Collisional Coefficients Research Articles

Relation between bounce-averaged collisional transport coefficients for geomagnetically trapped electrons

The unweighted bounce average (N/sub j/) of the atmospheric density N/sub j/ along a field line and the weighted bounce average are related (for each atmospheric constituent j) by an integral or derivative with respect to y, the sine of the equatorial pitch angle ..cap alpha../sub 0/, where B/B/sub 0/(=y/sup -2/ sin/sup 2/ ..cap alpha..) is the ratio of local to equatorial magnetic field intensity and ..cap alpha.. is the local pitch angle. The unweighted bounce average is relevant to energy deposition by radiation belt particles of all species, while the weighted bounce average is relevant to the description of pitch angle diffusion of radiation belt electrons. (AIP)

Fluorescence efficiencies of nitrogen and air excited by neon and sodium ions at 0.3–2.0 MeV

The fluorescence efficiencies for excitation of nitrogen and air by neon and sodium ions have been measured at bombarding energies between 0.3 and 2.0 MeV. The molecular spectra studied were the first negative system of N2+ (1N) and the second positive system of N2 (2P). The atomic spectra studied were the N+ 5003 Å multiplet and the N+ 5680 Å multiplet. The fluorescence efficiencies of the 3914 Å band and the 4278 Å band of the 1N system and the 3371 Å band of the 2P system were derived directly from the fluorescence data as were the efficiencies of the 5003 Å and 5680 Å multiplets. Efficiencies relative to the 3914 Å band were estimated for the (ν′ = 0, ν″ = 0–3) bands of the 1N system and the (ν′ = 0, ν″ = 0–5), (ν′ = 1, ν″ = 0–6), and (ν′ = 2, ν″ = 2–7) bands of the 2P system. In addition, collisional deactivation coefficients for the 5003 A and 5680 A multiplets were derived from the efficiency data. The efficiencies of all spectra studied increased with increasing energy, with the efficiency of the 3914 Å band being the largest (0.48%) at 2.0 MeV for Ne+ in N2. The ratio of the intensity of the 4278 Å band to that of the 3914 Å band indicates that the Franck-Condon principle is obeyed in this particular case. Also, the ranges of neon and sodium in nitrogen and air were obtained from emission measurements.

Excited atoms in decaying optically thick plasmas

With attention confined to decaying H-H+-e and He-He+-e plasmas which are optically thick towards lines ending on the ground level, the quasi-equilibrium number density of atoms in the first excited level nQ'(2) is computed using collisional deactivation coefficients K(2, 1) based on experiment and taking Penning ionization into account. This last is discussed in some detail. Quantal calculations are carried out on the rate at which the electronic transitions involved in 2H(2s-p) -> H(1s) + H+ + e occur. It is concluded that the rate is probably fast enough for almost all close collisions to lead to ionization. This also seems to be the case for 2He(2 3S) -> He(1 1S) + He+ + e provided collisions which can yield ionization only by violation of Wigner's spin conservation rule are excluded from consideration. Penning ionization is of little importance in hydrogen plasmas, but it can be significant in helium plasmas where it tends to reduce nQ'(2) and the apparent recombination coefficient.

Role of Hard-Core Collisions with Large Angle Deflections in the Kinetic Theory of Dense Fluids

The validity of the Fokker—Planck equation is discussed within the framework of Kirkwood's time smoothing formalism. It is shown that the equation is equivalent to the Boltzmann equation for a dilute homogeneous system in which grazing binary collisions predominate. Using this as a mathematical prescription, the Rice—Allnatt equation is modified by replacing the Boltzmann collision integral by a Fokker—Planck operator, but leaving the excluded volume term unchanged. The kinetic and collisional transport coefficients derived from the modified equation are compared with those derived from the Chapman—Enskog equation, the Rice—Allnatt equation, and the Fokker—Planck equation. It is concluded that the role of hard core collisions in the theory is to emphasize the importance of large angle deflections, which are not important in a dilute gas.