1 The Equations of Gas Dynamics 2 Magnetoplasma Dynamics 3 Waves in Magnetoplasmas 4 Magnetoplasma Stability 5 Transport in Magnetoplasmas 6 Extensions of Theory Bibliography Index

Physics of plasmas

This paper reviews the most commonly used methods for the generation of plasmas with special emphasis on non-thermal, low-temperature plasmas for technological applications. We also discuss various technical realizations of plasma sources for selected applications. This paper is further limited to the discussion of plasma generation methods that employ electric fields. The various plasmas described include dc glow discharges, either operated continuously (CW) or pulsed, capacitively and inductively coupled rf discharges, helicon discharges, and microwave discharges. Various examples of technical realizations of plasmas in closed structures (cavities), in open structures (surfatron, planar plasma source), and in magnetic fields (electron cyclotron resonance sources) are discussed in detail. Finally, we mention dielectric barrier discharges as convenient sources of non-thermal plasmas at high pressures (up to atmospheric pressure) and beam-produced plasmas. It is the main objective of this paper to give an overview of the wide range of diverse plasma generation methods and plasma sources and highlight the broad spectrum of plasma properties which, in turn, lead to a wide range of diverse technological and technical applications.

https://iopscience.iop.org/article/10.1088/0963-0252/9/4/301/pdf

Plasma generation and plasma sources

The advantages of nuclear fusion as an energy source and research progress in this area are summarized. The current state of the art is described. Laser fusion, inertial confinement fusion, and magnetic fusion (the tokamak) are explained, the latter in some detail. Remaining problems and planned future reactors are considered. They are the Compact Ignition Tokamak (CIT), the International Thermonuclear Experimental Reactor (ITER), and a US design called TIBER II. The design of the latter is shown. >

http://ieeexplore.ieee.org/iel1/45/1370/00031587.pdf

Nuclear fusion

http://ieeexplore.ieee.org/iel5/4639142/31561/01472527.pdf

Controlled fusion

First observed in gaseous plasmas in the early 1960s, helicon discharges lay like a sleeping giant until they emerged in the 1980s, when their usefulness as efficient plasma sources for processing microelectronic circuits for the burgeoning semiconductor industry became recognized. Research on helicons spread to many countries; new, challenging, unexpected problems arose, and these have spawned solutions and novel insights into the physical mechanisms in magnetized radio-frequency discharges. Among the most baffling puzzles were the reason for the high ionization efficiency of helicon discharges and the dominance of the right-hand polarized mode over the left-hand one. The most recent results indicate that a nonobvious resolution of these problems is at hand.

/pdf/helicons-the-past-decade-o5uhc6xlmq.pdf

Helicons-the past decade

Components of the wave magnetic field in a helicon discharge have been measured with a single‐turn, coaxial magnetic probe. Left‐ and right‐handed helical antennas, as well as plane‐polarized antennas, were used; and the results were compared with the field patterns computed for a nonuniform plasma. The results show that the right‐hand circularly polarized mode is preferentially excited with all antennas, even those designed to excite the left‐hand mode. For right‐hand excitation, the radial amplitude profiles are in excellent agreement with computations.

/pdf/helicon-wave-excitation-with-helical-antennas-5ap4fyzv9m.pdf

Helicon wave excitation with helical antennas

Traveling‐ and standing‐wave characteristics of the wave fields have been measured in a helicon discharge using a five‐turn, balanced magnetic probe movable along the discharge axis z. Helical and plane‐polarized antennas were used, and the magnitude and direction of the static magnetic field were varied, yielding three primary results. (1) As the density varies along z, the local wavelength agrees with the local dispersion relation. (2) Beats in the z variation of the wave intensity do not indicate standing waves, but instead are caused by the simultaneous excitation of two radial eigenmodes. Quantitative agreement with theory is obtained. (3) The damping rate of the helicon wave is consistent with theoretical predictions based on collisions alone.

/pdf/axial-propagation-of-helicon-waves-1yjo9s04po.pdf

Axial propagation of helicon waves

Measurements of the radial and axial profiles of both the plasma parameters and the wave properties in a long, thin helicon discharge show that most of the RF power is deposited near the antenna and that a dense, cool ( eV) plasma can be obtained in the downstream region. The density n and electron temperature profiles in that region can be explained quantitatively with classical collisional theory, and factor-of-two agreement can be obtained on total particle and energy balance. Spatial modulation of the helicon wave amplitude can be explained by the beating of two different radial modes launched simultaneously by the antenna. Though the helicon wave can be shown to be essential to the production of high densities, it plays little role in the downstream evolution of the plasma. These results indicate that helicon discharges can produce the cool plasmas normally associated with afterglows without the attendant loss of density.

/pdf/downstream-physics-of-the-helicon-discharge-2zx2vehq3f.pdf

Downstream physics of the helicon discharge

Recent discoveries in a helicon plasma show a decrease in equilibrium plasma density as magnetic field strength is increased. This can be explained in the framework of a low frequency electrostatic instability. However, quiescent plasma behavior in helicon sources has been hitherto accepted. To verify the existence of an instability, extensive measurements of fluctuating quantities and losses as a function of magnetic field were implemented. Furthermore, a theoretical model was developed to compare to the measurements. Theory and measurement show very good agreement; both verifying the existence of a low frequency instability and showing that it is indeed responsible for the observed density characteristic.

/pdf/low-frequency-electrostatic-instability-in-a-helicon-plasma-5e8rtqynr7.pdf

Low frequency electrostatic instability in a helicon plasma

The dispersion relation for helicon waves in a cold plasma of radially varying density has been reduced to compact form, and the radial eigenmodes have been computed for different density profiles The results show a marked asymmetry between the left- and right-hand circularly polarized modes: the m=-1 (left) mode has a centrally peaked wave intensity and resonates with a much higher central density than the m=+1 mode Positive feedback is therefore possible, leading to nonlinear channelling of the discharge At a radius where the density falls to a certain value, a singularity arises in the coefficients of the wave equation; care must be taken in integrating through this point This singularity has no physical significance The marked difference between the m=+1 and -1 modes in a non-uniform plasma is caused by a difference in sign of the electron drift along the density gradient Energy deposition is peaked near the radius of the peak in Bz, so that broad, uniform density profiles can be obtained by using the m=+1 mode and narrow, dense columns by using the m=-1 mode These results explain many features observed by various groups over the past two years

Max Light

Papers

Helicon wave excitation with helical antennas

Axial propagation of helicon waves

Downstream physics of the helicon discharge

Low frequency electrostatic instability in a helicon plasma

Helicon waves in a non-uniform plasma