Photoionization of trapped ions at synchrotrons and

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2 Photoionization of trapped ions at synchrotrons and free-electron electron X-ray X lasers José R. Crespo López-Urrutia Sascha W. Epp,, Martin C. Simon, Maria Schwarz, Christian Beilmann Max-Planck Planck-Institut für f r Kernphysik Heidelberg

3 Our closest highly ionized neighbor

4 Saariselkä at the other end...

5 Why highly charged ions (HCI)? Naturally abundant: warm hot intergalactic medium (WHIM, this backdrop) may comprise half of the missing baryonic matter! QED fully loaded electrons to benchmark relativistic ab initio theory Electron-electron correlations can be tuned from simple (H-like) to complex (He-like, etc.) Important for fusion research plasmas

6 Follow the bound-state QED experts...

7 QED scales with Z 4 only a few ev accuracy needed since effects are very large

8 Asymmetry due to quantum interference

9 1e QED 4 ev 2e QED 0.2 ev recoil 0.08 ev 0.04 ev uncertainty Mid-heavy ions studied with electrons, X rays

10 The He-like1s2p 1 P 1-1s 21 S 0 resonance line w Z Artemyev Drake Experiment Ref. This work Remarks (9) [1] (3) Absolute, 3x (38) [2] (4) Absolute, 10x (1) (200) [3] (13) Absolute, 7x (250) [4] In Fe 24+ contribution to this transition of: 4 ev QED, 200 mev screened QED, 100 mev nuclear recoil contributions vs. 13 mev uncertainty [1] L. Schleinkofer et al., Phys. Scr. 25, 917 (1982) [2] R. D. Deslattes, H. F. Beyer, and F. Folkmann, J. Phys. B 17, L689 (1984) [3] P. Beiersdorfer et al., Phys. Rev. A 40, 150 (1989) [4] J. P. Briand et al., Phys. Rev. A 29, 3143 (1984)

11 Two-electron QED Contributions to ground state in He-like Ar ev 5 ev 1 ev + + h. o. experimental error bar: 0.01 ev E nuclear recoil 0.06 ev higher orders ev 0.1 ev

12 Forbidden lines with laser spectroscopy

13 Relativistic nuclear recoil seen: 40 Ar/ 36 Ar isotopic shifts in forbidden transitions Ion Ion NMS SMS RNMS RSMS FS Total Ar Ar Normal mass shift (NMS), specific mass shift (SMS) and their relativistic corrections (RNMS, RSMS) are similar in size Theory λ (nm,air)* λ Observed (nm) Isotopic shifts ( 40 Ar/ 36 Ar) theory(nm) experiment(n m) Ar (27) (1) (2) Ar (30) (3) (7) Results agree with recent predictions (Shabaev)

14 CryPTEx: Cryogenic Paul trap for HCI spectroscopy Laser spectroscopy on sympathetically cooled HCI

15 Redistribution of energy by radiation Light is faster than shocks, even than relativistic jets X rays shift more energy around than visible light In astrophysics, parameter is the ratio of photon flux (ergs/cm 2 s) over electron density N =4 I/N ratio of photoionization over collisional ionization In astrophysics typically10< <10000 In laboratory up to <10 (lasers, Z pinches) With LCLS and EBIT, < possible (at low N)

16 Around black holes, neutron stars, X rays generated by infalling matter photoionize the surroundings: Photoabsorption is seen Black holes glow; Fe K-shell radiation is the last cry of matter

17 The identification problem Existing atomic models have large wavelength uncertainties and lack experimental confirmation Only 100 lines identified out of 950!

18 The Fe L-shell autoionizing resonances carry 60% of total PI strength, dominating over the direct channel PI cross section (cm 2 ) Integrated PI strength (cm 2 ev) x x x10-16 Direct PI cross section Total PI cross section Total strength Resonant strength Direct photoionization strength Planck continuum Cross section weighted with Planck continuum Photon energy (ev) Resonances dominate!

