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Quasi -free electron scattering from highly charged ions

Quasi -free electron scattering from highly charged ions. Theo J.M. Zouros University of Crete – Heraklion GREECE. Crete. The Mediterranean. CIA map. Heraklion. 50 km. 250 km. The island of Crete. Area ~ 8200 km 2 (3200 mi 2 ) Population ~ 600 000 winter

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Quasi -free electron scattering from highly charged ions

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  1. Quasi-free electron scattering fromhighly charged ions Theo J.M. Zouros University of Crete – Heraklion GREECE KSU August 27, 2003

  2. Crete The Mediterranean CIA map

  3. Heraklion 50 km 250 km The island of Crete Area ~ 8200 km2 (3200 mi2) Population ~ 600 000 winter > 1 000 000 summer Two mountains ~ 2450 m Heraklion population ~ 220 000

  4. Crete Heraklion

  5. University of Crete - Heraklion University Hospital Physics Dept UoC campus Physics & Biology Medical school From my living room UoC ~ 5000 students Physics Dept ~ 600 under grads 50 grads 30 faculty

  6. Recent collaborators J.R. Macdonald Lab Kansas State Univ. Dr. Manolis Benis PhD 2001 Univ. of Crete & JRM Prof. Tom Gorczyca Western Michigan Univ. R-matrix calculations Prof. Pat Richard Prof. (Emeritus) Chander Bhalla Pierre Auger 1899-1993 Auger effect 1923-1925 Teck Lee Grad Student Mikhail Zamkov Grad Student

  7. Ion – atom/electron collisions t = -∞ ∆t = 10-17 s t = -∞ Preparation Interaction Relaxation Ionization Excitation Transfer combinations e- Non radiative: Auger electrons Radiative: Photon decay Atom/Molecule Target q = 0 (neutral) Gas/Solid gs or excited state n ~ 1012-1020 #/cm3 e- e- beam Target q = -1 I ~ 1-50 μA n ~ 106-108 #/cm3 γ e- Ion beam Z ~ 1-12 I ~ 1-100 nA q ~ 1-12 E ~ 0.5-2 MeV/u V ~ 3-6 a.u. gs or metastable Detectors projectile, recoil, photon, electron coincidences ΔΩ – solid angle ε - efficiency Black box?! γ

  8. Ion-atom/electron interactions: Investigation of the Coulomb force • Force is Coulomb: • Potential usually known - can write down a Hamiltonian • Calculate emission or interaction cross sections • Difficulties: many particles, long range force, correlation effects • Model calculations • Develop theoretical and experimental techniques • Test approximations Mature field – more than 40 years old – negative population growth!

  9. Interest in ion-electron/atom collisions Applications • Tokomak and AstrophysicalPlasmas • Accelerator technology - Storage rings • Radiation damage – cancer therapy • Basic atomic collisions • Use HCI and simple targets – few-electron systems • Study ion excitation rather than target excitation: • Control charge state q of ion –Nnumber of electrons • Isoelectronic sequence study – same N different Z Recent review:Electron-Ion scattering, I. Williams, Rep. Prog. Phys. 62 (1999) 1431

  10. Presentation Summary • Resonant electron scattering (RES) • Long range – short range potential treatment • Electron – ion collision techniques • Impulse Approximation – Electron scattering model • Advantages of quasi-free electron scattering • RES applications: He-like and H-like ions, triply excited states isoelectronic sequence study • Future plans

  11. Aq-1+  En Aq-1+ (quasi-)free electron Ee E1   h Bn En En E0 E1 E1 Aq+ E1-E0  E0 E0 doubly-excited intermediate state RTE En E1 E0 radiative stabilization recombination DR or RTEX Electron - ion collisions: Production and decay of doubly excited states Aq+ capture of a (quasi-) free electron + excitation inverse autoionization autoionization Resonant electron scattering RES or RTEA Ee + Bn = E1-E0

  12. Electron-ion scattering two-amplitude formula e- VS short range potential Ion +q r R Rutherford Interference Short-range

  13. Sum of Rutherford and Short Range amplitudes Griffin & Pinzola PRA42 (1990) 248

  14. Elastic scattering: Rutherford term Non resonant scattering Binary Encounter Peak

  15. Elastic scattering: Rutherford & Short-range Resonant contributions

  16. Elastic scattering: All 3 terms Resonant contributions

  17. Elastic scattering: Sum of 3 terms Sum of resonant,non-resonant and interference contributions

  18. R-matrix results e- + B3+ (1s2)  [B2+ (1s2l2l')]  B3+ (1s2) + e- Differential scattering at large angles provides the most stringent tests of theory (all terms!)

