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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 fromhighly charged ions Theo J.M. Zouros University of Crete – Heraklion GREECE KSU August 27, 2003
Crete The Mediterranean CIA map
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
Crete Heraklion
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
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
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
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!
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
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
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
Electron-ion scattering two-amplitude formula e- VS short range potential Ion +q r R Rutherford Interference Short-range
Sum of Rutherford and Short Range amplitudes Griffin & Pinzola PRA42 (1990) 248
Elastic scattering: Rutherford term Non resonant scattering Binary Encounter Peak
Elastic scattering: Rutherford & Short-range Resonant contributions
Elastic scattering: All 3 terms Resonant contributions
Elastic scattering: Sum of 3 terms Sum of resonant,non-resonant and interference contributions
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!)
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
Elastic scattering Ecm=20.69eV e- + Xe6+ Hartree-Fock Rutherford Differential electron scattering e- beam Ion beam J. Phys. B29 (1996) 4443
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
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
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
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???
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
----- 2s2p 3P ----- 2s2p 1P Elastic scattering of quasi-free electrons on B3+ ions Doubly Excited states Zouros et al PRA 2003 RC
First Z-dependence study of a triply-excited state Benis et al JPBL submitted 2003
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!)
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??!!
Comparison of Compton Profiles Li vapor target H2 target
The EndMany thanks to all my colleagues and friends for making my sabbatical such a fun and exciting experience!
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!!!
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)
1s2s 3S Metastable fraction Foil stripping Gas stripping
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
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
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 !
Elastic scattering of quasi-free electrons on B3+ ions Triply Excited States
f =5% f =25% B3+ (1s2s 3S) → B3+ (2s2p 3P) → B4+ (1s) + eA
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)
e- q Ion e- v q V Ion Scattering of free electrons on HCI Scattering of quasi-free electrons on HCI Atom
Compton Profiles x |F(p)|2 z y = probability to find e- with component pz
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!!