19 X-ray absorption spectra of quasars X-ray spectra of quasars show HCI in their outflows. Fe ions are prominent Uncertainties of different models for calculating spectra are too large for Doppler shift speed determinations

20 The warm-hot intergalactic medium (59 ± 9) % of baryons are missing 30 Mpsc To hot for visible light, too diffuse for direct X-ray detection Cosmological simulations (Cen & Ostriker) predict a warm-hot interstellar medium (WHIM) heated by gravitation to 10 6 K containing most of the missing baryons Discovery by Nicastro (2005)?

21 How to detect WHIM For very tenuous media, measurements in absorption are far more sensitive than those in emission Chandra Backlighting quasar medium absorbing radiation Spectrum shows absorption lines Details matter! You may miss half the mass of the universe!

22 WHIM and interstellar medium absorption Detective work: figure out red shift <z>, identify lines, determine temperature, infer density of metals, He + and H + Local Group WHIM <z>=0.011 WHIM <z>=0.027 WHIM

23 Details matter! You may miss half of the mass of the universe! Newer observations confirm WHIM (Fang et al.)

24 The opacity problem Radiation transport inside the Sun is determined by opacity of Fe, Ne, O at temperatures 200 to 500 ev Fe are essential Helioseismographic data disagree with models: opacities are only calculated!

25 Photonic interactions with HCI Combine novel high energy photon sources (free electron lasers, synchrotrons) with EBIT to measure excitation energies beyond current accuracy limits to study multiphoton processes to determine cross sections for photoexcitation, photoionization HCI benchmarking atomic theory

26 HCI production with electron beam ion trap I beam =450 ma radial potential electron beam space charge axial potential electrodes A/cm 2 n e e - /cm 3 Electron beam drives ionization and traps

27 Sascha s EBIT

28 z coordinate FEL principle Radiation field interacts with electron bunch and structures it Electron beam Radiation

29 Coherent superposition enhances intensity by a factor proportional to the number of charges in the bunch N e Dipole Wiggler Undulator Undulator Brilliance increases by many orders of magnitude

30 The free electron laser FLASH Accelerator hall Free electron LASer in Hamburg Undulator tunnel 240 m E max = 200 ev E/ΔE nat. 100 t pulse 2*10-14 s E pulse 50 μj 500 pulses/s 240 m Experimental hall

31 Photoexcitation of HCI in an EBIT photons/s ions/cm 2 1 count/s

32 Detail of the trapping region FEL excitation fluorescence detection

33 Soft X-ray laser spectroscopy at FLASH FEL 50 ev beam excites resonantly the 2s-2p transition in Li-like Fe 23+ 2p 2 P 3/2 excitation by FLASH 2p 2 P 1/2 detect fluorescence 1% QED contribution 2s 2 S 1/2 Li-like ions have highest relative QED contributions to transition energy (up to 15% for U 89+ )

34 Laser bandwidth reduced by scanning monochromator E/ΔE = 2000 E/ΔE = 70

35 Resonant laser fluorescence excitation Arrival time ( s) Integral counts on MCP(E,t) right scale x c = (11)(150) ev FWHM=0.0353(24) ev Photon energy (ev) Counts S. W. Epp et al., PRL 98, (2007)

36 Soft X-ray laser spectroscopy of Li-like Fe Fluorescence (counts) /DoF = R 2 = y ±0.3 x c ± w ± A 1.16 ±0.05 preliminary results 2 /DoF = R 2 = y ± 0.5 x c ± w ± A 1.37 ± Photon energy (ev) Resolving power E/ E currently:~2600 near future: evaporative + sympathetic cooling: no limits! Accuracy: ± 6 ppm QED contributions of ppm Δ exp =( ± 0.001) ev Δ lit = ev

37 Calibrations fail at the required level of accuracy

38 QED contributions to transition energy in Li-like HCI These results test recent QED calculations at the level of: 1,2,3 virtual photons exchange between bound electrons one loop self energy + vacuum polarization self-energy screening by core electrons nuclear size effects relativistic nuclear recoil CALIBRATION STANDARDS NOT GOOD ENOUGH!

