Space Plasma Physics The Study of Solar-System Plasmas (1978) / Chapter Skim
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Kenetic Process in the Solar Wind
Kenetic Process in the Solar Wind
Pages 14-53
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From page 14... ...
Kinetic Processes in the Solar Wind William C Feldman University of California, Los Alamos Scientific Laboratory Los Alamos, New Mexico 87545 767
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From page 15... ...
This information, is carried in part by the plasma ions and electrons and is evident in the characteristic shapes of particle velocity distributions at 1 All. It is also evident in the hydromagnetic wave field which consists primarily of large amplitude Alfve"n waves travelling away from the sun in the local solar wind rest frame, A second reason for interest in the solar wind is that it is convenient for studying the state and development of plasma turbulence in an astrophysical setting.
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From page 16... ...
Such information is essential for achieving the stable confinement of fusion plasmas in laboratory devices. For example, the physics of kinetic heat flux regulating mechanisms is only poorly understood, yet is very important for controlling end losses in magnetic confinement devices and for producing spherically symmetric pellet coronae while limiting the preheating of pellet targets in inertially confined devices.
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From page 17... ...
Second a review of longer wavelength fluctuation phenomena of solar origin, which most likely strongly affects the internal state of the solar 14 wind near 1 AU, is covered in an accompanying report, A description of solar wind particle velocity distributions is given first in section 2. This description is followed in sections 3 through 5 by reviews of three of the
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From page 18... ...
' 2) Particle Velocity Distributions in the Solar Wind Near 1 AU a)
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From page 19... ...
In fact recent, more detailed measurements of solar wind electron velocity distributions, indicate a better characterization of fu in terms of a superposition of two separate rl components; a nearly isotropic hot component and a strongly beamed component " 57 travelling away from the sun but along B Although this more complex characterization of fu is only required by two-dimensional measurements such n as shown in Fig.
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From page 20... ...
. Peaks in the electron flux distributions near 1 AIT have been observed as high as 100 kev and as low as 39 ~6 keV, These secondary peaks are generally associated with interplanetary Type III
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b) Protons Proton velocity distributions, f , measured in the solar wind near 1 AU range from isotropic Maxwellian to velocity resolved double streaming 21 configurations.
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3 for two representative proton distributions measured 24 in the high speed solar wind. In the top two panels of Fig.
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From page 23... ...
A thorough knowledge of all possible heat flux regulating mechanisms is therefore essential for understanding the behaviour of physical systems containing hot plasmas, Several processes capable of reducing the flux of heat transported through the solar wind have been suggested as applicable within 1 AU of the sun, Most of these processes are either non kinetic in nature or rely critically on assumed plasma conditions which may or may not apply to the inner solar wind. Since in the interest of brevity, the scope of this report is confined to reviewing only those
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From page 24... ...
It now appears likely that at least one of many possible kinetic heat flux regulating mechanisms is active at times in the solar wind near 1 AU. Solar wind plasma and field data can therefore be used to obtain a detailed and quantitative understanding of this and perhaps other such mechanisms.
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From page 25... ...
Whereas the Alfve"n mode is driven unstable by the relative motion between the cold electrons and the ions, both the magnetosonic and whistler modes are driven unstable by the o o O / relative motion between the hot electrons and the ions. ' The following grossly simplified overview of solar wind heat conduction near 1 Al l can be synthesized from current measurements and ideas as follows.
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From page 26... ...
' In either H case the flow of heat is continuously regulated by the ever decreasing magnitude of the Alfven speed. Because its phase speed is sufficiently high that solar wind ions cannot interact strongly with its oscillating fields, only the heat flux driven whistler mode has been identified tentatively in solar wind data.
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From page 27... ...
The shapes of both electron and ion velocity distributions are generally more complex than those assumed by theoretical analyses of heat flux regulating mechanisms. Since many of these mechanisms involve resonant instabilities which depend sensitively on the shapes of velocity distributions in the resonant velocity range, the physics of heat flux regulation may be considerably more complicated than the simple picture drawn above.
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From page 28... ...
Finally, even if sufficient time is available for the whistler or other instabilities to be effective in limiting AV near 1 AU, a full understanding of heat flux regulation rl requires clarification of the processes which determine the densities and 26 temperatures of f in relation to those of f . It is likely that a basic understanding of the physics of heat conduction in the solar wind requires a fundamentally nonlinear and inhomogeneous theory in which the particle distributions maintain an equilibrium with self-consistent wave fields and continuously adjust to changing plasma conditions as the solar wind convects away from the sun.
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From page 29... ...
It is necessary 1) to understand the plasma mechanism which is responsible for converting the energy carried by an electron beam in a low density plasma into energy carried by plasma oscillations without disrupting the beam and 2)
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From page 30... ...
