Page 1
Overview of Compton Scattering Light Sources & Applications
F.V. Hartemann, F. Albert, S. G. Anderson, A.J. Bayramian, T.S. Chu, R.R. Cross, C.A. Ebbers, D. J. Gibson, T. L. Houck, A.S.
Ladran, R.A. Marsh, M. J. Messerly, V. A. Semenov, M.Y. Shverdin, S.S. Wu, R.D. Scarpetti, Jr., C.W. Siders, D.P.
McNabb, R.E. Bonanno, and C.P.J. Barty LLNL, Livermore, CA 94550, U.S.A.
C.E. Adolphsen, E.N. Jongewaard, Z. Li, S.G. Tantawi, A.E. Vlieks, J.W. Wang and T.O. Raubenheimer
SLAC National Accelerator Lab, Stanford, CA 94025, U.S.A.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Page 2
Overview • Compton scattering
– Introduction – The case for high energy – Physics & modeling
• Technology – RF gun & photocathode laser – Electron accelerator – Interaction laser
• Applications – NRF – Photo-fission
• Experiments
Page 3
Compton scattering (1923)
Page 5
Compton formula
• Energy-momentum conservation
uµ = γ 1,β( ) kµ = ωc
,k⎛⎝⎜
⎞⎠⎟
uµ + kµ = vµ + qµ =
m0c
qk= γ − ucosϕγ − ucosθ + k 1+ cos θ − ϕ( )⎡⎣ ⎤⎦
Page 6
Tuning and recoil
• 532 nm, head-on collisions, on-axis radiation
NRF
Δω /ω = 10−3
Page 7
Angular correlation
Page 8
Quick brightness estimate
• Phase space density (on-axis, head-on) – Total dose (100%bw) – 0.1% bandwidth – Pulse duration: e-beam – Source size & divergence: geometric emittance
– 0.1 nC, 0.01 photon/e-, 5 ps, 1 mm.mrad, 250 MeV – 3 x 1020 photons/(s x 0.1% bw x mm2 x mrad2)
Bx ≈ Ne ×QE ×10−3 × 1
Δτ× γ 2
εn2
Page 9
Brightness optimization
Page 10
The case for high energy
• Brightness scales as • Scattering cross-section is essentially energy-
independent • Quantum efficiency depends on interaction
geometry (beams overlap) • Photon energy roughly scales as • Source efficiency can be high (%), even
compared to SASE FEL • Example: 250 MeV electrons, 2.2 MeV photons
γ2 / εn
2
γ2
Page 11
Compton scattering light sources
• 1923 Compton scattering
• 1928 Linac – Widerøe, Rolf Archiv Elektronik und
Uebertragungstechnik 21: 387 (1928)
• 1939 Klystron
Page 12
Compton scattering light sources
• 1960 Laser
• 1965 First experiments using a laser
Page 13
Compton scattering light sources
• 1985 CPA
• 1989 RF Gun
• Emittance compensation (Bruce Carlsten)
Page 14
Laser/electron beam collisions
Page 15
Modeling
• 3 main approaches: – Differential scattering cross-section – Radiation integral (Thomson scattering) – Monte Carlo simulations
Page 16
Differential scattering cross-section
• Method: incoherently sum discrete e-/photon interactions over laser and electron beam phase spaces