  19. Merged beam experiments at storage ring 16O7+ H-like Eion = 8.9 MeV/u Ee=8-9keV Eecm=500 eV ΔEecm=±0.6 eV Iion= 4 E7 ion stack 7 min Kilgus et al PRL 1990

  20. Elastic scattering Ecm=20.69eV e- + Xe6+ Hartree-Fock Rutherford Differential electron scattering e- beam Ion beam J. Phys. B29 (1996) 4443

  21. UoC HEMISPHERICAL ANALYZER WITH 2-D PSD 0o ELECTRON SPECTROMETER Faraday Cup Ion Beam 4-element lens Inner hemisphere Gas Cell Pressure Gauge Gas in electrons PSD X-Position Y- Position Timing Outer hemisphere e- θ Resolution ~ 0.1% ΔΩ = 1.8 x 10-4 sr 00 dgrs Ion

  22. Experimental setup at J R Macdonald Laboratory

  23. Compton Profile J(vz) Atom v e- Vp Ion vz Z-axis Vp+vz Electron Scattering Model/Impulse Approximation Free e--Ion  Bound e--Ion Vp>>v

  24. Sliding the Compton profile across the resonances RES Εe = ΔΕ Compton profile Changing the ion velocity Vp slides the Compton profile across the doubly-excited states bringing them into resonance! Auger decay RES ΔΕ Ee =184 eV (4.0 MeV) Ee

  25. Comparison of signal ratesR (#/s) = NI ne L σ

  26. What’s the use of a quasi-free electron? • >106higher luminositycompared to • crossed electron-ion beam experiments! • Measure scattering at 1800 (very sensitive)! • Include also resonances • (e- energy dependence – d2/dEd)! • No UHV • Spectrum in 30 minutes! Sounds great but is it really electron-ion scattering???

  27. Elastic scattering of quasi-free electrons on B4+ ions Elastic scattering of quasi-free electrons on B4+ ions Doubly Excited states Zouros et al PRA 2003 RC

  28. ----- 2s2p 3P ----- 2s2p 1P Elastic scattering of quasi-free electrons on B3+ ions Doubly Excited states Zouros et al PRA 2003 RC

  29. First Z-dependence study of a triply-excited state Benis et al JPBL submitted 2003

  30. quasi-free electron scattering provides the only way to presently observe differential RES! (particularly at the large scattering angles) Summary and Conclusion • Large-angle differential electron – ion scattering provides some of the most stringent tests of both atomic structure and collision dynamics • State-of-the-art DDCS calculations (R-matrix) for free electron • scattering from He-like and H-like ions are in excellent agreement with • quasi-free electron experiments involving ion-H2 collisions over a wide • energy region and many resonances quasi-free electron scattering is real electron scattering! (remember Compton scattering – electrons there also really quasi-free!)

  31. Future • Improve apparatus – add first stage and double differential target • Use Li vapor target that has narrower Compton profile – (Laser-excited) Rydberg Li target? • Expand studies to include: many electron targets higher Z ions or L shells • Incorporate zero-degree electron spectrometer system in a storage ring??!!

  32. Comparison of Compton Profiles Li vapor target H2 target

  33. H2 target

  34. He target

  35. Ar target

  36. The EndMany thanks to all my colleagues and friends for making my sabbatical such a fun and exciting experience!

  37. Summary and conclusions • 1800 Elastic e--Ion Scattering measurements • First differential observation of RES for He-like ions • First isoelectronic sequence study of triply-excited state • R-matrix calculations • Overall good agreement with the measurements • ESM seems to be a very good approximation • Quasi-free e- scattering provides unique data: • Not impaired by broad Compton profile!!! • No problem with convolution of Compton profile!!!

  38. Determination of the metastable 1s2s 3S fraction Method 1s2 1S → 1s2p2 2D[RTE] 1s2s 3S →1s2s2p 4P[Capture] Two successive measurements at the same production energy E.P. Benis et al, PRA 65, 064701 (2002)

  39. 1s2s 3S Metastable fraction Foil stripping Gas stripping

  40. e- scattering on ion |bj>=|ajLjMLjSjMSj> kili De e- kflf q DEi DEf LSP DEi DEf bf Ion+e- De bi Ion Ion Energy conservation: De=0 LS-coupling: total DL=DS=DML=DMS=DP=0

  41. B4+(1s) + H2 Absolute doubly differential cross section determination Determine the overall efficiency: Use BEe/elastic non-resonant scattering peak Determine the metastable fraction: Use capture to RTE lines ratio B3+(1s2 1S, 1s2s 3S) + H2

  42. Elastic scattering of quasi-free electrons on B3+ ions 2s2p2 2D 1s2p 3P RTEA 1s2s 3S M. Zamkov et al. Phys. Rev A 65, 032705 (2002) E.P. Benis et al, in XXI ICPEAC, Sendai, Japan, p. 505 (1999) Triply Excited States !

  43. Elastic scattering of quasi-free electrons on B3+ ions Triply Excited States

  44. f =5% f =25% B3+ (1s2s 3S) → B3+ (2s2p 3P) → B4+ (1s) + eA

  45. Non-Resonant Transfer Excitation (NTE) Uncorrelated Transfer Excitation (UTE) V V T T P P Elastic scattering of quasi-free electrons on ions(more open channels)

  46. e- q Ion e- v q V Ion Scattering of free electrons on HCI Scattering of quasi-free electrons on HCI Atom

  47. Compton Profiles x |F(p)|2 z y = probability to find e- with component pz

  48. 70 eV e- + Li+: 1 1S 2 3P Griffin & Pinzola PRA90 Highest Sensitivity at large-angle scattering d/d: 70 eV e- + Li+ 1 1S 2 3P DW: Distorted Wave UDW:Unitarized DW CC5: 5-state close coupling CC11: 11-state close coupling Largest differences between theories at 1800!!

  49. Resolution dependence study

  50. Electron scattering processes

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