SPARC-Paris, February 12-15, 2007

1

ZeroZero-degree Auger Projectile Spectrometry -degree Auger Projectile Spectrometry in the in the New Experimental Storage Ring:New Experimental Storage Ring:

Challenges and ProspectsChallenges and Prospects

Theo J.M. ZourosTheo J.M. ZourosUniversity of Crete & IESL-FORTH University of Crete & IESL-FORTH

Heraklion, CreteHeraklion, Crete

Motivation: High resolution electron spectrometry in the NESRMotivation: 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 directionelectron observation in the beam direction known as Zero-degree Auger Projectile Spectroscopy (ZAPS)Of relativistic electrons with lab energies up to about 0.5 MeVCombined 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? The NESR: the ultimate fantasy for atomic collisions physics?

NESR

to FLAIR

NESRNESR• 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 targetGas-jet target ((extrapolation from ESR)extrapolation from ESR)

• Areal Density: 1012-1013 #/cm2

• Length: 1.4 - 4 mm• Background pressure: 10-9 mbar

~ 9 m

Two different electron Two different electron spectroscopiesspectroscopiesZero-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%

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

1p

p

TraditionalTraditional 0000 e e-- spectrometer spectrometer two-stage 45two-stage 4500 parallel plate with intermediate deceleration stage parallel plate with intermediate deceleration stage

Ion Beam

Gas Cell

Faraday Cup

Deflector

electrons

Decel stagePressure GaugeGas in

Signal

Analyzer

Detector• Robust operationRobust operation • Voltages scanned to acquire spectrumVoltages scanned to acquire spectrum• High resolution ~0.1% uses deceleration stage with fixed pass energyHigh resolution ~0.1% uses deceleration stage with fixed pass energy

ΔΕ/Ε=3%

Ion Beam

Gas Cell

Faraday Cup

Deflector

electrons

Decel stagePressure GaugeGas in

Signal

Analyzer

JPB16 (1983) 3965

PRA31 (1985) 684

TargetAuger

Lineblending

ProjAuger

Advantages of 0Advantages of 000 Auger projectile spectrometry (ZAPS) 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

Question: How can ZAPS be done effectively in the NESR?

• 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

0 1000 2000 3000 4000

10-22

10-21

10-20

10-19

10-18

00

inelastic scattering

Bin

ary

Enco

unte

r

(

v e =

2V p)

1800

elastic scattering

1800

3l3

l' 2

s

3ln

l'(n>

3)

2s

cu

sp

v e =

Vp

3l3

l' 2

s

2p2

1

s

30.04 MeV F8+

+ H2

00 electron spectra

DD

CS

(cm

2 /eV

sr)

LAB Electron Energy (eV)

Important features of Important features of 0000 Electron emission spectrum Electron emission spectrum

1. Low energy Target e- continuum2. Cusp e- at v = Vp

3. High energy Projectile e- continuum4. Broad Binary Encounter e- Peak5. Kinematically shifted Auger Projectile e- lines

Kinematics: Laboratory energy Shifting and DoublingKinematics: Laboratory energy Shifting and Doubling Projectile electrons are shiftedenergetically to higher and lower laboratory energies depending on whether they are emitted in the forward (+) or backward (-) direction.

tic)(relativis β

)(classical v'V v

:0For

β'β1

β'β

p

p

p

0

Emission from moving source

Backward

emission

Forward

emission

F. Fremont

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

Kinematics: Kinematics: Instrumental Line Broadening IInstrumental Line Broadening I

00

θ

0

0θfor |)ε(0ε(Δθ/2)|

ΔE

0θfor |Δθ/2)ε(θΔθ/2)ε(θ|

Kinematics: Kinematics: Instrumental Line Broadening IIInstrumental Line Broadening II

4 6 8 10 20 40 60 80100 200 400 6004E-46E-48E-41E-3

0.002

0.0040.0060.0080.01

0.02

0.040.060.080.1

0.2

0.40.60.8

1

Rest frameemittion angle

00

1800

Bp±/p

± (x

10-4)

Projectile energy [MeV/u]

spectrometer

= 0.10

00 Fractional kinematic Momentum Broadening

' - Rest frame Electron energy

p/p=10-4

tic)(relativis )2

pβ-(1

|β'p

β1|

β'p

β

8

2Δθ

pp

ΔB

)(classical v'p

V

8

2Δθ

pp

ΔB

:broadening momentum fractionalorder 2nd

At 00 the kinematic broadening - grows with projectile velocity Vp

- grows approximately as Δθ2

- diminishes with Auger energy ε΄

4.15

52.5

4

MeV/u

ε΄=131keV

0.65

1.29

0.25

0.19

1.35

5.55

Δθ (dgrs)ΔΩ (10-4 sr)

