Plasma Formation - Boyd

Plasma Formation - Boyd - Phys 761 Making and sustaining a...

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Phys 761 “Making and sustaining a Plasma” 9 November 2010 Prof. Derek Boyd We function in a relatively low temperature and high density environment so most of the matter around us is in a molecular state. To make a plasma and sustain it we need to ionize the material and to keep it from reverting back to the molecular state. To do this at liquid or solid densities requires very large power inputs to the material we want to make into a plasma. You can do it by initiating a nuclear explosion or, in small volumes, by irradiating the material with very high power lasers. It is much easier to make a plasma from a gaseous material as you can lower the density with vacuum pumps and so lower the power requirements. The external electric field that will do the work to ionize the atoms can be produced by an incident charged particle or a photon. To make a plasma we must boost the electrons out of the electrostatic wells in which they are confined in the atoms and get a few of them into a Debye sphere. Some of the atoms in this room are ionized by the radioactive nuclei in the materials around us and incident cosmic rays, but we are not living inside a plasma. The Debye shere has a radius equal to a Debye length. On the diagran is an expression fro calculating the number of particles in a Debye sphere. How much energy do we need for ionization? The diagram shows the energy required to ionize the elements of the periodic table.
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Impact Ionization. Notice the internal structure of the atom. A charged particle collides with an atom, an electron is ejected and the charged particle and the ejected electron depart. Three Body Recombination. The inverse process for impact ionization. In this inverse process, an electron and another charged particle collide with an ion, the electron is capture by the ion and thereby neutralized, and the other charged particle leaves carry off the energy and momentum required by the conservation laws.
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Photo Ionization. Here an incoming photo collides with the atom, is absorbed
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Plasma Formation - Boyd - Phys 761 Making and sustaining a...

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