Termination of a Magnetized Plasma on a Neutral Gas: The End of the Plasma

In this paper it is shown that a stationary plasma can be accelerated by a moving neutral gas only if the velocity of the neutral gas exceeds Alfvén's critical velocity. An expression for the terminal velocity of the interaction is given which shows that, in the limit of high incoming neutral gas speeds, the composite plasma is accelerated up to one quarter of the gas speed. We also discuss terminal velocities associated with the inverse problem, namely the deceleration of a magnetized plasma as a result of its motion through, and interaction with, a stationary neutral gas.

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On Alfv�n's critical velocity for the interaction of a neutral gas with a moving magnetized plasma

Astrophysics and Space Science ◽

10.1007/bf00642583 ◽

1978 ◽

Vol 55 (1) ◽

pp. 113-124 ◽

Cited By ~ 18

Author(s):

R. K. Varma

Keyword(s):

Critical Velocity ◽

Magnetized Plasma ◽

Neutral Gas

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The Effect of Ionization and Recombination on the Resistivity of a Partially Ionized Plasma in a Magnetic Field

Australian Journal of Physics ◽

10.1071/ph780171 ◽

1978 ◽

Vol 31 (2) ◽

pp. 171 ◽

Cited By ~ 5

Author(s):

CD Mathers ◽

NF Cramer

Keyword(s):

Magnetic Field ◽

Major Effect ◽

Magnetized Plasma ◽

Neutral Atoms ◽

Laboratory Conditions ◽

Electron Atom ◽

Neutral Gas ◽

Partially Ionized ◽

Three Body ◽

The Magnetic Field

The generalized Ohm's law for a partially ionized magnetized plasma composed of ions, electrons and neutral atoms is calculated. The plasma is modelled by a three-fluid treatment, with elastic collisions between all three species, as well as inelastic ionization and recombination collisions being taken into account. Ionization is assumed to be due to electron-atom impacts, and recombination is assumed to be due to three-body electron-electron-atom collisions. The resistivity is calculated, and it is shown that the major effect of ionization and recombination is to reduce the resistivity for currents perpendicular to the magnetic field under typical laboratory conditions. However, this resistivity is still greater than Coulomb resistivity, owing to plasma-neutral gas friction.

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On the threshold velocity in the interaction between a magnetized plasma and a neutral gas

Physics Letters A ◽

10.1016/0375-9601(80)90485-5 ◽

1980 ◽

Vol 76 (3-4) ◽

pp. 257-260 ◽

Cited By ~ 14

Author(s):

S.K. Mattoo ◽

N. Venkataramani

Keyword(s):

Magnetized Plasma ◽

Threshold Velocity ◽

Neutral Gas

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Cross-field diffusion quenching by neutral gas injection in a magnetized plasma

Physical Review Letters ◽

10.1103/physrevlett.68.2925 ◽

1992 ◽

Vol 68 (19) ◽

pp. 2925-2928 ◽

Cited By ~ 13

Author(s):

A. Fasoli ◽

F. Skiff ◽

T. N. Good ◽

P. J. Paris

Keyword(s):

Gas Injection ◽

Magnetized Plasma ◽

Neutral Gas ◽

Field Diffusion

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Shock waves in gas and plasma

Laser and Particle Beams ◽

10.1017/s0263034600009885 ◽

1996 ◽

Vol 14 (2) ◽

pp. 125-132 ◽

Cited By ~ 6

Author(s):

K. Niu

Keyword(s):

