltage in a double plasma device. The anode we have considered is the multi-dipole magnetic cage where discharge is carried out and additional cathode is the separation grid of the device. The plasma in the nearby region is the diffused plasma. The plasma parameters in the main discharge region are almost independent of the cathode voltage, but electron density and plasma potential are highly sensitive to it in the diffuse region. The velocity of the ion beam, which is supposed to form in the current configuration of the device, varies inversely to the thickness of the ion sheath formed at the cathode.

Two-dimensional particle simulation of plasma expansion between plane parallel electrodes

Journal of Applied Physics, 1995

We simulate in two dimensions the expansion of a plasma between biased plane parallel electrodes using the particle-in-ce&method. Such a plasma is frequently created in many experiments by the interaction of a pulsed laser with atomic vapor or gas stream. We describe the motion of the electrons and ions and reproduce the experimentally observed bulk drift of the plasma toward the high potential electrode. ,This is explained in terms of the retrograde movement of the ion sheath bound&y on one side of the plasma accompanied by ambipolar diffusion on the other. We estimate the reduced ion density in the plasma by observing oscillations in the space-charge-limited current. By calculating the plasma decay time constant and ambipolar diffusion coefficient, we note that computer simulation can generate data which is difficult to measure experimentally, and not possible to calculate analytically. 0 1995 American Institute of Physics.

Mass Balance in Near-Cathode Plasma and Initiation of Quick-Moving Cathode Spots

IEEE Transactions on Plasma Science, 1984

The explosive model of a quick-moving cathode spot [2], [31 allows us to describe many experimental facts qualitatively. However, some details of the model need further physical explanation, in particular because of the analysis of the latest experimental data [4]. Estimations given in this paper show it is possible to include in the framework of the explosive model mass balance in the plasma ball and explain the fact of the appearance of a new spot at the periphery of an old one observed in experiments [91, [10].

A model for energetic ion generation in an anode plasma

Physics of Fluids B: Plasma Physics, 1993

Mechanisms for energetic ion generation that could explain the observed ion energies in the anode plasma of a magnetically insulated ion diode [Phys. Rev. A 39, 5842 (1989)], are discussed. It is suggested that strong electric fields that result from large density gradients on few tens of micrometers near the anode cause the ion acceleration. Steady state as well as time-dependent accelerations are examined.

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

Plasma Sources Science and Technology, 2020

Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.

Investigating near-anode plasma layers of very high-pressure arc discharges

Journal of Physics D: Applied Physics, 2009

Numerical and experimental investigation of near-anode layers of very high-pressure arcs in mercury and xenon is reported. The simulation is performed by means of a recently developed numerical model in which the whole of a near-electrode layer is simulated in the framework of a single set of equations without simplifying assumptions such as thermal equilibrium, ionization equilibrium and quasi-neutrality and which was used previously for a simulation of the near-cathode plasma layers. The simulation results support the general understanding of similarities and differences between plasma-cathode and plasma-anode interaction in high-pressure arc discharges established in preceding works. In particular, the anode power input is governed primarily by, and is approximately proportional to, the arc current. In the experiment, the spectral radiance from the electrodes and the near-electrode regions in xenon arcs was recorded. The derived total anode power input and near-anode plasma radiance distribution agree reasonably well with the simulation results.

The working principle of the hollow-anode plasma source

Plasma Sources Science and Technology, 1995

The hollow-anode discharge is a special form of glow discharge. It is shown that a drastically reduced anode area is responsible for a positive anode voltage drop of 30-40 V and an increased anode sheath thickness. This leads to an ignition of a relatively dense plasma in front of the anode hole. Langmuir probe measurements inside a specially designed hollow anode plasma source give an electron density and temperature of n e = 10 9 − 10 11 cm -3 and T e = 1 − 3 eV, respectively (nitrogen, current 100 mA, flow rate 5-50 scc/min). Driven by a pressure gradient, the "anode" plasma is blown through the anode hole and forms a bright plasma jet streaming with supersonic velocity (Mach number 1.2). The plasma stream can be used, for instance, in plasma-assisted deposition of thin films.

Electrical investigation of the interaction of a dense plasma with cold electrodes in air

IEEE Transactions on Plasma Science, 1997

The magnetic blowing of an arc against a third so-called commutation electrode positioned perpendicularly to the discharge axis allowed the investigation of a reproducible interaction of the plasma with this electrode. Cathodic arc spots were ignited on the commutation electrode with a negative-biased voltage and anodic spots with a positive-biased voltage. The delay times of arc spot ignition on cathodes have been measured in atmospheric pressure air for 24 different materials of high purity and for several materials of technical quality. Thereby, these materials were ordered as a function of delay time. The cathodic arc spot ignition can be divided into two different forms, one starting with a diffuse current transfer, and the other one initiated by a constricted ignition. The distribution of these forms depends mainly on the surface structure of the cathodes. A satisfactory explanation of the results can be given by proceeding on the assumption that surface effects are dominant over the bulk properties of the material.

Positive anode sheath with ionization in an arc discharge

Physics of Plasmas, 2020

When the plasma is unable to provide the positive anode sheath with ions (small anode, low anode plasma conductivity, ablating anode), the ions must be generated inside the sheath itself. The Poisson equation for the sheath with ion generation is solved. The ion flux from the sheath to the neutral plasma is obtained as a function of the anode voltage drop. It is shown that in the case of highly intensive ion generation, the mode with monotonous potential ceases to exist. It is hypothesized that a double layer is formed. It is suggested that the analysis could be applicable to the anode layer of a glow discharge.