Radiative Processes in Discharge Plasmas: Questions and Issues
When a gas is heated to a sufficiently high temperature, it becomes ionized; when the ion density is high enough to ensure approximate neutrality, the ionized gas is called a plasma. In addition to electrons and ions, a plasma may be composed of atomic and molecular species in various states of excitation. Excited atoms and molecules are continually produced by collisions with other particles and by absorption of photons, and continually destroyed by collisions with other particles and by emission of photons. Depending on the spatial extent of the plasma and the density of photon-absorbing species, the average photon may be emitted and absorbed many times before reaching the edge of the plasma. In some applications, such as a fusion plasma escaping photons represent an energy sink which cools the plasma, perhaps preventing the proper fusion temperature from being reached. In other applications, such as the plasma of a discharge light source, photons escaping in the wavelength range detectable by the human eye, i.e., between 400 and 700 nm, are not only desirable, but are necessary for proper functioning of the light source. In either case, fundamental understanding of photon emission, migration, and absorption processes in plasmas is indispensable to the researcher. By charter, this Advanced Study Institute is devoted to the study of radiation from discharge plasmas.
KeywordsDischarge Plasma Resonance Line Energy Balance Equation Local Thermodynamic Equilibrium Radiation Efficiency
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