Electron-driven resonant processes Recom bination processes e beam - PowerPoint PPT Presentation

Electron-driven resonant processes

Recom bination processes e beam Dielectronic recombination DR resonant two-step process: • capture of a free electron and bound t n= ∞ electron excitation. E 1 • radiative stabilization via photon em ission . n=2 E γ E 2 e beam E γ n=1 n= ∞ E 1 Radiative recombination RR n=2 non-resonant process • capture of a free electron with photon • em ission E 2   n=1         q q 1 A e A RR

Dielectronic recombination Dielectronic recombination       * *            q q 1 q 1 * A e A A E beam Resonance condition:  RR E b +E 2l =E 1s -E 2l photon: E  ~E 1s -E 2l E B 2p 2s  DR Radiative recombination Radiative recombination 1s   E E E  beam Binding           q q 1 A e A

The bare uranium signal U 9 2 + at SuperEBI T 10 U 92+ ions trapped!

Photorecom bination of Hg 7 2 + bis Hg 7 8 + at 7 2 .5 keV electron beam energy n=3 400 20 ion abundance (%) 15 Hg K  10 n=4 Intensity 5 Hg K  0 69 70 71 72 73 74 75 76 77 78 200 Hg ion charge state n=5 n=2 n=2 j=1/2 j=3/2 0 65 70 75 80 85 90 95 100 105 Photon energy (keV)

X-ray data depending on electron energy 7 10 Fe 24+. Fe 18+...24+ ions are 4 6 10 Fe 23+. Breeding time (s) sequentially 5 Fe 22+. 10 3 generated interaction time 4 Fe 21+. 10 3 Fe 20+. 10 2 Fe 19+. 2 10 Fe 18+. 1 1 10 0 10 0 4500 4500 4600 4600 4700 4700 4800 4800 4900 4900 5000 5000 5100 5100 5200 5200 5300 5300 Electron beam energy (eV) Electron beam energy (eV) Ions in any desired charge state can be prepared, stored and spectroscopically studied

Tuning the electron energy Experiment: • vary electron beam energy (x-coordinate) • measure photon energy (y-coordinate) RR: as the electron beam energy changes:  Photon energy shifts continuosly DR: as the electron beam energy changes:  characteristic dielectronic resonances  selectively excited lines

Radiative and dielectronic recom bination He-like Ar 1 6 + 4 0 0 0 Photon energy ( eV) 4  1 3  1 n= 2  n= 1 direct excitation 3 0 0 0 DR resonances 2 2 0 0 3 2 0 0 Electron beam energy ( eV)

51 Measurement technique : DR

Typical DR spectrum RR n=2 RR n=3 RR n=4 52

Typical DR spectrum n = 4-1 DR n = 3-1 DR n = 2-1 DR KLL KLN KLO…. DE KLM 53

Dielectronic recom bination resonances w ith high resolution 1e QED 4 eV 2e QED 0.2 eV recoil 0.08 eV 0.04 eV uncertainty -Fe helium-like and lithium- like ions studied with electrons -X rays detected also with a high resolution crystal spectrometer

Dielectronic recom bination resonances w ith Hg 7 7 + Hg, Li-like Hg +77

Zoom into the KLL resonances of different isoelectronic sequences of Hg ions Hg, Li-like Hg +77 The element names mean the corresponding isoelectronic sequence, e. g., Be-like: four electrons left, thus Hg 76+

The KLL resonances KL 1 / 2 L 1 / 2 KL 1 / 2 L 3 / 2 2p 3/2 2p 3/2 2s 1/2 2s 1/2 2p 1/2 2p 1/2 Be-like  B-like 1s 1s and analogously the KL 3 / 2 L 3 / 2

Quantum interference betw een DR and RR DR final state initial state ? + + RR Fano profile González et al., Phys. Rev. Lett. 9 4 , 203201 (2005)

Asym m etry due to quantum interference

QED scales w ith Z 4 only a few eV accuracy needed since effects are very large

More complex even: trielectronic and quadruelectronic recombination •Resonant many-electron excitations contribute far more to electronic recombination and Auger decay than expected. •This affects radiative energy transfer in stars.

Dielectronic recombination Prominent Higher-Order Contributions to Electronic Recombination, C. Beilmann et al., PRL 107, 143201 (2011)

Trielectronic and quadruelectronic contributions to resonant photorecom bination • At Z<18, trielectronic processes (TR) dominate the resonant recombination, even though the number of electrons involved is higher and the process of higher order

X-ray data depending on electron energy Fe photorecombination studies • Slow scans at high electron energy resolution •

Unexpected, strong contributions by many-electron resonant excitation at high resolution C. Shah et al., Phys. Rev. E 93 93, 061201(R) (2016) C. Beilmann et al., Phys. Rev. Lett 107 107, 143201 (2011) C. Beilmann et al., Phys. Rev. A 88 88, 062706 (2013)

Unexpected, strong contributions by many-electron resonant excitation at high resolution C. Shah et al., Phys. Rev. E 93 93, 061201(R) (2016) C. Beilmann et al., Phys. Rev. Lett 107 107, 143201 (2011) C. Beilmann et al., Phys. Rev. A 88 88, 062706 (2013)

