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Zero-degree Auger Projectile Spectrometry in the New Experimental Storage Ring: Challenges and Prospects Theo J.M. Zouros University of Crete & IESL-FORTH Heraklion, Crete SPARC-Paris, February 12-15, 2007 1 Motivation: High resolution electron spectrometry in the NESR • Auger and conversion lines of high-Z few-electron ions produced in collisions with atoms - No measurements for ions!!! (only neutral targets to date) - Charge state q-dependence – high precision Binding Energy determination of atomic levels • Physics of strong fields: - Collision dynamics, state-selective cross section determination - Atomic Structure of high-Z few-electron ions (relativistic effects) This will require electron observation in the beam direction known as Zero-degree Auger Projectile Spectroscopy (ZAPS) Of relativistic electrons with lab energies up to about 0.5 MeV Combined with a spectrometer resolution of Δp/p ≤ 10-4 access to the natural line widths Γ should also be possible The NESR: the ultimate fantasy for atomic collisions physics? NESR to FLAIR NESR ~9m • Circumference: 221.11 m • Vacuum: ≤ 10-11 mbar • Ion energies: 4 -740 MeV/u • Ion beam species: H – U • Radioactive beams: yes • Ion charge states: Α/q ≤ 2.7 • Number of ions: ~108 • Beam particle current: ~1013 #/s • Emittance: 0.1 – 1 mm-mrad • Momentum Δp/p (cooled): ≤ 10-4 Gas-jet target (extrapolation from ESR) • Areal Density: 1012-1013 #/cm2 • Length: 1.4 - 4 mm • Background pressure: 10-9 mbar Two different electron spectroscopies Zero-degree Auger Projectile e- Spectroscopy (ZAPS) • used successfully since the 1980’s primarily at Tandems to measure Auger electrons from projectiles excited via capture, excitation or ionization and combinations • emitter: low-Z HCI ions in the 0.1- 3 MeV/u collision regime • electrostatic spectrometers: lab electron energies ε = 0-6 keV and Rε= Δε/ε ~0.1% p p 1 β-ray spectroscopy • used successfully in the 1950-1970’s at high flux reactors or with radioactive sources to measure conversion and Auger electrons • emitter: stationary high-Z neutral activated target atoms • large radius (e.g. 50cm Uppsala, 100cm Chalk River, 50cm BILL) double focusing magnetic spectrometers: lab electron energies ε ≤ 3 MeV and Rp= Δp/p ~ 0.01- 0.05% The SPARC electron spectroscopy initiative is expected to combine both expertise Traditional 00 e- spectrometer two-stage 450 parallel plate with intermediate deceleration stage JPB16 (1983) 3965 Deflector Deflector Proj Ion Beam Auger Ion Beam Faraday Faraday Cup Cup GasCell Cell Gas electrons electrons Gas in Gas in Target Auger Pressure Gauge Pressure Gauge Line blending Signal Signal ΔΕ/Ε=3% Decel stage Decel stage Analyzer Analyzer • Robust operation Detector PRA31 (1985) 684 • Voltages scanned to acquire spectrum • High resolution ~0.1% uses deceleration stage with fixed pass energy Advantages of 00 Auger projectile spectrometry (ZAPS) • Only a single pre-selected Projectile charge state involved - considerable simplification of lines in spectrum – no line blending (mixture of different charge states) - “ion surgery” collisions with low-Z few-electron targets (He, H2) - very