AAS 204th Meeting, June 2004
Session 51 Improving Our Understanding of Solar and Stellar Coronae
SPD Topical Session, Wednesday, June 2, 2004, 8:30-10:00am, 704/706

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[51.02] Electron-Impact Ionization Measurements Important for Solar Physics

M. E. Bannister (ORNL)

Electron impact ionization (EII) is the dominant ionization mechanism in the solar chromosphere, transition region, and corona. Analyzing spectra from this region of the sun requires accurate ionization balance calculations for plasmas in collisional ionization equilibrium as well as plasmas under conditions of non-equilibrium ionization. Here we report on a series of laboratory measurements of EII that are now underway at the ORNL Multicharged Ion Research Facility for selected ions in the heliumlike, berylliumlike, and oxygenlike isoelectronic sequences. We have found significant errors and uncertainties in the EII data for these isoelectronic sequences, primarily due to uncertainty in the fraction of metastable ions encountered in prior measurements. By determining the metastable ion fractions independent of the ionization experiments, our measurements will provide new EII data for both ground-state and metastable ions with uncertainties of 15% or less.

This material is based upon work supported by NASA under Award No. NNH04AA151 issued through the Sun-Earth Connection Division's Solar & Heliospheric Physics Supporting Research and Technology Program and by the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

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