Propagation of a nonrelativistic electron beam in a plasma in a magnetic field

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An electron beam was injected into Earth's ionosphere on August 1, 1985, during the flight of the space shuttle Challenger as part of the objectives of the Spacelab 2 mission. In the wake of the space shuttle a magnetically aligned sheet of electrons returning from the direction of propagation of the beam was detected with the free‐flying Plasma Diagnostics Package. The thickness of this sheet of returning electrons was about 20 m. Large intensifications of broadband electrostatic noise were also observed within this sheet of electrons. A numerical simulation of the interaction of the electron beam with the ambient ionospheric plasmas is employed to show that the electron beam excites electron plasma oscillations and that it is possible for the ion acoustic instability to provide a returning flux of hot electrons by means of quasi‐linear diffusion.

Section: Interpretation and Discussionmentioning

confidence: 99%

Electron velocity distributions and plasma waves associated with the injection of an electron beam into the ionosphere

Frank¹,

Paterson²,

Ashour‐Abdalla³

et al. 1989

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“…Note that there is a region in velocity space in which Of/Ov < 0 for V < 0, so that the waves propagating to the negative direction may become unstable in the same way as in the first bin. [Okuda et al, 1987]. Note again that there is a region in velocity space where Of/O• < 0 for V < 0, so that these electron distributions can drive the ion waves unstable via waveparticle interaction.…”

Section: Using the One-dimensional Simulation Model Developed Earliermentioning

confidence: 95%

“…Here we consider an electron beam injected into a fully ionized ambient plasma along the magnetic field from a conducting spacecraft. When the beam density is much smaller than the ambient plasma density, beam electrons can propagate freely into the ambient plasma [Okuda et al, 1987]. The charging of the spacecraft remains small, since the return current carried by the ambient electrons, I a, cancels the beam current I o ---e%V o.…”

Section: Introductionmentioning

confidence: 99%

Ion acoustic instabilities excited by injection of an electron beam in space

Okuda¹,

Ashour‐Abdalla²

1988

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It is shown by means of numerical simulations that an injection of a tenuous suprathermal electron beam into a fully ionized plasma from spacecraft can lead to an excitation of ion acoustic waves. The return current carried by the ambient electrons has a drift speed that is much slower than the beam speed, so that these electrons can excite the ion waves via wave‐particle interaction. Numerical simulations confirm the excitation of ion acoustic waves and the acceleration of ions near the spacecraft producing a high‐energy tail.

“…Thus we see that the one-dimensional results are recovered in the limit as rt:/r • approaches zero. The effect of the beam-plasma interaction on the ambient plasma is much less dramatic than in one-dimensional simulations of electron injection [Okuda et al, 1987]. For the present simulation there is only a weak ripple apparent in the ambient electron phase space, and only a very small number of plasma electrons achieve vx velocities greater than ,,-3 Vrc To approach the one-dimensional limit, one must increase the magnetic field strength and/or increase the beam radius so that the gyroradius r L << %.…”

Section: Since the Energy Flow Into The Plasma Is Now Only Onefourth mentioning

confidence: 93%

“…A number of one-dimensional electrostatic simulations have been performed [Katz et al, 1986;Okuda et al, 1987;Winglee and Pritchett, 1987a] in which electrons were injected into a plasma parallel to the magnetic field. These simulations have confirmed for injection into vacuum and low-density plasma the existence of a stagnation point where beam particles come to a halt [Parks et al, 1975] near the source of the beam.…”

Section: Introductionmentioning

confidence: 99%

The plasma environment during particle beam injection into space plasmas: 1. Electron beams

Pritchett¹,

Winglee²

1987

A new isolated‐system, two‐dimensional electrostatic simulation model is used to investigate the plasma environment in the vicinity of a spacecraft during the injection of electron beams. The propagation of the electron beam and the plasma response to the beam injection are found to vary dramatically depending on the ratio of the ambient plasma density to the beam density. When the ambient plasma density is low, most of the beam electrons are drawn back into the spacecraft by the electric field associated with the charging of the spacecraft. Return currents are associated with field‐aligned flow of the ambient electrons and result in regions of charge imbalance away from the spacecraft. The resulting space‐charge fields produce strong perpendicular heating of the ions on a time scale of the ion plasma period, resulting in conical distributions. As the ambient plasma density is increased, the response time of the plasma to the electric fields associated with the beam injection is decreased. The beam is then increasingly neutralized, and the interaction of the beam with the spacecraft is correspondingly reduced. The fraction of the beam particles that propagate away from the vicinity of the spacecraft is increased. When the ambient plasma density is much larger than the beam density, the beam is able to propagate freely into the plasma. Coherent wave structures are produced in the beam near the spacecraft, while further downstream the beam becomes increasingly turbulent.