successful in isoelectronic studies • High resolution technique with relatively high overall efficiency - ΔΕ/Ε~0.1%, Δθ~10, ΔΩ~10-4 sr - Resolution good enough to resolve most K-Auger lines - Much more efficient than comparable resolution crystal X-ray spectrometers (for low-Z ions high Auger yield, no window absorption, large ΔΩ) • Determination of absolute double differential cross sections - collisional energy dependence of well defined transition • Deceleration stage provides useful variable resolution - low resolution or high resolution can be used as needed Question: How can ZAPS be done effectively in the NESR? Important features of 00 Electron emission spectrum -18 cusp ve = Vp 10 0 electron spectra -22 10 0 2p 2s 3lnl'(n>3) emission inelastic 2s 0 0 Backward 3l3l' 3l3l' -21 2 emission 10 0 180 elastic scattering 0 scattering 180 1000 1. 2. 3. 4. 5. Binary Encounter (ve = 2Vp) 10 2s Forward -20 2 DDCS (cm /eV sr) + H2 0 1s -19 10 8+ 30.04 MeV F 2000 3000 Low energy Target e- continuum Cusp e- at v = Vp High energy Projectile e- continuum Broad Binary Encounter e- Peak Kinematically shifted Auger Projectile e- lines 4000 LAB Electron Energy (eV) Kinematics: Laboratory energy Shifting and Doubling Emission from moving source Projectile electrons are shifted energetically to higher and lower laboratory energies depending on whether they are emitted in the forward (+) or backward (-) direction. For 0 0 : v Vp v' (classical ) β β' β 1pβ β' p (relativis tic) Kinematics: Instrumental Line Broadening I F. Fremont | ε(θ Δθ/2) ε(θ Δθ/2) | for θ 00 ΔE θ | ε(Δθ/2) ε(00 ) | for θ 00 For θ>00 ΔΕθ ~ Δθ, while for θ=00 ΔΕθ ~ Δθ2 thus substantial gains in resolution can be attained by going to θ=00 observation angle -4 0 p/p=10 0 Fractional kinematic Momentum Broadening B p± /p ± (x 10 -4 ) 1 0.8 0.6 = 0.1 0 0.4 Rest frame emittion angle 0.2 0 spectrometer 0 180 0.1 0.08 0.06 At 00 the kinematic broadening - grows with projectile velocity Vp - grows approximately as Δθ2 - diminishes with Auger energy ε΄ 0 ' - Rest frame Electron energy 0.04 0.02 0.01 0.008 0.006 keV ' = 1 0.004 0keV ' = 1 0.002 Kinematics: Instrumental Line Broadening II 0keV ' = 5 1E-3 8E-4 6E-4 keV 31.8 ' = 1 4E-4 4 6 8 10 20 40 60 80100 200 400 600 Projectile energy [MeV/u] Range in spectrometer acceptance angle Δθ 2nd order fractional momentum broadening : ΔB p ΔB p p p V Δθ 2 p 8 v' β | 1 β β' | Δθ 2 p p 8 β' (1 - β 2 ) p (classical ) ΔΒp+/p+ = 10-4 (relativis tic) Δθ (dgrs) ΔΩ (10-4 sr) ε΄=1keV ε΄=131keV 4 MeV/u 740 MeV/u 4 MeV/u 740 MeV/u 1.35 5.55 0.25 0.19 4.15 52.5 0.65 1.29 Comparison of Tandem - NESR Typical Beam and Target operational parameters Target density n (1013 #/cm2) Target Length L (cm) nL (1013#/cm2) Charge State q Beam Current Ip=Iq/qe (1010#/s) Ip n L (1025 #/cm2s) Tandem 160 (50mTorr) 5 800 1-10 0.6-60 4.8-480 NESR 16* (5mTorr) 0.1-0.4 1.6 - 6.4 A/q ≤ 2.7 238U89-92+ 1250 11000** 20 -700 *projected from experience with ESR jet target ** Assuming a constant 108 particles in the NESR over the 4-740 MeV/u energy range and for q=92 NESR advantages (+) vs disadvantages (-) (+) High particle current, increases with collision energy (-) jet target: smaller density