Heavy Elements Transition Probability Data of Interest in Astrophysics and Divertor Physics

1. Heavy Elements Transition Probability Data of Interest in Astrophysics and Divertor Physics Betsy Den Hartog University of Wisconsin - Madison Madison, WI USA IAEA RCM Heavy Element Data Needs Vienna 14 - 15 Nov 2005

2. Collaborators • Jim Lawler – University of Wisconsin • Chris Sneden – University of Texas • John Cowan –University of Oklahoma

3. Outline • Review - transition probability effort at the University of Wisconsin • Current work - progress in astrophysics • Future work in aid of divertor diagnostics and modeling

4. Transition Probability Effort at the University of Wisconsin–Madison

5. Large sets of transition probabilities have been measured at UW for 1st and 2nd spectra of many heavy elements. • gA values are determined from a combination of techniques to measure radiative lifetimes and branching fractions. • Current focus is on elements of astrophysical interest: Sm II and Gd II

6. Transition probabilities are determined by combining branching fractions and radiative lifetimes. u A3 A2 A1 • Branching Fractions are determined from relative intensity measurements using Fourier-Transform Spectroscopy. • Radiative Lifetimes provide the absolute normalization for determining transition probabilities.

7.  and gA measurements at Wisconsin - 47 spectra measured- most elements could be measured

8. Techniques used are broadly applicable and efficient. • Combined techniques used to measure BF’s and ’s allows for large sets of data measured to good accuracy (’s 5%, gA’s 5-20%). • In past ~9 years - > 1400 ’s published for 16 spectra, >3600 gA’s published for 13 spectra.

9. Radiative lifetimes are measured using time-resolved laser-induced fluorescence on a slow atom/ion beam. • Advantages of LIF Technique • 5% uncertainty for most levels • selective excitation - no cascade repopulation • broad applicability - most elements of periodic table accessible • broad accessibility - levels from ~15,000 - ~60,000 cm-1 can be studied (using UV/VIS laser) • wide dynamic range- 2 ns to >2 s • no collisional quenching or radiation trapping

10. The experimental apparatus is simple and robust. anode Trigger generator Pulsed power supply side view Nitrogen laser dc power supply Tunable dye laser cathode Frequency doubling (when needed) Atomic beam Diffusion pump

11. Schematic of Experiment - top view Atomic beam Tunable laser radiation Fluorescence Fused silica window and lenses Spectral filters Transient digitizer PMT

12. Sample Fluorescence Data • Data collection: • begins after laser terminates • each decay is divided into 2 analysis regions • each region ~1.5 in length Recorded fluorescence 1st analysis interval 2nd analysis interval

13. Branching fractions are determined from spectra recorded using a 1 m Fourier-transform spectrometer. • Advantages of Technique: • excellent resolution - resolution is Doppler limited, reducing blending in rich spectra • excellent accuracy - 1:108 wavenumber accuracy • fast collection rate - 1 million point spectrum in 30 minutes • broad spectral coverage - UV to Infrared • simultaneous collection - data collected in all spectral elements of interferogram simultaneously - crucial for relative intensity measurements

14. Sample FTS spectrum

15. In near future, VUV spectrometry capability will be in place at UW. • VUV lifetime experiment already in place. • Spatial Heterodyne Spectrometer is currently under development (NASA funding). • SHS will be used for VUV Branching Fractions (300 nm - 150 nm this year; 300 nm - 100 nm next year). • SHS suitable for multiply ionized species.

16. Advantages - SHS • preserves advantages of Michelson FTS -high spectral resolution, étendue, high data collection rates, and simultaneous collection on all spectral elements • reflecting beam splitter -eliminates the VUV optics issues of the transmitting beam splitter by use of a grating operated in Echelle mode as beam splitter • no moving parts -can be used in “flash” mode making it suitable for multiply-ionized species

17. Update on Current Work - progress in Astrophysics • In past 6 months - • completed a very large work on Sm II gA’s • (> 200 ’s, > 900 gA’s) and astrophysical Sm abundances • ~3/4 through measurements of Gd II gA’s • extension to the VUV progressing with the Spatial Heterodyne Spectrometer

18. Progress ReportAll-Reflection Spatial Heterodyne Spectrometer -- optics mounts built- optical table purchased- initial tests this week using small detector array

19. Sm II gA measurements • fairly extensive work on ’s in literature • only 2 reported independent determinations of BF’s • Saffman and Whaling - measured BF’s using a grating spectrograph • Xu, et al - determined BF using HFR calculations

20. Sm II gf values - Comparison with other experimental measurements SW BF’s measured using a grating spectrometer are combined with our measured lifetimes for comparison. Saffman L., & Whaling W. 1979, J. Quant. Spectrosc. Radiat. Transfer, 21, 93

21. Sm II gf values - compared with HFR calculations Xu, et al - BF determined with HFR combined with measured lifetimes HFR Calculations: Xu, H. L., Svanberg, S., Quinet, P., Garnir, H. P., & Biémont, E. 2003b, J. Phys. B: At. Molec. Opt. Phys., 36, 4773

22. Same comparison vs log(gf) value

23. Same comparison vs Eupper

24. Comparisons of measured lifetimes Radiative lifetimes are not a significant source of the discrepancy between measured and calculated gf values

25. Astrophysical Application to Sm II abundance Solar photosphere - scatter is much reduced from earlier determinations log ε(A) = log10(NA/NH) + 12.0

26. Application to a metal-poor halo star BD +17 3248 Many more lines employed and scatter reduced x3 log ε(A) = log10(NA/NH) + 12.0

27. Metal-poor galactic halo stars are being studied to understand early galactic evolution and the details of nucleosynthesis. Abundance determinations are improving element by element.

28. Future work - UW contribution to CRP • gA’s for W II, Mo II, UV/VIS gA’s for levels up to ~50,000 cm-1 • VUV gA’s for higher levels • improved wavelengths as needed

29. Summary • Large sets of gA’s (UV/VIS) are routinely measured to ± 5 - 20% for neutral and singly-ionized species. • Sm II gA’s and astrophysical application recently finished, Gd II underway • Near-future capabilities include VUV branching fractions and lifetimes • We hope to expand the gA and  database for species of interest for diagnostics and modeling of the edge plasma (W II, Mo II, others?).