LM n region of tungsten 13000 12500 12000 11500 11000 Photon energy (eV) 10500 10000 9500 9000 8500 8000 7500 7000 6500 6000 6500 7000 7500 8000 8500 9000 9500 Electron energy (eV)

LMn region of tungsten 20000 15000 Counts 10000 5000 0 6500 7000 7500 8000 8500 9000 9500 Electron energy (eV)

Photoionization of HCI • Photoionization theory has few experimental benchmarks for HCI • HCI photon opacity data are based largely on untested theory • EBIT allows for systematic studies with HCI along isoelectronic and isonuclear sequences,

Photoion extraction and charge analysis Fe 14+ monochromator Wien filter Fe 15+ extracted ions B photon beam: position 10 13 photons/s sensitive E detector electrostatic deflector X-ray detector collector After an interaction time, ions trap and photoions are extracted, mass selected and detected gun

Photoionizing trapped N 3+ at BESSY EBIT electron beam has to operate below ionization threshold!

Fe 14+ photoionization M. C. Simon et al., Phys. Rev. Lett. 105 105 (2010) 183001

Fe 14+ photoionization Strong resonances Current sensitivity for non- allow high resolution resonant photoionization nearly reaching around 20 kbarn natural line width

Agrees with RMBPT (Gu) at 0.2 eV level For these ions, HULLAC (A) has errors of few eV, but older work, e. g., TOPbase typically 10 eV and more!

Doppler shift corrected based on experiment 0 - 1 1 5 . 0 1 5 . 5 1 6 . 0 1 6 . 5 1 7 . 0 1 7 . 5 Precise measurements of HCI X-ray absorption line positions and cross sections are possible with EBITs

Optical spectroscopy with EBITs

Optical spectroscopy with EBITs • No reports about HCI of interest, and no transition data available for most HCI: Spectral desert • HCI production in EBIT easy, identification much harder Color 80 950 Grey: 75 scale: 512 70 Ionic charge state + 1 no lines reported Number 65 256 60 of known 128 55 50 transitions 64 45 Iridium HCI 32 40 35 16 30 25 8 20 4 15 10 2 5 1 50 55 60 65 70 75 80 Atomic number Z

Spectroscopy of few-electron ions in the visible range electron Grating spectrometer with gun cryogenically cooled CCD trap CCD spectrometer SC magnet imaging optics collector

Hyperfine structure of the H-like ions Ground state energy splitting  for an H-like ion scales with Z 3 Dirac terms       4 3 2 Z m I j m c                 I e e A 1 ( 1 )       rad 3 n I m j ( j 1 ) 2 l 1 p Z=1 Z=67 =67 (Ho) (Ho)  6  eV 2 eV Lifetime 11.000.000 years 5 ms  : Breit-Rosenthal effect (8 %)  nuclear charge distribution  : Bohr-Weißkopf effect (2 %)  nuclear magnetization distribution  rad : QED contributions (0.5 %)  vacuum polarization, self energy  QED & nuclear structure

Hyperfine splitting for heavy hydrogen-like ions EBIT EBIT GSI storage ring: LLNL LLNL Klaft et al., PRL 73, 73, 2425 (1994) ESR ESR Seelig et al., PRL 81 4824 (1998) GSI GSI Pb 81+  HFS = 572.64 nm 165 Ho 66+ JRCLU, P. Beiersdorfer, D. W. Savin, and K. Widmann, PRL 77 77, 826 (1996)  HFS = 451.58, 455.92 nm 187,185 Re 74+ JRCLU, P. Beiersdorfer, B. B. Birkett, K. Widmann, A.-M. Mårtensson-Pendrill and M. G. H. Gustavsson, PRA 57 57, 879 (1998)  HFS = 385.82, 382.18 nm 203,205 Tl 80+ P. Beiersdorfer, S. B. Utter, K. L.Wong, JRCLU, J. A. Britten, H. Chen, C. L. Harris, R. S. Thoe, D. B. Thorn and E. Träbert, M. G. H. Gustavsson, C. Forssén and A.-M. Mårtensson-Pendrill, PRA 64, 64, 032506 (2001)

Extremely low systematic frequency shifts Estimates for systematic frequency shifts in hydrogen-like ions are extremely low: excellent optical clocks possible. Hydrogenlike Highly Charged Ions for Tests of the Time Independence of Fundamental Constants, S. Schiller, PRL 98, 98, 180801 (2007)

Our trapped highly charged ions are too hot Laser spectroscopy with HCI suffers from the deep trapping potential in an EBIT: high ion temperature fluorescence imaging tunable excitation laser Resolution many orders of magnitude worse than in “normal” atomic physics laser spectroscopy

Laser spectroscopy of forbidden M1 lines Evaporative cooling Ar 13+ 3 10 5 K ion temperature V. Mäckel, et al., PRL 107, 143002 (2011), K. Schnorr et al., ApJ 776, 121 (2013)