and effective length (but note Grisenti talk on liquid targets) Question: Possibility of cell target? Would increase rate by at least x500! The Univ. of Crete ZAPS spectrometer At Kansas State U. Technical developments: 2-D PSD with 4-element lens + doubly differentially pumped gas cell Turbo pump Faraday Cup Ion Beam 4-element lens Gas Cell Gas in Pressure Gauge • PSD: x 100 -700 higher sensitivity • ΔE acceptance ~ 20% • 4-element lens for deceleration and focusing • Resolution ~ 0.05-0.1% • ΔΩ = 1.8 x 10-4 sr (Δθ = 0.8680) electrons PSD-RAE X-Position Y- Position Timing β – ray spectroscopy Conversion lines Bz r Bz ~ 1 / r Dedicated machines requiring huge housing To ensure field uniformity and easy access 50cm 1/r BILL electron iron-core spectrometer Natural width Γp/p=1x10-5 Slit widths: Entry = s1 Exit = s2 s1=s2 = 0.2 mm 0.5% energy ρ =50 cm Best resolution Δp/p = 7.6 x 10-5 Bz ~ 1 / r 0.05% energy Bz ~ 1 / r Envisioned two-stage magnetic spectrometer Use in storage rings: The (original ESR proposal Rido Mann et al 1988 – GSI) μ – metal shielding/ Helmholtz coils? ultimate ZAPS? • Ultimate resolution: δp/p < 10-4 • Lab e- energy: 3-500 keV 1st stage (deflector) • low dispersion, low resolution • uniform field dipole • target spot size 1mm x 1mm • large angular acceptance 5-100 2nd stage • high dispersion, high resolution • r-n Bz-field (n=1 BILL, n=2 Chalk River) • entry slit widths ~0.1-1 mm small angular acceptance 0.1-0.50 • 2-D PSD Γ΄=100eV, ε΄=80keV, Δθ=0.20 (full-acceptance) Resolution contributions Projectile Δp/p = 5 x 10-5, Spectrometer Δp/p = 1 x 10-4 4 MeV/u 200 MeV/u 740 MeV/u Lab width Γ (eV) 118.895 258.73 476.01 Kinematic Broadening (eV) 0.0593 2.0875 15.267 Projectile-energy Spread (eV) 1.6310 21.805 58.677 Spectrometer ΔΕ (eV) 20.066 63.963 132.92 Conclusions Important technical issues to take into consideration/resolve: • Iron or Air -core magnet design? - Air-core seems better but needs more space! - Iron -core: problem of magnetic field uniformity over 1 m radius? problem of Remanent magnetization? • Solid angle considerations - small Δθ~0.10 (to limit kinematic broadening for line width measurements) will severely limit count rate – PSD necessary • Good design, optical alignment and slit/baffle controls will be critical • High quality non-magnetic materials to be used in the entire target area • Need for highest areal density target (liquid H2/He)? • At the 10-5 precision level - Earth magnetic field annulment (μ-metal shielding/large Helmholtz coils?) - Temperature stability to ~0.10 C Anybody up to the challenge? Come join the SPARC electron spectroscopy group! http://www.gsi.de/fair/experiments/sparc/electron-spectrometers_e.html Bibliography • N. Stolterfoht, Phys. Rep. 146 (1987) 315-424. • T.J.M. Zouros and D.H. Lee, in Accelerator -Based Atomic Physics Techniques and Applications, ed. S. Shafroth and J.C. Austin, AIP, Chapter 13 (1997) p. 427-479. • E.P. Benis et al. Phys. Rev. A 69 (2004) 052718. • W. Mampe et al., NIM 154 (1978) 127-149. • R.L. Graham, G.T. Ewan and J.S. Geiger, NIM 9 (1960) 245-286. For more information also check my home page: http://www.physics.uoc.gr/~tzouros XX International