39 (A) one, (B) two and (C) three virtual photon exchange between electrons. Radiative corrections: (D) one loop SE + VP (H-like), (E) screening of (D) by core electrons, (F) nuclear size, (G) relativistic nuclear recoil. Total rel. uncertainties (right scale): (H) theory; (black squares): experiment

40 Photoionization direct PI E=h E kin + E=h resonant PI L E binding L E res K K interference Fano profiles doubly excited autoionizing

41 Photoionization of ions: extremely difficult in lab Limitations of current techniques (merged beams): HCI with ionization potentials lower than 150 ev (Ce 9+ ) low charge state ions (Ne 3+, C 2+ ) photon energies < 300 ev Most astrophysically relevant ions excluded! Ion current: ~100 na Target density: < 10 6 cm -3 Interaction time: ~ μs H. Kjeldsen, J. Phys. B 39 (2006) R325

42 Photoionization of ions Photoionization of O + as a function of photon energy for an admixture of 57% metastable and 43% ground-state O + ions Single and double ionization of Xe 4+. Discrete lines result from autoionization of Xe 4+ excited states, continuous lines from single 4d photoionization of part of the Xe 4+ and from the Auger decay of coreionized Xe 5+. (Bizeau et al.)

43 Measured and calculated cross sections for PI of C 2+ ions The solid curve represents the weighted sum of the R-matrix results assuming 60% of ground state (gs) ions in the primary beam, 30% in the 3 P 0 and 5% each in the 3 P 1 and 3 P 2 metastable (ms) states. The theoretical result is almost indistinguishable from the measurements below 51 ev... Photoionization of C 2+ ions: time-reversed recombination of C 3+ with electrons, A. Müller et al., J. Phys. B: At. Mol. Opt. Phys. 35, L137 (2002)

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45 Photoionization of ions Photoionization theory has few experimental benchmarks for HCI HCI photon opacity data are based completely on untested theory EBIT allows for systematic studies with HCI along: isoelectronic sequences, isonuclear sequences, isotopic shifts

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47 Photoionization of HCI in the EBIT - Photoionizing trapped HCI Velocity filter Soft x-ray photon beam - Extracting photoions Position-sensitive ion detector (TOF) Ion deflector BESSY 2008/09 Ion optics EBIT Electron collector Fluorescence diagnostics Trap electrodes Magnet coils Electron gun

48 Photoionization of trapped HCI

49 Photoion extraction and analysis mirror z-manipulation Wien filter & PSD electrostatic ion deflector FLASH steering lens FLASH trap trap YAG fluorescence light CCD HCIs ion optic positive ground negative voltage

50 Photoion extraction and charge analysis Fe 14+ Wien filter monochromator position sensitive detector Fe 15+ B E extracted ions photon beam: photons/s electrostatic deflector collector trap gun

51 Overlap monitoring Mirror with hole allows imaging of screen N 2 injection collector electron beam: ~3mA, 60eV trap electron beam photon beam trap 4 mm gun overlap of ions and photons: fluorescent screen 120 µm

52 Overlap monitoring horizontal beam extension: 240 μm 50 vertical beam extension (pixel) ~22.5 μm/pixel electron beam d ~ 180 μm slit width (μm)

53 Calibration runs: Photoionization Ne (He ) Intensity (counts) Data: TMETM5_F Model: Fano Weighting: y Statistical Chi^2/DoF = R^2 = q ± gammares ± Eres ± y ± A ± Data: TMETM5_F Model: Fano Weighting: y Statistical Chi^2/DoF = R^2 = q ± gammares ± Eres ± y ± A ± The use of narrow photoionization resonances of He etc. can provide calculable standards in the region up to 80 ev F J Fano fit of TMETM5_F Energy (ev) Intensity (counts) 700 Model: Fano Weighting: Statistical Chi^2/DoF = R^2 = q ± 0.04 res ± Eres ± y0 161 ± 4 A 107 ± 5 L Fano simulation residue Photon energy (ev)

54 600 Photoionizing trapped N 3+ at BESSY Ration N 4+ /N Ionisation edge N 3+ 1s 2 2s 2p 3 P Ionisation edge N 3+ 1s 2 2s 2 1 S Photon energy (ev)

55 Photoionizing trapped N 3+ at BESSY

56 N 3+ in comparison with earlier work

57 Photoionized Fe 14+ : highest charge state reported Ar 8+,10+,12+, Fe 12+,14+ also studied 34 Photoionization signal (arb. u.) Ar 8+ to Ar 9+ threshold 2s7p 2s8p 2s9p 2s10p 2s11p Photon energy (ev) ,4 447,6 447,8