740 MeV/u

740 MeV/u

4

MeV/u

ε΄=1keVΔΒp+/p+ = 10-4

Range in spectrometer acceptance angle Δθ

Comparison of Tandem - NESRComparison of Tandem - NESRTypical Beam and Target operational parametersTypical Beam and Target operational parameters

Target

density

n

(1013 #/cm2)

Target

Length

L

(cm)

n L

(1013#/cm2)

Charge

State

q

Beam

Current

Ip=Iq/qe

(1010#/s)

Ip n L

(1025 #/cm2s)

TandemTandem 160

(50mTorr)

5 800 1-10 0.6-60 4.8-480

NESRNESR 16*

(5mTorr)

0.1-0.4 1.6 - 6.4 A/q ≤ 2.7238U89-92+

1250 -11000**

20 -700

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)(but note Grisenti talk on liquid targets)

Question: Possibility of cell target? Would increase rate by at least x500!

*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

Ion Beam

Gas in Pressure Gauge

Gas Cell

PSD-RAEX-PositionY- Position

Timing

4-element lens

Faraday Cup

electrons

• 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)

Technical developments:Technical developments: 2-D PSD with 4-element lens +2-D PSD with 4-element lens +

doublydoubly differentially pumped gas cell differentially pumped gas cell

The Univ. of Crete The Univ. of Crete ZAPS spectrometerZAPS spectrometerAt Kansas State U.At Kansas State U.

Turbo pump

Dedicated machines requiring huge housingTo ensure field uniformity and easy access

β – β – ray spectroscopyray spectroscopy

rBz /1~

Conversion lines

Bz

r

5050cm 1/r BILL electron cm 1/r BILL electron iron-core spectrometeriron-core spectrometer

rBz /1~

Natural widthΓp/p=1x10-5

Slit widths:Entry = s1

Exit = s2

s1=s2 = 0.2 mm

ρ =50 cm

Best resolution Δp/p = 7.6 x 10-5

rBz /1~

0.05% energy

0.5% energy

Use in storage rings: The Use in storage rings: The ultimate ZAPS? ultimate ZAPS?

• Ultimate resolution: δp/p < 10-4

• Lab e- energy: 3-500 keV

Envisioned two-stage magnetic spectrometer(original ESR proposal Rido Mann et al 1988 – GSI)

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

μ – metal shielding/Helmholtz coils?

Resolution contributionsResolution contributions

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

Γ΄=100eV, ε΄=80keV, Δθ=0.20 (full-acceptance)Projectile Δp/p = 5 x 10-5, Spectrometer Δp/p = 1 x 10-4

ConclusionsConclusions

Important technical issues to take into consideration/resolveImportant technical issues to take into consideration/resolve::• IronIron or or Air -coreAir -core magnet design? magnet design? - Air-core seems better but needs more space!- Air-core seems better but needs more space! - Iron -core: problem of - Iron -core: problem of magnetic field uniformitymagnetic field uniformity over 1 m radius? over 1 m radius? problem of problem of Remanent magnetizationRemanent magnetization? ? • Solid angle considerations - small Solid angle considerations - small ΔθΔθ~0.1~0.100 (to limit (to limit kinematic broadening kinematic broadening for for

line width measurementsline width measurements)) will severely limit count rate – PSD necessary will severely limit count rate – PSD necessary• Good design, optical alignment and slit/baffle controls will be critical Good design, optical alignment and slit/baffle controls will be critical • High quality High quality non-magneticnon-magnetic materials to be used in the entire target area materials to be used in the entire target area• Need for highest areal density target (liquid HNeed for highest areal density target (liquid H22/He)/He)??• At the 10At the 10-5-5 precision level precision level - - Earth magnetic fieldEarth magnetic field annulment annulment ((μμ-metal shielding/large Helmholtz coils?)-metal shielding/large Helmholtz coils?)

