Measurement of Collisional Rate Coefficients for Heliumlike Carbon Ions in a Plasma
Abstract
Measurements of the emitted line intensities from a θ pinch discharge are interpreted in terms of a modified corona model for heliumlike ions. The relative intensities of the resonance and intercombination lines have been measured for C V and O VII as a function of time, as has the absolute intensity of the C v 2^{3}S2^{3}P multiplet. Electron temperatures and densities are obtained as functions of radius and time from the spectrum of Thomsonscattered laser light, and the densities also from Abelinverted absolute continuum intensities. The derived model allows for population of the n=2 levels by direct impact excitation and by cascading, for collisioninduced (exchange) transitions from n=2 triplets to singlets, and for collisional ionization from both the ground and the n=2 triplet levels. Collisional deexcitation of the triplets is shown to be negligible compared with exchange collisions and radiative transitions. Singlet excitation rates (near threshold) are derived with an accuracy of 40% which agree with Seaton and Van Regemorter's semiempirical formulas, triplet excitation rates which are smaller than the singlet rates by a factor 1.8+/0.2, and groundstate ionization rates to an accuracy of 25% agreeing with those estimated from the Bornexchange approximation for hydrogenic ions, suitably modified for twoelectron systems. The measured value for the tripletsinglet exchange rate for C V is equal to 1/5 of the value calculated for He I using the closecoupling approximation, and it has an estimated accuracy of 25%.
 Publication:

Physical Review
 Pub Date:
 January 1968
 DOI:
 10.1103/PhysRev.165.267
 Bibcode:
 1968PhRv..165..267K