58 Ar 12+ has an IP of 684 ev

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60 Fe 14+ photoionization

61 Fe 14+ photoionization Current sensitivity 20 kbarn

62 Autoionizing resonances natural linewidth 40 mev Photoion signal (counts) Lorentz fit /DoF = R 2 = 0.94 y 0 =167 ± 3 x c = ± w = ± A = 106 ± Photon energy (ev) Current resolution E/ E=6500, but monochromators reach >50000, very interesting for precision studies!

63 Agreement with RMBPT at 0.2 ev for strongest lines

64 Population of Fe 15+ in trap depends on time with photons without photons Rate: probability for photoionization per unit time per unit of photon flux: absolute cross section for photoionization! Resonance at 807 ev res = (430±260) Mbarn

65 Calculations available for Fe 14+ Magenta dots: our data Red curve: HULLAC Black curve: RMBPT Doppler shift depends on prediction (M. Gu, E. Behar) Hypothetical two-phase outflows? Our results confirm RMBPT calculations; therefore, no two-phase outflows occur in NGC 3783

66 Doppler shift corrected based on experiment Laboratory measurements of HCI absorption line positions and cross sections are possible with EBITs

67 Photon energy ranges accessed BESSY 2009: resonant photoionization approved proposal for PRL 98, (2007) FLASH EBIT proposal (2001) Bi 82+ I. Klaft et al. 5.1 ev 2. S 15+ H. Sträter et al. 2.9 ev 3. F 7+ E. Myers et al ev

68 PI range extended

69 Summary Photoionization of Fe 14+ in the X-ray region, soft X-ray laser spectroscopy (Fe 23+ ) demonstated Energies at 1 kev better than 0.1 ev (calibration limited), statistical uncertainties of 10 mev Absolute PI cross sections with less systematic error sources EBITs allow study of HCI photonic interactions in an experimentally unexplored regime

70 A brilliant outlook Higher photon energies at X-ray FELs: LCLS, X-FEL Photoionization of HCI at kev energies: Fe K shell Multiphoton processes, multiply excitations Lifetime measurements in the fs range: pump-probe HCI as atomic X-ray frequency standards

71 People involved MPIK T. Baumann, C. Beilmann, S. Bernitt, G. Brenner, F. Brunner, S. W. Epp, R. Ginzel, M. C. Simon, M. Schwarz, R. Klawitter, K. Kubicek, V. Mäckel, P. Mokler, B. L. Schmitt, JRCLU, J. Ullrich HI-LIGHT Collab. E. Behar, Technion P. Beiersdorfer, LLNL A. Rassmussen, SLAC G. Brown, LLNL DESY R. Treusch M. Kuhlmann N. Guerassimova M.V. Yurkov E. Schneidmiller J. Feldhaus J. R. Schneider Univ. Hamburg M. Wellhöfer M. Martins W. Wurth BESSY G. Reichardt O. Schwarzkopf R. Follath R. Püttner Support by Max-Planck Gesellschaft: Advanced Study Group ASG at the Center for Free Electron Lasers Physics CFEL

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73 LCLS and XFEL experiments Inner-shell photoionization of HCI can produce multiply excited states decaying through a cascade channels resonantly coupled to the nucleus Direct photoexcitation can be achieved, even multiphoton processes may be accessible Collaboration HI-LIGHT: Highly Charged Ions in the Ultrabrilliant Light of the LCLS P. Beiersdorfer et al.(llnl), J. R. Crespo López-Urrutia, J. Ullrich, et al. (MPI-K Heidelberg), S. W. Epp (MPG Advanced Study Group/CFEL), A. Müller, S. Schippers (Giessen University), R. Schuch, E. Lindroth (Stockholm University), D. W. Savin (Columbia University), S. M. Kahn (SLAC), F. Schlachter (LBNL), J. Burke, N. Scielzo (LLNL), S. Manson (University of Georgia), F. S. Porter (NASA Goddard), J. Sapirstein (Notre Dame University), L. Schweikhard (Greifswald University)

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