Transcript 740 MeV/u

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)
Emission from moving source
Kinematics: Laboratory energy Shifting and Doubling
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   1pβ 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]
2nd order fractional momentum broadening :
ΔB
V
p  Δθ 2 p

(classical )
p
8 v'

ΔB
p
p

β | 1  β β' |
Δθ 2 p
p

8 β' (1 - β 2 )
p
Range in spectrometer acceptance angle Δθ
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