Science and Public Policy: National Security 115 



or far infrared region as has been found by Kittel, Buchsbaum, 

 Hebel, Boyle, Wolff and others. Obviously a great variety of 

 plasmas can occur in solids, in contrast to the rather conven- 

 tional gas plasma of electrons and ions in which both com- 

 ponents are mobile. For instance, in an intrinsic semiconductor, 

 where at ordinary temperatures electrons and holes are present 

 in equal numbers, we can have there a two-component plasma 

 (Fig. II). In the metal potassium, however, there is a sea of 

 conduction electrons with fixed K+ ions, so there is a single 

 mobile component (Fig. 12). Generally in a solid the behavior 

 of conduction electrons is set, of course, by the periodic crystal 

 field, and each solid may be somewhat different in this respect, 

 so the range of electron dynamics for solid plasma is almost as 

 great as the range of kinds of conducting solids themselves. The 

 effective masses of these plasma particles also may vary from 



WHEN W«Wc 

 Bo Bo 



Ne ^N^ Ng = Nh 



Figure 11.— Mechanism determining plasma frequencies when 



