Hinode / EIS is operating - is there anything on Fe in the EUV left to be done in the laboratory?

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1 Hinode / EIS is operating - is there anything on Fe in the EUV left to be done in the laboratory? Elmar Träbert Ruhr-Universität Bochum, D-4478 Bochum, Germany, and Lawrence Livermore National Laboratory, Livermore, CA 9455, U.S.A. MSSL, Dec 12, 26 2 Years of Spectroscopy EBI Tsince LA 1986 LIVERMORE in collaboration with P. Beiersdorfer, G. V. Brown, H. Chen, J. H. T. Clementson, D. B. Thorn, a. o. German support by DFG; work at UC LLNL under US DoE Contract No. W-745-Eng-48

2 Fe in the solar corona; EUV 2 35 nm Fe to Fe A matter of temperature and density Properties of laboratory light sources - Laser-produced plasma - Tokamak - Electron beam ion trap (EBIT) - Foil-excited ion beams (beam-foil spectroscopy) - Heavy-ion storage ring Examples of individual techniques or data combinations Time integrated vs. time resolved data Tokamak + LPP + BFS BFS prompt / delayed spectra Lifetime measurements (BFS, storage ring, EBIT) Promising approaches for Fe BFS Spectra of elemental purity BFS Delayed spectra Storage ring E1-forbidden decay rates EBIT High-resolution survey spectra Time characteristics?

3 Atomic level lifetime t = 1/S(Aki) Transition probability Aki Multipole order E1, M1, E2, M2, E3, M3 Resonance lines, high nuclear charge Z: femtosecond lifetimes E1-forbidden lines, not so high charge states: millisecond lifetimes Ultrahigh vacuum: Collision rates of order 1/s Level populations (line ratios) depend on excitation and deexcitation: Density diagnostic Measure radiative decay rates of long-lived levels Optical depth depends on the A-value Extreme cases in astrophysics: All lines in absorption, except for those from extremely long lived levels

4 Properties of laboratory light sources: temperature and density - Laser-produced plasma - Tokamak - Electron beam ion trap (EBIT) - Foil-excited ion beams (beam-foil spectroscopy) - Heavy-ion storage ring Density Solid / Laser-produced plasma cm atoms Gas (1 bar) cm -3 atoms Tokamak 1 13 cm -3 atoms 112 cm -3 electrons EBIT 15 cm -3 atoms 111 cm -3 electrons Solar corona cm -3 electrons Planetary nebulae cm -3 electrons

5 Beam-foil spectroscopy Foil electrons Ion beam Slit Faraday cup Detector Grating x x v = - => t = - t v v Ion velocity x Distance from the foil t Time after excitation

6 1 8 Fe 2 MeV, at the foil Counts 6 4 Beam-foil spectra recorded at the foil (prompt spectra) are very line-rich (excitation under high density conditions) Fe 24 MeV, 175 mm downstream (15 ns) Delayed spectra much more resemble the spectra obtained of the solar corona (low density environment). The lines represent intercombination transitions. Counts Wavelength (nm)

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8 Beam-foil spectroscopy Observation at the foil: The spectrum is dominated by decays of short-lived levels Delayed observation: Much fewer lines, almost no background Signal (log) t << t 1 2 Problem: Long-lived levels ==> little signal per time interval Time

9 Mg Al Si Fe Fe Fe The intercombination lines in Fe XIII and Fe XIV were recognized in beam-foil spectra on the basis of unidentified solar corona observations. The solar data had been recorded with ten times better resolution and accuracy, but it took BFS to tell the element and note the upper level longevity.

10 Beam-foil spectra of Fe top: at the foil (prompt) middle: delayed by about 1 ns bottom: delayed by about 1 ns At the time of measurement, and for years after, even the strongest lines in each of the spectra remained unidentified. By now we know that in the bottom spectrum, most lines are from Fe X and Fe XI. The strongest lines are from levels with lifetimes in the range 1-6 ns. The strongest lines in the solar corona (in this range) have upper levels of lifetimes closer to 6 ns.