• Pros: – Recoil properly accounted for – Spin & magnetic corrections can be included
• Cons: – Nonlinear interactions much harder to describe – Laser phase space correlations require Wigner function
formalism
Page 17
Radiation integral
• Method: Fourier transform e- trajectories
• Pros: – Readily accounts for diffraction, pulse chirp and other
incident laser phase space correlations – Easily extended to include nonlinear effects
• Cons: – Does not include recoil – Cross-section is valid for low-energy, no spin
d 2NdqdΩ
= α4π 2 q π µu
µe− iqνxν dτ−∞
+∞
∫2
Page 18
Thomson scattering
• Radiation formula
• Use phase as independent variable
d 2NdqdΩ
= α4π 2 q π µu
µe− iqνxν dτ−∞
+∞
∫2
d 2NdqdΩ
= α4π 2
qκ 2 π µ uµ φ( )e− iqν
uν
κdψ∫ dφ
−∞
+∞
∫2
Page 19
Thomson scattering
• Light cone variables (Feynman)
• Electron trajectory (ballistic + linear oscillation)
uµ = uµ
0 + Aµ − kµ
Aνu0ν
kνu0ν , xµ − xµ
0 =uµ
0
κφ
κ = uµ0k µ , λ = uµ
0qµ
κ − λ = kµqµ
Page 20
Thomson scattering
• 4-polarization
• Radiation spectrum
• Fourier transform of delta-function • Identical to Compton formula, but no recoil
d 2NdqdΩ
= α4π 2
qκ 2 A0
2 e− iqνx0ν 2
π µεµ 2
eiφ 1−λ
κ⎛⎝⎜
⎞⎠⎟ dφ
−∞
+∞
∫2
εµ = 1
−AνAνAµ − kµ
Aνu0ν
kνu0ν
⎛
⎝⎜
⎞
⎠⎟ , εµε
µ = −1
Page 21
Klein-Nishina cross-section
• Spin-independent component
dσdΩ
= α2
2qκ
⎛⎝⎜
⎞⎠⎟
2
12
κλ+ λκ
⎛⎝⎜
⎞⎠⎟−1
+2 εµπµ −
εµuµ( ) πµv
µ( )κ
+εµv
µ( ) πµuµ( )
λ
⎡
⎣⎢⎢
⎤
⎦⎥⎥
2
⎧
⎨
⎪⎪⎪
⎩
⎪⎪⎪
⎫
⎬
⎪⎪⎪
⎭
⎪⎪⎪
Page 22
Klein-Nishina cross-section
• For large values of recoil, the cross-section deviates from the Thomson scattering dipole
x y, z,( )
x y, z,( )
x y, z,( )
! =
=!
00
0, 0.5, 1.0C
k
Page 23
Compton/Thomson comparison
• Compton formula limit
• Energy-momentum limit
• Cross-section limit
κ − λ = kµqµ →κ = λ
uµ + kµ = vµ + qµ → uµ = vµ
dσdΩ
= α2
2qκ
⎛⎝⎜
⎞⎠⎟
2
12
κλ+ λκ
⎛⎝⎜
⎞⎠⎟−1
+2 εµπµ −
εµuµ( ) πµv
µ( )κ
+εµv
µ( ) πµuµ( )
λ
⎡
⎣⎢⎢
⎤
⎦⎥⎥
2
⎧
⎨
⎪⎪⎪
⎩
⎪⎪⎪
⎫
⎬
⎪⎪⎪
⎭
⎪⎪⎪
Page 24
Adding recoil to Thomson scattering
• Motivation – The cross-section differences between Thomson and
Compton scattering are a higher-order perturbation in ħ than the frequency shift due to recoil
– Recoil becomes significant (%) for MeV photons • Approach
– Add the appropriate correction term for plane waves in the linear regime
– Generalize
Page 25
Plane wave
• Modify electron trajectory
• Radiation integral contains recoil term
uµ = uµ0 + Aµ − kµ
Aνu0ν
kνu0ν + kµ
xµ − xµ0 =
uµ0 + kµ
κ
⎛
⎝⎜
⎞
⎠⎟ φ
d 2NdqdΩ
= α4π 2
qκ 2 A0
2 e− iqνx0ν 2
π µεµ 2
eiφ 1−
λ+qνkν
κ
⎛
⎝⎜
⎞
⎠⎟
dφ−∞
+∞
∫2
κ − λ = kµqµ
Page 26
Nonlinear radiation phase
• Plane wave
• Resonance (periodicity)
