Creating and Characterizing an X-ray Photoionized

Nebula in the Laboratory

David H. Cohen1,2, Joseph J. MacFarlane1, Duane Liedahl3, James E. Bailey4

1Prism Computational Sciences, Madison, Wisconsin

2Bartol Research Institute, University of Delaware

3Livermore National Laboratory4Sandia National Laboratory

Presented at the NIF Science Workshop, Pleasanton CA, 5 October 1999

We are entering a new era of astrophysical X-ray spectroscopy

Mission LaunchDate

SpectralRange

SpectralResolution

EffectiveArea

(keV) () (cm2)

Einstein 1978 0.4 – 4.0 3 100ROSAT 1990 0.1 – 2.4 2 200ASCA 1993 0.5 – 12 20 1000

Chandra gratings 1999 0.1 – 10 600 1000XMM 2000 0.4 – 2 300 100

ASTRO-E 2000 0.5 – 12 1000 200

(Chandra)

The first Chandra spectra are available

At a resolution approaching = 1000 (300 km s-1), line complexes such as the helium-like triplets can be separated…

However, line profile analysis is not possible in most (but not all) cases

Historically, the most-studied cosmic X-ray sources have been coronal--

primarily the Sun

However, many interesting X-ray sources are not coronal/collisional, but rather are photoionized

These tend to involve compact objects, which are a source of hard, continuum X-rays -- AGG/Quasars, X-ray Binaries,…

...but any environment where relatively cool plasma coexists with a strong source of X-rays will require photoionization

modeling to understand

X-ray emission characteristics of photoionized plasmas:

•radiative recombination continua

•recombination cascade emission lines

•fluorescent emission

•inner-shell absorption

Spectra of X-ray photoionized plasmas are quite different from collisional plasmas

Photoionized plasmas

•Characterized by the ionization parameter, =L/nR2

typically 1 < log < 4 in photoionized astrophysical sources

•value of controls ionization level

•if ne is low enough, then level populations are set by photoion./photoexcit./2-body recombination/spont. emission

(upper levels are populated by recombination cascades, not collisions)

photoionizedcollisional

High quality data from XRBs, AGNs are coming

Current state of the art is ASCA(until Chandra)

In this low-resolution spectrum of the XRB Cyg X-3 the only overt sign of photoionization’s dominance are the radiative recombination continua

- note that they are narrow because of the low plasma temperature, which is so low that the high ionization states we see cannot be produced by collisions

Soon to have high resolution X-ray spectra of cosmic sources

Detailed absorption spectroscopy of photoionized sources such as this micro-quasar

(ASTRO-E simulation)

Also will resolve individual emission lines from radiative recombination cascades and fluorescence in sources like Cyg X-

3

Collisional plasmas have been studied extensively (e.g. in tokamaks and solar spectra) and detailed spectral models

exist (MEKAL, Raymond-Smith) but much less work has been done with photoionized plasmas, both

observational/experimental benchmarking and modeling

collisional vs. radiative plasmas high vs. low density

In the laboratory, radiation interaction with high-density (optically thick) plasmas leads to shock waves and gradients

But, X-rays are absorbed volumetrically in low density gases potential for relatively gradient-free plasmas

Radiation from left onto solid KCl

How can the NIF contribute to our understanding of photoionization-dominated astrophysical plasmas?

Schematic of argon gas experiment

•Spectra will be a guide to identifying features in astrophysical data

•Spectra will be used to benchmark, and drive the improvement of, codes

Emission spectroscopy

Absorption pectroscopy (also, direct measurement of the converter)

Converter (laser to X-rays)

Laser beams

Gas target

X-raysFluence of 1010 ergs with high-Z foil on NOVA

1012 ergs on NIF, and if n=1018 cm-3 and R=1 cm then =103

Hydrodynamical simulation of gas photoionization experiment

~10-5 g cm-3 (1% normal density)

(TR=250 eV subtending 1 ster)

Normal density~10-5 g cm-3)

minor opacity effects, gradients (and numerical noise)

Predicted Spectra(5 ns, normal density)

absorption spectroscopy (K-shell) = ionization balance

emission spectroscopy (L-shell) = temperature

Issues to address

•X-ray converter -- foil or under-dense radiator?

•Target -- gas jet or gas bag? (how low in density can we go?)

•Diagnostics -- spectroscopy of :

•ionizing source

•recombination emission from gas

•backlit absorption from gas (for ionization balance) - using converter? Separate backlighter?

•Other - DANTE-type absolutely calibrated measurement

•Equilibration times

Why NIF?

•More X-rays to go for higher ionization parameter,

•Harder X-rays to ionize directly out of the K-shell and to look at higher-Z plasmas

•Longer duration (using multiple, staggered beams) to get closer to ionization equilibrium