11 Counts 5 Fe 7 MeV 25 Ar Beam-foil spectroscopy 5 9 MeV Cl/S/P S The ion beam energy determines the average charge state reached. Lines from particular charge state ions can thus be enhanced or suppressed. 25 x2'=14.6".75"/ch S The delayed spectra shown here were recorded during a search for specific Fe IX (Ar-like, not all of them found yet) and Fe XIII (Si-like, successful search) lines MeV Si S S Si 3 15 MeV P S 15 P P Wavelength / nm

12 Counts 5 7 MeV Delay 5 ns 25 Ar Fe 5 9 MeV Delay 5 ns Cl/S/P S 25 S The ion beam energy defines the charge state distribution after the ion-foil interaction MeV Delay 5 ns P Si S S Systematic variation of the ion beam energy can help to maximize individual spectra and to identify the charge state of origin MeV Delay 5 ns P Si S P P MeV Delay 14 ns P Si P P S Wavelength / nm

13 ns np ns 2 1 S P o E1 1 3 o 1 M2 + hfs hfs P M1 Be - like Mg - like 2 1

14 Heavy-ion storage ring TSR at Heidelberg Circumference 55 m from 12 MV tandem accelerator The ring is mostly used for atomic physics. picture credit: M. Grieser

15 Passive atomic lifetime measurements at TSR Heidelberg Heavy-ion storage ring Channeltrons LiF filter Photomultiplier Injector Beam profile monitor - + Mirror Beam profile monitor - + Beam current monitor Detector of visible / near UV / UV light Detection of VUV / EUV light Atomic lifetime measurements at TSR have reached high accuracy: as little as.14% uncertainty.

16 Transition probability / s Intercombination transition in C III (Be-like) The agreement of experiment and theory, achieved after so many years, is splendid - but not perfect. T T T T T T T T T T E E T E T T T T T T E T T Garstang & Shamey 1967 Nussbaumer 1972 Mühletaler & Nussbaumer 1976 Lin & Johnson 1977 Nussbaumer & Storey 1978 Glass & Hibbert 1978 Laughlin, Constantinides & Victor 1978 Cheng, Kim & Desclaux 1979 Glass 1982 Cowan, Hobbs & York 1982 Kwong et al Smith et al Curtis 1991 Kwong et al Chou, Chi & Huang 1994 Fleming, Hibbert & Stafford 1994 Froese Fischer 1994 Ral'chenko & Vainshtein 1995 Ynnerman & Froese Fischer 1995 Brage, Fleming & Hutton 1996 Doerfert et al Jönsson & Froese Fischer 1997 Froese Fischer & Gaigalas 1997 T Chen, Cheng & Johnson 21 x

17 Fe Kr Mg P Al S Si Cl Be sequence Ne F O N C B Be L J Curtis has derived a mixingangle formalism that interconnects resonance and intercombination line strengths on the basis of spectroscopic data. The heavy-ion storage ring lifetime results on Be-like ions of B through O are internally consistent, but do not agree with the prescribed trend. (Z-2) 2 S r 35 3 Xe 25 Fe Intercombination Kr Ne 2 O 15 N B C /Z Resonance

18 Measurement of M1 and E2 transition probabilities in the ground configuration of ions that are of astrophysical interest o 2 o S P 2 D 124 nm / 135 nm o 3/2 1/2 29 nm nm ms 2.5 ms 11 ms Co XIII nm 12+ (Co ) 3s 2 3p 3 5/2 3/2 3/2 217 nm / 241 nm P - like Fe 11+ Counts ms The line intensities in the ground configurations of N- and P-like ions serve as temperature diagnostics in astrophysics Time (ms) Very few calculations predict all four level lifetimes in P-like ions close to the experimental findings.