- - Temperature Temperature stability to ~0.1stability to ~0.100 C C

Anybody up to the challenge? Come join the SPARC electron spectroscopy group!

http://www.gsi.de/fair/experiments/sparc/electron-spectrometers_e.html

BibliographyBibliography

• 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:For more information also check my home page:http://www.physics.uoc.gr/~tzouroshttp://www.physics.uoc.gr/~tzouros

XX International Symposium XX International Symposium on Ion-Atom collisions* andon Ion-Atom collisions* and

SPARC topical meeting on SPARC topical meeting on Electron spectrometry in the NESRElectron spectrometry in the NESR

August 1-4, 2007August 1-4, 2007Agios Nikolaos, Crete, GREECEAgios Nikolaos, Crete, GREECE

*a satellite of XXV ICPEAC - Freiburg

Resolution contributionsResolution contributions

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

Γ΄=10eV, ε΄=50keV, Δθ=0.20 (full-acceptance)Projectile Δp/p = 5 x 10-5 , Spectrometer Δp/p = 1 x 10-4

Resolution contributionsResolution contributions

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

Γ΄=10eV, ε΄=1keV, Δθ=0.20 (full-acceptance)Projectile Δp/p = 5 x 10-5 , Spectrometer Δp/p = 1 x 10-4

Kinematics: energy shifting and doubling IIKinematics: energy shifting and doubling II

44 6 8 10 20 40 60 80100 200 400 600

0.1

0.2

0.40.60.8

1

2

468

10

20

406080

100

200

400600800

1000

0.1

0.2

0.40.60.81

2

46810

20

406080100

200

4006008001000

Vp=v'V

p=v'

Projectile Rest frame e- energies ' 00: 1 keV 10 keV 50 keV 131.8 keV

1800: 1 keV 10 keV 50 keV 131.8 keV

± - 00 la

bora

tory

ele

ctro

n en

ergi

es (ke

V)

Projectile energy [MeV/u] (NESR range)

U91+ I.P. 131.8keV

Vp=v'

For He-like UraniumK-Auger series energies(75 -130 keV rest) frameRange in Lab from about100 - 1000 keV (+)40 - 0 keV (-)For projectile energies4 -740 MeV/u

Angular compression Angular compression – “beaming”– “beaming”

]''

sin[θ

:θ anglen observatio lab maximum a

is there1)/β'(β 1v'/VFor

max

max

pp

pp

Arc

100 200 300 400 500 600 700

20

40

60

80θmax

MeV/u

ε΄=131800eVε΄=75000eV

ε΄=10000eVε΄=1000eV

θmax

βp

β΄βAt 740 MeV/u we have:

For ε΄=1000 eV, θmax = 2.4070

ε΄= 10 eV, θmax = 0.240

Strong beaming for small electron energiesPractically total cross section measured around 00

All differential information averaged out

Kinematics: Kinematics: Line stretching and enhancingLine stretching and enhancing

)stretching mild - tic(relativis Γ|1β'β|γΓ

)stretching no - (classical |Γ|Γ

)β'βfor only (-

:gCompressinor Stretching Line Kinematic 0

'p'ppp

'p'p

p

0

tic)(relativis dΩ'dε'

σ'd

β'

)β'(βγ

dΩ'dε'

σ'd

p'

p

dεdΩ

σd

)yes! - (classical dΩ'dε'

σ'd

v'

v'V

dεdΩ

σd

tEnhancemen Line KinematicEnergy

tic)(relativis dΩ'dp'

σ'd)β'β(1γ

dΩ'dp'

σ'd

γ'

γ

dpdΩ

σd

)No! - (classical dΩ'dp'

σ'd

dpdΩ

σd

tEnhancemen Line Kinematic Momentum

2p

p

2

0θ

2

2p

0θ

2

2

pp

2

0θ

2

2

0θ

2

0

0

0

0

Natural Line widths Γ’ (rest frame) areChanged to widths Γ± in Lab frame

Mild enhancement and stretching in momentum analysis!!

PE=7 eVRanal=3%

Kinematic Widths and Enhancement factorsKinematic Widths and Enhancement factors

0 100 200 300 400 500 600 70090

200

300

400

500600700800900

2000

3000

p - momentum - energy

1 keV 75 keV 131.8 keV

Lab

wid

ths p

mom

entu

m (eV

/c) an

d

ener

gy (eV

)

Projectile energy (MeV/u)

'=100 eV

For atomsK line-widths dominated by Radiative widths at high ZAnd Auger widths at low ZWhat about Highly Charged Ions?

Momentum widths are stretched only weakly

While energy widths a lot!

Krause 1968

K-level natural

line widths

Zero-degree Auger Projectile electron spectra Zero-degree Auger Projectile electron spectra

Elastic scattering Elastic scattering on Bon B4+4+ and B and B3+3+

R-matrixR-matrix

ESMESM

R-matrixR-matrix

ESMESM