#13. Energetic ParticlesThe atoms and molecules of a gas are in constant motion, colliding rapidly and filling all available space. The hotter the gas, the faster they move, and the more energy each of them holds. The free ions and electrons in a plasma behave the same way.
Knowing the temperature of the high atmosphere of Earth, or that of the Sun, we can calculate energies expected of ions and electrons found there. However, ions and electrons actually observed in space are often much, much more energetic, and may move at a respectable fraction of the velocity of light (300,000 km/sec or 186,000 miles/sec). One guesses that they get energized by electric and magnetic processes, not just by mere heat.
As described in the section on the electron, suppose that in a vacuum electrons come out of a hot slab A (drawing below), heated by a separate wire so that the voltage of the heating coil is not part of the circuit. Then if these electrons are attracted to a second plate B with a voltage (relative to A ) of +1 volt, each electron gains one electron volt. If the voltage is 10 volts, it gains ten times as much or 10 ev, a bit like a stone dropped from a height 10 times larger.|
In the picture tube of a color TV, electrons are accelerated by about 30,000 volts, so that their energy when they hit the screen is about 30,000 ev. That is actually quite a lot: those electrons move at about 1/3 the velocity of light. But then, a TV picture tube is a quite sophisticated instrument. In a doctor's x-ray machine electrons are accelerated to energies 2-3 times higher, after which they hit a target and produce a spray of x-rays.|
Particle Energies in Nature
How does nature compare?
We need bigger units:
Note on RelativityThe theory of relativity allows no particle with mass to move as fast as light, but there is no limit on its energy. Close to the speed of light, however, the addition of energy only slightly increases the velocity. An ion accelerating from 0.9 to 0.99 times the speed of light needs several times more energy than the amount it needed to reach 0.9 times in the first place.
Why and HowWhere do single electrons and ions acquire such high energies? Excellent question. We guess magnetic and electric fields may be involved, and have learned a great deal in that direction, but the exact processes (probably more than one) remain to be nailed down. Acceleration takes place in solar flares and CMEs (see Sun) but, like a clever conjuring trick, although it happens right in front of our eyes, we still don't get it.
Our best chance may be to study the acceleration of particles in the aurora and radiation belt to more moderate energies, since it occurs in a region of space which instrumented satellites can probe. As we study such acceleration processes we gradually learn how plasmas and magnetic fields interact in space, and that experience can then be applied to the rest of the universe.
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Last updated: December 31, 1998