19 Isoelectronic trends can be used to ascertain the consistency of data sets. P sequence 3s 23p3 2 D3/2 lifetime P sequence 3s 23p3 2 D 5/2 lifetime 2 8 Garstang 1972 Smith & Wiese 1973 Biemont & Hansen 1985 Biemont 21 Deviation from experiment (percent) Huang 1984 Kaufman & Sugar 1986 NIST 25 Experiment TSR Mendoza & Zeippen 1982 Smitt Nuclear charge Z TSR NIST 25 Kaufman & Sugar 1986 Garstang 1972; Smitt 1976 Mendoza & Zeippen 1982 Smith & Wiese 1973 Nuclear charge Z Huang 1984 Biemont 21 EBIT Experiment Biemont & Hansen 1985 The predicted M1 and E2 transition rates in the literature or on the web (including the NIST data base) are not all as bad as in this case. The problem is how to find out which calculational results are good, and one finds out - by experiment...

20 M1 transition rate in the He sequence 2 Deviation (expt. - theory) (percent) TSR EBIT range Beam-foil spectroscopy range Nuclear charge Z The measurements at the heavy-ion storage ring TSR and at the LLNL EBIT are in excellent agreement with relativistic theory

21 Atomic lifetime measurement in the visible range of the spectrum Livermore electron beam ion trap - the archetypical EBIT Excitation curve in the fast trapping cycle for an atomic lifetime measurement 2 Counts e-beam on e-beam off Cl XIII electron trapping mode ion production magnetic trapping mode fluorescent decay 7 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE Stovepipe for optical observations Time (ms) The basic technique is simple and robust.

22 Counts Cl nm Sum Time (ms)

23 NIST EBIT EST Line Strength (M1) B-like ions n=2 M1 transition between the fine structure levels of the ground state. Predicted line strength S = 4/3. S 1.4 LLNL EBIT LLNL EBIT a p 1.3 HD EBIT TSR TSR LLNL EBIT Line Strength (M1) F-like ions EST Electrostatic ion trap (Kingdon trap) TSR Heavy ion storage ring at Heidelberg EBIT Electron beam ion traps at NIST Gaithersburg, Livermore, and Heidelberg S 1.45 EST EST 1.4 TSR TSR 1.35 LLNL EBIT 1.3 LLNL EBIT Nuclear charge Z

24 The "green iron line" decay curve as seen in the LLNL EBIT Fe XIV Counts Time (ms)

25 The "green iron line" in the solar corona has found plenty of interest Krueger & Czyzak 1966 Warner 1968 Smith & Wiese 1973 Kastner 1976 Kafatos & Lynch 198 Eidelsberg et al Froese Fischer & Liu 1986 Huang 1986 Kaufman & Sugar 1986 Biemont et al Bhatia & Kastner 1993 Moehs & Church 1999 Storey et al. 2 Beiersdorfer et al. 23 Vilkas & Ishikawa 23 Smith et al. 25 Crespo Lopez-U. et al. 26 Fe XIV ab initio ab initio ab initio ab initio Transition rate (s-1)

26 Krueger & Czyzak 1966 Warner 1968 Smith & Wiese 1973 Kastner 1976 Kafatos & Lynch 198 Eidelsberg et al Huang et al Kaufman & Sugar 1986 Biémont et al Bhatia & Doschek 1995 Kohstall et al } Dong et al Moehs & Church 1999 Träbert et al. 24 Fe X ab initio ab initio Texas A&M / Reno TSR (extrapolated) ab initio Transition rate (s-1)

27 E / cm S P 1 3 P D D F F 55 E s 2 3p 3d In Ar-like Kr ions, two lifetimes have been measured of levels with major M2 decay branches. In Ar-like Fe IX, several of the "slow" ground state transitions are still being sought in terrestrial light sources M E1 M1 M2 M1 M1 M1 2 M2 1 E1 3s 2 6 3p Ar - like Fe

