Ph.D. Thesis, Dartmouth College, November 1995
Space plasmas support a wide variety of oscillatory modes. Some of these wave modes reflect the motion of the particles in the plasma; others can actually accelerate particles or even lead to bulk motion of the plasma. This thesis investigates two types of wave phenomena: electromagnetic ion cyclotron (EMIC) waves in the auroral zone and quasi-thermal fluctuations of electrostatic waves near the plasma frequency.
A sounding rocket detected O+ EMIC waves near 10 Hz in association with ~10 Hz modulations in the downgoing electron flux. From a variety of methods we estimate the source altitude of the EMIC waves to be 5000 km. H+ EMIC waves with a similar source altitude were detected over a wider latitude range on the same flight. A low-energy electron beam in the auroral acceleration region can excite H+, He+, and O+ EMIC waves. Cold plasma ray tracing calculations show that the O+ EMIC waves remain near the field line on which they are generated, while the H+ and He+ waves become spread out over a much wider latitude at lower altitudes.
We have also conducted a theoretical study of quasi-thermal electrostatic fluctuations in unmagnetized plasmas. AMPTE IRM data from the duskside outer plasmasphere shows that emissions near the plasma frequency in this region are often due to quasi-thermal noise and that under favorable conditions the cold electron temperature can be estimated from the amplitude of the plasma line and a direct measurement of the hot electron temperature. We also extend the theory of electrostatic fluctuations to plasmas with a component that has a drift speed below the threshold for instability.
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