Kinetic Theory of the Inner Magnetospheric Plasma by George V. Khazanov

Author:George V. Khazanov
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

7.3.5.1 The Photoelectron Source Spectrum

An important feature of the PE source spectrum is the presence of spikes due to specific emission lines in the solar EUV spectrum. A prominent line is the He II 30.4-nm line. With an energy of 40 eV, this strong line produces a series of peaks in the 20–30 eV electron energy range due to the various ionization states of the atmospheric constituents.

Another important feature of the photoelectron source spectrum is the presence of the Auger electron peaks. This is due to the double ionization of atmospheric particles by high-energy photons. These photons initially produce a free electron from an inner electron shell of the neutral. Then an electron from the outermost shell transitions down to fill the hole, releasing a photon equal to this transition energy. This photon, however, does not escape but instead produces another free electron from the outermost shell. This second electron is known as an Auger electron, and has an energy of 300–500 eV, depending on the particle it originated from. There have been only a few modeling efforts to include this population (Avakyan et al. 1977; Winningham et al. 1989), showing that the inclusion of Auger electrons is necessary to obtain good agreement with observations while maintaining reasonable soft X-ray solar fluxes. For the present section, which focuses on the comparison of PE fluxes with PSE fluxes in the inner magnetosphere, Auger electrons are a critical component of the results.

As discussed above, the field-aligned model provides a source term for the bounce-averaged model at the LCB on the dayside for the PEs. For the cases to be examined here, a moderately high solar activity level will be used along with various geomagnetic activity levels. The PE source is mostly a function of solar activity level, and largely independent of geomagnetic activity. Therefore, the PE source term being supplied to the bounce-averaged model is essentially the same for the various simulations. A typical LCB spectrum is shown in Fig. 7.15. The low-energy range below 5 eV is sloped upward due to Coulomb collisional damping, the production peaks are essentially washed out into a single increase in flux near 25 eV, and the Auger peaks at 300 and 500 eV are quite distinguishable. Note that there is actually fine structure present in the Auger production peaks (see Chap. 2 resulting from the individual ionization states of the atmospheric constituents, and the resolution of this fine structure (and that in the 20–30 eV range, Fig. 7.11) is highly dependent on the energy step of the model. The choice of a geometrically increasing energy step for these calculations smooths out the peaks, especially in the high-energy range. Choosing a ΔE of much less than 1 eV is necessary to accurately resolve each peak (cf. Jasperse and Smith 1978), and the stability of these peaks have been debated as a source of plasma waves (Khazanov 1979). In this chapter, because we are interested in the global formation and evolution of the distribution function rather than the possible instabilities (see Chap.

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