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

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

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

Transition Probability Effort at the University of Wisconsin–Madison

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

u A3A3 A2A2 A1A1 Transition probabilities are determined by combining branching fractions and radiative lifetimes. Branching Fractions are determined from relative intensity measurements using Fourier-Transform Spectroscopy. Radiative Lifetimes provide the absolute normalization for determining transition probabilities.

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

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. Techniques used are broadly applicable and efficient.

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 Radiative lifetimes are measured using time- resolved laser-induced fluorescence on a slow atom/ion beam.

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

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

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

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 - 1:10 8 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

Sample FTS spectrum

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 nm this year; 300 nm nm next year). SHS suitable for multiply ionized species.

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

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

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

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

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

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

Same comparison vs log(gf) value

Same comparison vs E upper

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

Solar photosphere - scatter is much reduced from earlier determinations log ε(A) = log 10 (N A /N H ) Astrophysical Application to Sm II abundance

Application to a metal-poor halo star BD log ε(A) = log 10 (N A /N H ) Many more lines employed and scatter reduced x3

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

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

Summary Large sets of gA’s (UV/VIS) are routinely measured to ± % 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?).