2008 Articles

Analog and Digital Simulations of Maxwellian Plasmas for Astrophysics

Savin, Daniel Wolf; Badnell, N R; Beiersdorfer, P; Beck, B R; Brown, G V; Bryans, P; Gorczyca, T W; Gu, M F; Kahn, S M; Laming, J M; Liedahl, D A; Mitthumsiri, W; Scofield, J H; Wong, K L

Many astrophysical and laboratory plasmas possess Maxwell–Boltzmann (MB) electron energy distributions (EEDs). Interpreting or predicting the properties of these plasmas requires accurate knowledge of atomic processes such as radiative lifetimes, electron impact excitation and de-excitation, electron impact ionization, radiative recombination, dielectronic recombination, and charge transfer, all for thousands of levels or more. Plasma models cannot include all of the needed levels and atomic data. Hence, approximations need to be made to make the models tractable. Here we report on an “analog” technique we have developed for simulating a Maxwellian EED using an electron beam ion trap and review some recent results using this method. A subset of the atomic data needed for modeling Maxwellian plasmas relates to calculating the ionization balance. Accurate fractional abundance calculations for the different ionization stages of the various elements in the plasma are needed to reliably interpret or predict the properties of the gas. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. Here we will also review our recent updating of the recommended atomic data for “digital’ computer simulations of MB plasmas in collisional ionization equilibrium (CIE), describe the changes relative to previously recommended CIE calculations, and discuss what further recombination and ionization data are needed to improve this latest set of recommended CIE calculations. PACS Nos.: 34.70.+e,34.80.Dp, 34.80.Kw, 34,80,Lx, 52.50.–j, 52.20.Fs, 52.20.Hv, 52.25.Jm, 52,72.+v, 52.75.–d, 95.30.Dr, 95.30.Ky, 98.38.Bn, 98.58.Bz