28 3 T / 1 cm s 3p 3d s 3p 5 Many ions have a few levels of particularly high J that cannot easily decay (at least not by E1 transitions). These levels act as population traps and are important for charge state distributions s 3p Fe XI J

29 1 S 1 D 3 o F 3 P 3s 2 3p 3d 4 32 In delayed BFS observations, the 3s 2 3p 3d 3 o F 3 level decay has been seen. The decay of the 3s 3p 3d F 4 level has been detected via its influence on an M1 decay curve in the ground configuration. 2 3 o 3s 3p 3 2 3s 3p 2 E2 M2 E2 2 M1 M2 2 1 Si - like Fe 12+

30 Fe ion lifetimes Fe XI 1 D 2 EKT TSR EBIT - I Fe XII Fe XII Fe XII Fe XII 2 o D 5/2 2 o D3/2 2 o P3/2 2 P o 1/2 TSR TSR TSR TSR EKT EKT EKT Fe XIII 1 D 2 EKT TSR Fe XIV 2 P o 3/2 EBIT - I o HD-EBIT o EKT TSR Deviation from best data (percent)

31 Major operating modes of electron beam ion traps Electron beam Ion trapping X-ray production mechanism Magnetic mode Off Magnetic field, drift tube voltage Ion-neutral collisions Electron mode On Electron space charge, magnetic field, drift tube voltage Electron-ion collisions

32 Excitation vs. decay curve Prompt vs. delayed emission 1.5 Ka n=3 7 Time (s) 1..5 Magnetic mode X-rays produced by charge exchange Electron mode X-ray energy (kev)

33 E ion (ev) Ionization energies of Ar q+ ions X X X X 6 X 5 X X 4 X It is easy to reach any charge state of ions in an electron beam ion trap, by adjusting the electron beam energy. In fact, it is too easy to reach any low charge state - there is little selectivity. EBIT does better with higher charge states X X X X X X X X Charge state q

34 In the electron beam ion trap (EBIT), the electron beam energy determines the highest charge state that can be reached. Systematic observations of this kind have been done at Livermore in support of Chandra and XMM/Newton data evaluation. Sample spectra taken from Lepson et al., Ap. J. 578, 648 (22).

35 Multichannel detection is a key element for precision spectroscopy. CCD Detector Focus Wavelength Grating R=44.3 m Grazing incidence flat-field spectrograph at Livermore EBIT 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE This instrument provides the highest spectral resolution of any EUV equipment at any electron beam ion trap.

36 Many EUV spectra can be calibrated with the well known spectral line series of H- and He-like ions a Oxygen O VIII 1-2 O VII 1-2 Signal (arb. units) 5 O VIII O VII 1-3 EUV spectra of oxygen and xenon recorded with a flat-field spectrograph at the LLNL EBIT b Xenon o Wavelength (A) 25 2 c E2 O VII The decays of the lowest excited levels in Ni-like Xe ions have been identified and the wavelengths measured. Signal (arb. unit) Xe XXVII E2 (M1) M3 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE Wavelength (A) o

37 X-ray crystal spectrometers offer high spectral resolution, but suffer from low efficiency XRS Microcalorimeter built at Goddard Space Flight Center for Astro-E / Astro-E2 spacecrafts Covers X-ray energy range 3 ev to 2 kev with 6 ev line width at low E 32 pixels of.6 mm x.6 mm each Working temperature about 6 mk 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE Microcalorimeters feature a poorer resolution than crystal spectrometers, but are much superior to solid state diodes in low-energy access and in resolution.

38 Electron beam on Electron beam off Xe Photon energy (ev) E = 145 ev Time (s) 2 Years of Spectroscopy E BI T LA since 1986 LIVERMORE XRS microcalorimeter data recorded at the LLNL EBIT with a 14 ms trap cycle.