Symposium on Ion-Atom collisions* and SPARC topical meeting on Electron spectrometry in the NESR August 1-4, 2007 Agios Nikolaos, Crete, GREECE *a satellite of XXV ICPEAC - Freiburg Resolution contributions Γ΄=10eV, ε΄=50keV, Δθ=0.20 (full-acceptance) Projectile Δp/p = 5 x 10-5 , Spectrometer Δp/p = 1 x 10-4 4 MeV/u 200 MeV/u 740 MeV/u Lab width Γ (eV) 12.291 28.857 54.048 Kinematic Broadening (eV) 0.04942 2.0248 15.347 Projectile-energy Spread (eV) 1.3143 18.963 51.949 Spectrometer ΔΕ (eV) 13.844 53.065 115.84 Resolution contributions Γ΄=10eV, ε΄=1keV, Δθ=0.20 (full-acceptance) Projectile Δp/p = 5 x 10-5 , Spectrometer Δp/p = 1 x 10-4 4 MeV/u 200 MeV/u 740 MeV/u Lab width Γ (eV) 24.894 122.53 256.45 Kinematic Broadening (eV) 0.0280 5.0441 47.754 Projectile-energy Spread (eV) 0.3678 11.124 34.056 Spectrometer ΔΕ (eV) 1.2258 23.851 69.620 Kinematics: energy shifting and doubling II - Projectile Rest frame e energies ' 0 0: 0 180 : 0 ± - 0 laboratory electron energies (keV) 1000 800 600 400 U 91+ 1 keV 10 keV 50 keV 1 keV 10 keV 50 keV 131.8 keV 131.8 keV 1000 800 600 I.P. 131.8keV 400 200 200 100 80 60 40 100 80 60 40 20 20 10 8 6 4 10 8 6 4 2 2 1 0.8 0.6 0.4 Vp=v' Vp=v' 1 0.8 0.6 Vp=v' 0.4 0.2 0.2 0.1 0.1 4 6 8 10 20 40 60 80 100 200 Projectile energy [MeV/u] (NESR range) 400 600 For He-like Uranium K-Auger series energies (75 -130 keV rest) frame Range in Lab from about 100 - 1000 keV (+) 40 - 0 keV (-) For projectile energies 4 -740 MeV/u Angular compression – “beaming” θmax 80 For Vp / v' 1 (β p /β' 1) there is 60 ε΄=75000eV a maximum lab observatio n angle θ max : ε΄=131800eV 40 θ max Arc sin[ 20 ' ' ] p p ε΄=10000eV ε΄=1000eV 100 200 300 MeV/u 400 500 600 700 At 740 MeV/u we have: For ε΄=1000 eV, θmax = 2.4070 ε΄= 10 eV, θmax = 0.240 Strong beaming for small electron energies Practically total cross section measured around 00 All differential information averaged out β β΄ θmax βp Kinematics: Line stretching and enhancing PE=7 eV Ranal=3% Natural Line widths Γ’ (rest frame) are Changed to widths Γ± in Lab frame 00 Kinematic Line Stretching or Compressin g : (- only for β p β' ) Γ p | Γ 'p' | (classical - no stretching ) Γ p γ p | β pβ'1 | Γ 'p' (relativis tic - mild stretching ) Momentum Kinematic Line Enhancemen t d 2σ d 2 σ' dpdΩ θ 00 dp' dΩ' (classical - No!) d 2σ γ d 2 σ' d 2 σ' γ p (1 β pβ' ) (relativis tic) dpdΩ θ 00 γ' dp' dΩ' dp' dΩ' Energy Kinematic Line Enhancemen t Vp v' d 2 σ' d 2σ dεdΩ θ 00 v' dε' dΩ' (classical - yes! ) (β p β' ) d 2 σ' d 2σ p d 2 σ' γp (relativis tic) dεdΩ θ 00 p' dε' dΩ' β' dε' dΩ' Mild enhancement and stretching in momentum analysis!! Kinematic Widths and Enhancement factors Krause 1968 Lab widths K-level natural line widths p momentum (eV/c) and energy (eV) Momentum widths are stretched only weakly While energy widths a lot! 3000 '=100 eV 2000 1 keV 75 keV 131.8 keV 900 800 700 600 500 400 300 200 For atoms K line-widths dominated by Radiative widths at high Z And Auger widths at low Z What about Highly Charged Ions? p - momentum - energy 90 0 100 200 300 400 500 Projectile energy (MeV/u) 600 700 Zero-degree Auger Projectile electron spectra Elastic scattering on B4+ and B3+ ESM ESM R-matrix R-matrix