qµxµ = qµxµ0 + 1
κ
φ λ + kµqµn +
−AνAν
2κ
⎛
⎝⎜⎜
⎞
⎠⎟⎟
⎡
⎣
⎢⎢
⎤
⎦
⎥⎥+ cosφA0
uν0aν
κaµ − kµ
⎛
⎝⎜
⎞
⎠⎟ qµ
+sinφA0σuν
0bν
κbµ − kµ
⎛
⎝⎜
⎞
⎠⎟ qµ + sin2φ
kµqµ
2κσ2 −1
4
⎧
⎨
⎪⎪⎪
⎩
⎪⎪⎪
⎫
⎬
⎪⎪⎪
⎭
⎪⎪⎪
qnµ
κuµ
0 + nkµ +kµ
2κ−AνA
ν⎛
⎝⎜
⎞
⎠⎟ = n
Page 27
Compare with nonlinear Compton
• Energy-momentum conservation
• Incident wave is coherent
• Replace velocity by nonlinear solution
uµ + C kµ1 + kµ
2 +…kµn( ) = vµ + Cqµ
n
kµ1 = kµ
2 =… = kµn
uµ0 + Aµ − kµ
AνAν + 2uν
0Aν
2uν0k ν
⎛
⎝⎜
⎞
⎠⎟ nkµ − qn
µ( ) = nkµqnµ
nuµ0kµ − uµ
0 −kµ
2uν0k ν AνA
ν⎛
⎝⎜
⎞
⎠⎟ qn
µ = nkµqnµ
Page 28
Nonlinear Compton formula
• Nonlinear Compton scattering frequency – Nonlinear radiation pressure – Multi-photon recoil
• Nonlinear radiation pressure – Scales as A0
2Δφ
nκ − λ = kµqn
µ n +−AνA
ν
2κ
⎛
⎝⎜⎜
⎞
⎠⎟⎟
d 2NdqdΩ
= α4π 2
χk
A0eiχA0
2Δφ xsinφ + ycosφcosh φ / Δφ( ) exp iχ φ 1+ r( ) + A0
2Δφ tanh φΔφ
⎛⎝⎜
⎞⎠⎟
⎡
⎣⎢
⎤
⎦⎥
⎧⎨⎪
⎩⎪
⎫⎬⎪
⎭⎪dφ
−∞
+∞
∫2
Page 29
Nonlinear effects
• Low-intensity: inhomogeneous radiation pressure, dressed electron mass
• High-intensity: harmonic production, multi-photon effects
• Synchrotron-like radiation (projection of the linear oscillation component along the direction of observation)
Page 30
3D trajectories
!400 !200 0 200 400!0.010
!0.005
0.000
0.005
Φ
ux
!400 !200 0 200 400
0
1."10!9
2."10!9
3."10!9
4."10!9
5."10!9
6."10!9
Φ
! !$Φ"u z#%
Ψ
Page 31
3D nonlinear spectra
!60000 !40000 !20000 0 20000 40000 600000.00
0.05
0.10
0.15
0.20
0.25
Φ!20000 !10000 0 10000 20000
0.0
0.2
0.4
0.6
0.8
Φ
0.9990 0.9992 0.9994 0.9996 0.9998 1.0000 1.0002 1.0004
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Doppler!shifted Frequency, Χ0.996 0.997 0.998 0.999 1.000 1.001
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Normalized Doppler!shifted Frequency, Χ
Page 32
Interaction probability vs. spectral purity
• The interaction probability and the radiation pressure dephasing scale identically
• Rule of thumb: A0
2 ≈ Δφ ≈ 1k0
2w02
dNdτ
= σcuµk
µ
γ knλ rν τ( )⎡⎣ ⎤⎦ nλ ∝ A0
2
d 2NdqdΩ
= α4π 2
qκ 2 π µ uµ φ( )e− iΦ dφ
−∞
+∞
∫2
Φ = φκ
qµu0µ + qµk
µ( ) + qµkµ
2κ 2 A02 g2 ψ( ) sin2ψ +σ 2 cos2ψ( )dψ
−∞
φ
∫
Page 33
3D nonlinear spectra + electron beam phase space
0.9990 0.9995 1.0000 1.0005 1.00100
10000
20000
30000
40000
50000
60000
70000
Normalized Doppler!shifted Frequency, Χ0.997 0.998 0.999 1.000 1.001
0
10000
20000
30000
40000
50000
60000
Normalized Doppler!shifted Frequency, Χ
0.95 0.96 0.97 0.98 0.99 1.000
20000
40000
60000
80000
Normalized Doppler!shifted Frequency, Χ
0.95 0.96 0.97 0.98 0.99 1.000
5.0#106
1.0#107
1.5#107
2.0#107
2.5#107
