Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
SPACE PLASMAS 109 electron gas rises to the point where additional ionization of the neutrals ensues, and a flash ionization of most neutrals occurs. This phenomenon has great significance for models of young solar systems. To perform comprehensive measurements of the processes involved, it will be necessary to achieve the correct physical scale: the electron gas must be heated over a sufficiently large distance that its temperature can rise to the point where impact ionization of the neutrals becomes important to the overall system of interacting gases. Such experiments lie in the future and will require much more extensive supporting resources than have been possible with small free- flying satellites or rockets. Radiation Processes The topic of radiation processes is relatively new and involves detailed study of the production, transport, and absorption of microwave, infrared, and shorter-wavelength radiation in dense plasmas. However, its implication to the study of astrophysical systems is profound. The interaction of such radiation with matter involves individual molecules, atoms/ions, or electronsânot collective plasma processes. Clearly, radiation processes are of fundamental importance in transporting energy through portions of the Sun and of the Earth's atmosphere. In addition, radiation propagating freely from its source and from optically thick regions is the primary means by which remote sensing is accomplished. The opportunity to study fully coupled electromagnetic radiation with plasma dynamics in the space environment supplements the extensive work done in laboratory plasmas on similar problems. ACTIVE EXPERIMENTS Active experiments have a broad range of objectives. The techniques used in active experiments include four main categories: (1) injection of plasma and neutral vapor; (2) injection of energetic beams of neutral particles, ions, or electrons; (3) wave injection from ground based systems of acoustic waves and electromagnetic waves in the very-low-frequency (VLF) and HF bands, or injection from space vehicles of VLF, HF, and microwave radiation; and (4) use of the spacecraft as a disturbance to study spacecraft wake, vehicle charging, ram glow, or the electromagnetic effects of tethered systems. Plasma and Neutral Mass Injections The natural space environment can be modified by the introduction of foreign gases and plasmas to induce or enhance local processes. These include changes of the local ion composition, reduction of the local electron density, changes in the charge state of ions, changes in the average energy of the local