Magnetic Field ◽

Shock Wave ◽

Inertial Confinement Fusion ◽

Magnetized Plasma ◽

Irreversible Processes ◽

Wave Flow ◽

Discontinuous Surface ◽

Neutral Gas ◽

The Magnetic Field ◽

Free Shock

A shock wave is a discontinuous surface that connects supersonic flow with subsonic flow. After a shock wave, flow velocity is reduced, and pressure and temperature increase; entropy especially increases across a shock wave. Therefore, flow is in nonequilibrium, and irreversible processes occur inside the shock layer. The thickness of a shock wave in neutral gas is of the order of the mean free path of the fluid particle. A shock wave also appears in magnetized plasma. Provided that when the plasma flow is parallel to the magnetic field, a shock wave appears if the governing equation for velocity potential is in hyperbolic type in relation with the Mach number and the Alfvén number. When the flow is perpendicular to the magnetic field, the Maxwell stress, in addition to the pressure, plays a role in the shock wave in plasma. When the plasma temperature is so high, as the plasma becomes collision-free, another type of shock wave appears. In a collision-free shock wave, gyromotions of electrons around the magnetic field lines cause the shock formation instead of collisions in a collision-dominant plasma or neutral gas. Regardless of a collision-dominant or collision-free shock wave, the fluid that passes through the shock wave is heated in addition to being compressed. In inertial confinement fusion, the fuel must be compressed. Really, implosion motion performs fuel compression. A shock wave, appearing in the process of implosion, compresses the fuel. The shock wave, however, heats the fuel more intensively, and it makes it difficult to compress the fuel further because high temperatures invite high pressure. Adiabatic compression of the fuel is the desired result during the implosion, without the formation of a shock wave.

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Sheaths and Double Layers with Instabilities

Journal of Technological and Space Plasmas ◽

10.31281/jtsp.v2i1.16 ◽

2021 ◽

Vol 2 (1) ◽

pp. 70-92

Author(s):

Reiner L Stenzel ◽

Johannes Grünwald ◽

Codrina Ionita ◽

Roman Schrittwieser ◽

Manuel Urrutia

Keyword(s):

Double Layer ◽

Secondary Electron Emission ◽

Low Frequency ◽

Negative Electrode ◽

Density Perturbation ◽

Magnetized Plasma ◽

Double Layers ◽

Electrode Current ◽

Neutral Gas ◽

The Impact

The properties of sheaths and associated potential structures and instabilities cover a broad field which even a review cannot cover everything. Thus, the focus will be on about a dozen examples, describe their observations and focus on the basic physical explanations for the effects, while further details are found in the references. Due to familiarity the review focuses mainly on the authors work but compared and referenced related work. The topics start with a high frequency oscillations near the electron plasma frequency. Low frequency instabilities also occur at the ion plasma frequency.The injection of ions into an electron-rich sheath widens the sheath and forms a double layer. Likewise, the injection of electrons into an ion rich sheath widens and establishes a double layer which occurs in free plasma injection into vacuum. The sheath widens and forms a double layer by ionization in an electron rich sheath. When particle fluxes in "fireballs" gets out of balance the double layer performs relaxation instabilities which has been studied extensively. Fireballs inside spherical electrodes create a new instability due to the transit time of trapped electrons. On cylindrical and spherical electrodes the electron rich sheath rotates in magnetized plasmas. Electrons rotate due to $\mathbf E \times \mathbf B_0$ which excites electron drift waves with azimuthal eigenmodes. Conversely a permanent magnetic dipole has been used as a negative electrode. The impact of energetic ions produces secondary electron emission, forming a ring of plasma around the magnetic equator. Such "magnetrons" are subject to various instabilities. Finally, the current to a positively biased electrode in a uniformly magnetized plasma is unstable to relaxation oscillations, which shows an example of global effects. The sheath at the electrode raises the potential in the flux tube of the electrode thereby creating a radial sheath which moves unmagnetized ions radially. The ion motion creates a density perturbation which affects the electrode current. If the electrode draws large currents the current disruptions create large inductive voltages on the electrode, which again produce double layers. This phenomenon has been seen in reconnection currents. Many examples of sheath properties will be explained. Although the focus is on the physics some examples of applications will be suggested such as neutral gas heating and accelerating, sputtering of plasma magnetrons and rf oscillators.

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