Slide 1

X-Ray Measurements Using a Microcalorimeter on an Electron Beam Ion Trap E. Silver, N.S. Brickhouse and H. Schnopper Harvard-Smithsonian Center for Astrophysics G.X. Chen and K. Kirby Institute for Theoretical Atomic and Molecular Physics J.D. Gillaspy, J. N. Tan, J. M. Pomeroy National Institute of Standards and Technology J. M. Laming Center for Space Science, US Naval Research Laboratory High Accuracy Atomic Physics in Astronomy August 79, 2006 Slide 2 Microcalorimeters Are No Longer a Laboratory Curiosity! X-ray astronomy(SAO,GSFC,U of WI, NIST (B), OAPA) Laboratory astrophysics (SAO,NIST(G), LLNL, GSFC, OAPA) Materials science (SAO, NIST(B), LLNL) Particle astrophysics (U of Cal, LBNL) Surface physics (SAO, NIST (G)) Heavy ion spectroscopy (SAO, GSI, U of WI, GSFC) Mass spectroscopy (LLNL) Biological analysis (SAO) Briefly explain why these detectors represent such a discontinuous jump in performance & Highlight a range of EBIT measurements & Present our latest theoretical and experimental work on neon-like Fe and Ni & Discuss how to tackle important issues to improve measurement accuracy Slide 3 Microcalorimeter Absorber Thermometer X-ray Weak thermal link (Aluminum Wires) Heat Sink Temperature Slide 4 Microcalorimeter Tin Absorber NTD Thermistor Heat Sink Aluminum Wires Require small C Low T Low noise readout Goal Measure < femtojoule (10 -15 joules) With precision of 1 part in 1000 (atojoule) Over dynamic range > 100 Slide 5 Sn Absorber NTD Thermistor Weak thermal link (Aluminum Wires) Heat Sink Temperature X-ray Resistivity vs T -1/2 for samples of NTD Ge available for thermistor use SEM micrograph of single pixel NTD-Ge microcalorimeter with Sn absorber JFET Feedback Resistor Thermistor Bypass Capacitor Current Source V constant, R Signal: V = I R F Voltage Slide 6 Soft X-Ray Performance 0.35 mm x 0.35 mm x 7 m tin absorber + NTD 17 Ge thermistor Slide 7 Slide 8 The EBIT was invented in 1988 ago by Mort Levine at LBNL The first EBITs were built in the US, first at LLNL, then at NIST Today there are machines in the UK, Germany, and Japan soon there will be one at CfA ! Spectral lines are emitted by multiply charged ions, which are created and trapped under well controlled conditions Every charge-state of every astrophysically important element can be created Conditions are very similar to the plasmas of the solar corona The Conventional Electron Beam Ion Trap (EBIT) Slide 9 Capabilities Selection of specific charge states Simulating specific slices of astrophysical conditions Measurements of atomic data of elementary processes electron impact ionization-, and excitation cross sections radiative- and dielectronic recombination processes excited state lifetimes charge exchange cross sections precision x-ray wavelengths X-ray polarization measurements Ions at rest electrons with nearly constant energy fast switching of voltages Slide 10 Ion Beam Extraction For Surface Physics NIST Group R. Schuch University of Stockholm D. Schneider LLNL Extracted Ions EBITMicrocalorimeter Ion Surface Interactions Electron Capture into High n-states forms Hollow Atoms Slide 11 Spectroscopy of Trapped Ions in an Electron Beam Ion Trap Silver et al., ApJ 541 (2000) 495. Laming et al., (2000), Ap.J., 545, L161. He-like and H-like N and O Ne-like Fe XVII He-like Ne Slide 12 Liquid He 4 K 90 K 180 K ADR and Detectors Heat Exchangers Windows Cryostat with 2-Stage ADR 1 x 4 pixel NTD Ge array Detectors kept at temperature of 60 mK +/- 1 K rms for 52 hours) Windows: 4 x (800 polyimide, 500 aluminum) Built-in x-ray tube for calibration SAO-NIST NTD Microcalorimeter EBIT SET-UP EBIT X-ray beamline Microcalorimeter inside EM shield Slide 13 Broad band measurements of He-like Argon Sample of measurements using new microcalorimeter at NIST Ne-like Fe XVII Slide 14 FeXVII produces some of the strongest lines observed in astrophysical and solar X-ray observations. Its diagnostic capability, however, has been limited because the line formation mechanism is not well known and early spectral modeling codes had large uncertainties. In many instances the ratio of R1=3C/3D was frequently much lower than predicted by theory. The ratio of complete 3s to complete 3d transitions is also frequently larger than predicted by theory. This has been an ongoing challenge to theory. Status of neon-like FeXVII and Ni XIX as a Diagnostic For Astrophysical Plasmas EBIT Measurements C D E G M2 F Active Binary HR1099 as observed by CHANDRA HETG Slide 15 Some Recent Papers on Fe XVII 1.Brown, 1998 (crystal) Ap. J. 502, 1015 (1998); see also 532, 1245 (2000). 2.Laming, et al 2000 (microcalorimeter) Ap. J. 545, L161 (2000). 3.Brown 2001 (crystal) Phys. Rev. A 63, 032719 (2001). 4.Beiersdorfer 2002 (crystal & microcalorimeter) Astrophys. J. 576, L169 (2002). 5.Chen and Pradhan 2002 (theory) Phys. Rev. Lett. 89, 013202-1 (2002). 6.Gillaspy 2004 (microcalorimeter) CP730 (AIP, New York) 245 (2004). 7.Chen and Pradhan (preprint; theory) 8.Fournier and Hanson 2005 (theory) Phys. Rev. A 71, 012717 (2005). 9.Loch, et al 2006 (theory) J. Phys. B 39, 85 (2006). An ongoing saga! Slide 16 THE PROBLEM Agreement between NIST and LLNL measurements is not satisfactory Neither NIST nor LLNL measurements agreed with early theory. Slide 17 Figure from Beiersdorfer, 2003 (review) Chen & Pradhan, 2002 First, a look at the discrepancy with theory... The interpretation of experimental and observational ratios of line intensities has usually relied on collisional-radiative (CR) models such as those using theoretical cross-sections that neglect the fundamental role of resonant excitation. Resonant excitation preferentially affects the forbidden and intercombination transitions as opposed to dipole allowed ones. While the 3C (=15.014 ) line is dipole allowed, the 3D (=15.265 ) and 3E (=15.456 ) are spin- forbidden intercombination transitions. The majority of calculations to date has used the distorted wave (DW) approximation that neglects channel coupling and hence, resonances. Slide 18 Pradhan and Chens calculations are perhaps the largest scale e-ion scattering calculations to date (for any system). Dimension of Hamiltonian=10286 89 level eigenfunction expansion 395 free channels 486 bound channels 20,000 energy points on grid Slide 19 Resonances are a key part of the Chen & Pradhan (2002) calculation--they result in oscillations as a function of energy.