404 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



circle, a radial force is applied, and in conserving its angular momen- 

 tum the particle speeds up so that it not only moves in tighter spirals 

 but goes aromid the tighter spirals more raf)idly. In the Van Allen 

 belts, the plasma particles are caught in a gigantic "magnetic mirror." 

 As these ions and electrons approach the poles, they are womid in 

 tighter spirals, but as they rotate faster in smaller circles they con- 

 serve energy by moving more slowly toward the poles. In fact, they 

 actually slow down and stop, and are then reflected by the mirror into 

 reversing their directions. They go back and forth, caught in the 

 Van Allen belts. The mirror effect is not perfect, and the charged 

 particles leaking out the ends of the Van Allen belts cause the north- 

 ern lights, or the aurora borealis. This electrical discharge is the 

 visible mdication of the ionosphere, or the charged plasma, escaping 

 out the ends of the Van Allen belts. 



Our very existence on earth depends upon our greatest plasma 

 source, the smi. Its energy comes from the process we call thermonu- 

 clear fusion. Two heavy hydrogen nuclei are fused in such a way 

 that helium is formed. There is energy left over wliich keeps the 

 process going and incidentally keeps us warm. The whole process 

 of the o]3eration of the sun is a nuclear reaction occuring in the plasma 

 of the sun itself. 



There are some other things on the diagi'am that show how univer- 

 sal the plasma state is. Perhaps one of the earliest plasmas studied 

 as an easy way of producing a neutral collection of electrons and ions 

 was a flame. A flame even from a candle is not very hot, maybe 1,000 

 degrees K, but it is extremely dense because it occurs at atmospheric 

 pressure. Chemical flames themselves are not usually studied, but 

 many varieties of chemical or electric "torches" produce plasmas 

 which are not only laboratory tools for increasing our understanding 

 of the plasma state but are technically important tools for such varied 

 operations as welding or chemical synthesis. Also, for example, me- 

 teors burn up when they come into the atmosphere and are reduced 

 to the plasma state. Much of our information about meteoric physics 

 and chemistry comes from studies of the behavior of the plasma state. 



If you go to a plasma a little hotter than a flame, and a little denser, 

 you come to the most common everyday form of plasma, a gas dis- 

 charge tube of some sort, a neon sign or a fluorescent light. Most of 

 the original studies of the plasma state were done in what was called 

 a "glow discharge" because this was a readily available way of pro- 

 ducing a plasma to study in the laboratory. A great deal of the infor- 

 mation we are now gaining about the ionosphere, the sun, and 

 interplanetary and interstellar space comes from studies made in the 

 laboratory with a glow discharge. Practically, there are many appli- 

 cations of a glow discharge, particularly in the field of control and 

 gas tubes of various sorts. Glow discharge studies not only explore 



