Hot-electron production, anomalous absorption, and effect of intense electromagnetic fields on inverse bremsstrahlung absorption near the electron plasma frequency
Measurements are presented of anomalously large microwave absorption near the electron plasma frequency $omega$/sub p/ by a completely ionized plasma. The threshold electric field required for the onset of anomalous absorption has been measured over a density range that is large enough to separate clearly the effects of Landau and collisional damping. Good agreement is demonstrated between these measurements and the threshold values predicted by a computer solution of the exact dispersion relation for AC parametric instabilities. Energy distribution measurements are presented for the hot, non-thermal electron tail produced by such anomalous absorption. The nature of these distributions depends strongly upon ($omega$/sub p//$omega$$)$$sup 2$ and microwave power. In some cases a large fraction of the anomalously absorbed power goes into less than 1 percent of the electrons and a bump develops on the hot tail. Below the threshold for anomalous absorption, the classical electron-ion collision rate, v/ sub ei/, from a measurement of the inverse bremsstrahlung absorption rate has been deduced. The first experimental evidence that intense electromagnetic fields modify v/sub ei/ is reported. Observations from these experiments yield a simple empirical relation that applies for AC drift speeds as large as eE/ (m$omega$) approximately (kT/sub e//m)/sup 1/2/. Ohmic heating is minimized in these experiments by use of very short microwave pulses. (auth)
- Research Organization:
- Los Alamos Scientific Lab., NM
- NSA Number:
- NSA-33-005388
- OSTI ID:
- 4173037
- Resource Relation:
- Conference: 5. conference on plasma physics and controlled nuclear fusion research, Tokyo, Japan, 11 Nov 1974; Other Information: See STI/PUB--381(Vol.2); CONF-741105--P2. Orig. Receipt Date: 30-JUN-76; Related Information: Plasma physics and controlled nuclear fusion research, 1974. Vol. II
- Country of Publication:
- IAEA
- Language:
- English
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