39 Each signal pulse is timestamped; the data can be sorted by X-ray energy or time within the trap cycle. XRS microcalorimeter spectra of Xe (E = 145 ev) Counts (1) d - 4f Xe XXVII 3d - 4p 3d - 4s Xe XXVIII a a) electron beam on b) electron beam off Counts Xe XXVII b Time resolved spectra reflect level population dynamics O VII 4 6 O VIII Years of Spectroscopy E I T LAB since 1986 LIVERMORE Energy (ev)

40 Ni-like Xe XXVII; the transition probabilities shown do not take hyperfine mixing effects into account. D 1 S 1 3D 3d 9 4s 2.6E8 2.49E E2 M1 2 E2 M3 M E8 2.72E8 1.86E4 1.88E d 1

41 When the electron beam is switched off, delayed photons arise from longlived excited levels or from charge exchange (CX) a XRS microcalorimeter data of Xe 1 a) at the position of the M3 decay in Xe XXVII b) at the position of O VIII Lyman alpha Counts (log) b 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE In (near) Ni-like Xe, there is only one level with a long (millisecond range) lifetime Time (ms)

42 Microcalorimeter data of about one week total run time Decay curve extracted from the XRS microcalorimeter data at the position of the Xe XXVII M3 decay Apparent lifetime 11.±.5 ms Counts (log) 1 1 Xe This is the first atomic lifetime measurement using a microcalorimeter at an electron beam ion trap Time (ms) 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE

43 Very few calculations cover the magnetic octupole (M3) decays Safronova 25 Results of LLNL EBIT lifetime measurements on M3 decays in Ni-like ions in comparison to theory (all neglecting any mixing due to hyperfine structure) Lifetime (ms) Other calculations Xe X X Cs Ba A shorter lifetime than predicted makes the ion less sensitive to density effects Nuclear charge Z 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE

44 D 1 S 1 3D 3d 9 4s 2.6E8 2.49E8 2.41E E2 M1 2 E2 M3 M E8 2.72E8 2.65E8 1.86E4 1.88E d 1 Xe XXVII

45 Soft-X-ray signal of Xe at SuperEBIT The even isotope Xe132 has no hyperfine structure. It features a single-component M3 radiative decay (and a tail from charge exchange (CX) processes). Natural Xe has about equal parts of odd and even isotopes and a more complex decay curve. Xe XXVII Counts (log) 1 natural Xe isotopically pure 132 Xe 2 Years of Spectroscopy E I T LAB since 1986 LIVERMORE Time (ms)

46 Now that Hinode / EIS is orbiting, is there anything left to be done in the laboratory? a) The spectroscopy of Fe (and whatever) will be superb from the corona, but the problem of elemental identification has to be taken care of on the ground. There is a historic backlog of spectroscopic misidentifications, because not enough good laboratory data were available 4 years ago. b) Most terrestrial light sources work well with short-lived levels, but those long-lived ones in the corona have to be confirmed. This takes a low density apparatus like EBIT. c) The identification of long-lived levels in the lab takes some time resolution. Time-resolved spectra can harbour surprises. Consider the example of the metastable level in Ni-like Xe, that only recently has been explicitly left out of an extensive calculation. Microcalorimeter data on Xe demonstrate how the spectrum dynamics depend on a long lived level. In the soft part of the EUV, a different device will be needed, for example a microchannel plate-based detector (MCP).

47 Laboratory work on the EUV spectrum of Fe: Needs elemental purity, add time resolution Working ranges Beam-foil spectroscopy : picosecond to hundred nanoseconds Electron beam ion trap : femtosecond and microsecond to hundred milliseconds Heavy-ion storage ring : millisecond to dozens of seconds Atomic lifetimes (E1-forbidden decays) are of interest in - astrophysics (solar corona, planetary nebulae, AGN, etc.) - plasma physics (tokamak, spheromak, divertor) EBIT experiments offer high spectroscopic accuracy Beam-foil data guarantee isotopic purity, reasonable charge state discrimination 2-35 Å range: Beam-foil data on Fe are available, EBIT data may become available in a few years Heavy-ion storage ring lifetime experiments are in progress