3.0#107
Normalized Doppler!shifted Frequency, Χ
Page 34
Nonlinear effects
Page 35
Nonlinear effects
Page 36
Typical experimental setups
Electron source Thermionic Field emission Photo-emission Plasma
Accelerator Warm rf SC Electrostatic Laser wakefield
Radiator Laser FEL
Re-circulation Storage ring ERL Cavity RING
Page 37
Technology
• Example: 2 MeV source for NRF • RF gun • Photocathode laser • Electron accelerator • Interaction laser • 5-10 year challenges
Page 38
System Overview
• RF gun: 5.59 cells, 11.424 GHz, 200 MV/m • Photocathode laser: Fiber-based, 4th harmonic, 50 uJ • Linac: 250 MeV, 11.424 GHz, > 75 MV/m • Interaction laser: 0.5 J, 1.064 nm, 10 ps; 0.1 J, 2ω • Nominal rep. rate: 60-120 Hz • Dose: 107-108/shot • Flux: 1010/s • Energy range: 0.5 – 2.2 MeV • Spectral bandwidth: 0.5%
Page 39
5.59 Cell X-band RF gun • Cathode electric field: 200 MV/m • Bunch duration: 10o 2.5 ps • Injection phase: optimized for each geometry; 20o for 5.59-cells • Charge: 250 pC • Emittance: as low as 0.18 mm.mrad
Page 40
400 MW 11.424 GHz RF power • The requirements on rf phase and amplitude stability are very stringent • 1o rf phase (243 fs), 0.1% • ScandiNova solid-state modulators • SLAC XL-4 klystrons + SLED-II
Page 41
X-Band RF power distribution
Page 42
250 MeV X-band linac
Interac,onRegion
Chicane
X‐BandRFGun
T53LinacSec,ons
Page 43
Sub-picosecond timing
Page 44
1 J 120 Hz Diode-pumped amplifier The1‐J120‐HzInjec0onLaser(HIL)isarelay‐imagedmasteroscillatorpoweramplifierbasedoncommercialdiodepumpedamplifierheads
Page 45
ILS compressor & SHG
Page 46
Applications
• Ultrafast x-ray diffraction • Medical x-rays
– Ron Ruth, Lyncean – Frank Caroll et al., MXI
• Protein crystallography – Ron Ruth, Lyncean
• Pulsed positrons • NRF • Photo-fission
Page 47
NRF mission space
Page 48
T-REX key properties
T-REX is a 0.1 - 0.9 MeV source
106 photons/s
6 x 10 mrad2
~ 10% bandwidth
Page 49
Nuclear resonance fluorescence • Isotopic sensitivity • Large cross-sections • Narrow bandwidth (~10-6) • Bertozzi detection method
Page 50
Direct detection of 7LiH behind Pb
• LN2-cooled HPGe
Page 51
Indirect detection of 7LiH
• Observation of resonant attenuation of gamma-rays in the transmitted beam
• Low false positive/negative rate
Interrogated sample Movable
Reference “notch” detector
gamma‐rays
Bertozzi method
Shielding
LiH
LiH
Page 52
Target material present
LiH
LiH
- No NRF Detected - Resonant photons absorbed by interrogated sample
Page 53
Target material absent
• NRF detected
Page 68
Nonlinear Thomson scattering, Umstadter et al. (1998)