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Many times I heared that the solar wind consists of protons and alpha particles. The both are positively charged, but are there electrons in solar wind?

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+1 this is a good discussion to have. From what I understand of plasma physics, the charge balance is maintained fairly strictly throughout all of any plasma. Do some simple calculations assuming complete and total stripping of electrons in even a small amount of matter and you find that the electric potential has comparable energy to a nuclear bomb. Over large scales in space, accumulated electric and magnetic fields can matter a great deal. –  AlanSE Aug 15 '11 at 15:08
could be estimated from what is brighter "Aurora Borealis" or "Aurora Australis"? –  troyaner Aug 15 '11 at 15:09
@troyaner I'm curious, could you elaborate on the "Aurora Borealis" / "Aurora Australis" connection? –  AlanSE Aug 15 '11 at 15:25
my first thought was that protons and electrons travel to different poles (I can be wrong here) –  troyaner Aug 15 '11 at 15:30
@Zassounotsukushi on the other hand it is quite easy to separate alpha and beta rays - you need only a good magnet. –  Anixx Aug 15 '11 at 18:28
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4 Answers

Solar wind is neutral overall else the Sun will become globally very strongly charged and we don't see that happening.

It comprises Electrons/Protons and other particles.

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The reason solar wind protons are so often mentioned is because their mass is almost three orders of magnitude greater than electrons, even though they have equal but opposite charge. –  Michael Luciuk Aug 15 '11 at 14:46
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Generally plasma may be charged in regions smaller than the Debye length. Normally it happens at boundaries. For example, fast electrons tend to fly away and are deposited on a metallic wall first. (It is like electron emission from a hot cathode.) Thus a positive charge is created within some region. The Debye length depends on plasma density and temperature.

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That length is about $10 m$ for the interstellar space, could space travelers see electronic interference due to the voltage fluctuations? –  AlanSE Aug 15 '11 at 19:11
I cannot estimate the voltage right now, unfortunately. It should be compared with the measuring device noise amplitude. –  Vladimir Kalitvianski Aug 15 '11 at 20:36
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The electrons in the solar atmosphere have a lower escape velocity because of their mass. The flux of electrons creates a positive charge in the solar atmosphere that in time creates an ambipolar electric field that then accelerate protons to space. This caused the solar wind to be essentially neutral.

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This is a citation about solar wind properties from:

Hargreaves, J. K. (1995). The solar-terrestrial environment. Cambridge University press

Although most ions are protons ($\mathrm{H}^+$) there is an $\alpha$-particle ($\mathrm{He}^{++}$) component typically amounting to 5% thought exceptionally up to 20% of the total. Heavier atoms total perhaps 0.5%, and, in contrast to the light ions, these are not fully ionized. The number density of positive ions varies between 3 and 10 $\mathrm{cm}^{-3} (3 \times 10^6\;\mathrm{to}\;10^7 \mathrm{m}^{-3})$, the most typical value being 5 $\mathrm{cm}^{-3}$, and there is a similar number of electrons for bulk neutrality.

So the answer (as it was posted before) is NO, the solar wind is overall neutral and YES there are enough electrons to make it so.

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