2. ' ' If true, then plasma waves will be driven unstable in isolated locations in interplanetary space wherever secondary peaks in local electron velocity distributions happen to form.
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From page 31... ...
Even though a complete treatment of proton distribution shapes must include interactions with the entire solar wind wave field independent of origin, for reasons given in section 1 the following discussion concentrates only on kinetic ion beam regulation mechanisms active in the high speed solar wind near 1 ATI. A comprehensive review of other processes which may be effective in determining the internal state of solar wind protons near 1 AU is given 68,43,14 elsewhere.
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From page 32... ...
. An overview of ion beam interactions in the high speed solar wind based on current measurements and ideas is synthesized in the following paragraphs.
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From page 33... ...
Since nonlinear analyses are very difficult, measured solar wind ion velocity distributions have been consulted for guidance. This procedure is expected to provide the desired solutions because as noted earlier, the time required for the solar wind to expand through a density scale height is long compared to typical e-folding growth times of ion-beam driven instabilities.
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From page 34... ...
" The theoretical and experimental proton velocity distributions consist of two interpenetrating beams convecting relative to one another A along the average magnetic field direction, B . The higher density main component travels slower than the nonlinear Alfve"n wave and has a thermal A A speed perpendicular to B which is larger than that parallel to B .
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From page 35... ...
Particular attention is given to He because it is most abundant and should be representative of the heavier ions such as N , 0 and Ne . The evolution of He velocity distributions subsequent to photoionization is not known.
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From page 36... ...
However a subsequent more comprehensive search of solar wind heavy ion spectra yielded only upper limits which were an order of magnitude lower than that expected + 22 if interstellar He ions are quickly thermalized. " Thus although it is possible that occasional solar wind conditions can lead to complete assimilation, most often He velocity distributions must remain diffuse.
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From page 37... ...
7) Summary and Suggested Future Research Velocity distributions of solar wind electrons and ions are observed to be very complex near 1 AU.
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From page 38... ...
2) The heat flux driven whistler instability should be simulated on the
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From page 39... ...
5) High spectral resolution measurements of solar wind ion velocity distributions in conjunction with ion gyroradius and smaller scale wave fields should be extended throughout the inner regions of interplanetary space in order to determine the origin and radial evolution of double ion streams.
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From page 40... ...
7) Detailed measurements in three dimensions should be made of the velocity distributions of as many of the solar wind minor ionic constituents as possible in order to probe the nature of the solar wind wave field.
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From page 41... ...
r -20 -6 HO -5 0 5 10 Electron Velocity (x 10 km/sec) 15 20 FIGURE 1 A cut through a solar wind electron velocity distribution along the magnetic field direction.
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From page 42... ...
H 600 O o UJ 550 > IMP 6 MARCH 19, 1973 500 450 400 TIME (h.UT) 12 FIGURE 4 A plot of the Alfven speed, VA, relative cold component to total electron population bulk speed difference, AVc, and solar wind speed, Vw, during a 12 hour period centered on the maximum speed gradient region at the front edge of a high speed stream.
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From page 43... ...
ECLIPTIC PLANE HIGH DENSITY MAIN COMPONENT LOW DENSITY BEAM COMPONENT FIGURE 6 A schematic 2-dimensional representation of proton velocity distributions measured during high speed solar wind flow conditions. The f direction points radially away from the sun and B0 is the direction of the background magnetic field.
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From page 44... ...
797 Acknow] ed gmen ts I wish to thank B
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From page 45... ...
J Bame, Fast solar electrons, interplanetary plasma and km-wave type III radio bursts observed from the IMP-6 spacecraft, Solar Phys., 44, 485, 1975.
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From page 46... ...
V Goldman, Three-dimensional langmuir wave instabilities in Type III solar radio bursts, Astrophys.
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From page 47... ...
D Montgomery Electron parameter correlations in high speed streams and heat flux instabilities, J
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From page 48... ...
A Gurnett, Direct observations of low-energy solar electrons associated with a type III solar radio burst, Solar Phys., 27, 446, 1972.
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From page 49... ...
R Anderson, Electron plasma oscillations associated with Type III radio bursts, Science, to be publ., 1976.
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From page 50... ...
Fainberg, Simultaneous observations of fast solar electrons and type III radio burst emission near 1 AU, Astrophys. Letters, 14, 191, 1973.
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From page 51... ...
A Smith, Stabilization of electron streams in Type III solar radio bursts, Astrophys.
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From page 52... ...
F., Type III radio bursts and their interpretation, Space Science Rev., l£, 91, 1974.
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From page 53... ...
0, Rapoport, A dynamic theory of type III solar radio bursts, Solar Phys., 24, 444, 1972.
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