Laser Electron Scatter Photons at Light Sources For Nuclear & Allied Research
UOS and CLS, April 21-23, 2010
Gamma Ray Production at
Synchrotron Light Sources
Schin Daté
Accelerator Division, SPring-8/JASRI
Contents
I. Intense 10 MeV γ Production in Light Sources
II. Some LEPS Experiences and LEPS-II
I. Intense 10 MeV γ Production in Light Sources
1. Well known facts about Compton back scattering
Eγ
θ
Ee
(1)
Energy
dσ
dE γ
(2)
Angle
θ = θ (E γ ) ,
(3)
Controlled Polarization
(4)
Yield
~ flat ,
εL
εL ≤ E γ ≤ E γ max ≈ 4 γ e 2εL
< θ 2 >≈ 1/ γ e
2
N?γ = 2.1×10 7 (s−1 )σ [b]I[A]λL [μm]l[m]PL [W ]/ sL [mm 2 ]
−1
= 1.34 ×10 (s )PL [W ]
8
for
σ = 0.5 b
I = 100 mA
λL = 10 μm
l = 10 m
sL = π (0.5 mm) 2
Progress in laser technology
Single mode CW output power (W)
Fiber Laser
Yb fiber laser (IPG): 1030 ~ 1050 μm
φ15μm core
year
CW single mode 2 kW
multimode 20 kW
bundled fiber line of, say, cmφ is possible to make
Heat load limit ~ 20 MW / mmφ
Polarization?
100 kW output is cleared in this way
Egmax
2. Production of Intense 10 MeV γ Rays
(1) Enegy aperture
Spring-8
CLS
DFELL
8
2.9
0.24-1.2
h
2436
285
64
96
1320
α
1.68 ×10−4
3.8 ×10−3
8.6 ×10−3
7.45 ×10−4
3.7 ×10−4
16
0.876
42 keV
0.712
0.816
q
4/3
2.74
17.1
1.7
4.04
δE max [MeV]
154
45
91
91
E 0 [GeV]
U 0 [MeV]
19 @ 500 MeV
30 @ 1.2 GeV
MAX-IV
3
NSLS-II
3
(2) Longitudinal beam quality
N?γ = 1011 s−1
⇒ Pγ / e− pass = 10−7
I = 100 mA
Spring-8
CLS
DFELL
MAX-IV
NSLS-II
T0 (μs)
4.8
0.57
0.36
0.96
2.6
α s−1 (ms)
4.2
1.9
4.3
4
9.7
−1
10 7 T0 >> α s
No serious effect on the longitudinal beam quality
Why Do We Want 10^11 /s Photons?
Because many interesting elementary interactions occur with σ ~ pb
ρ = 10 g / cm^3
σ = 1 pb
⇒
l = 1 cm
⇒
ρ N l = 6 b−1
N?γ σρl = 0.6 s−1 for N?γ = 1011 s−1
Old proposal
SPring
8
Summary of Part I
There is no crucial problem to producee very intense (~ 10^11 /s)
10 MeV gamma rays in 3 GeV light sources including CLS, MAX IV and NSLS-II..
There are technologies available to realize the intense gamma production.
Now is the adequate time to consider such a possibility seriously.
II. Some LEPS Experiences and LEPS-II
Optical param bl33
x’ (rad)
star
x (m)
SPring
8
New Beamline Project at SPring-8
High intensity：
Multi (ex. 4) laser injection w/
Backward Compton Scattering
large aperture beam-line &
8 GeV electron
Laser beam shaping
~10 7 photons/s （LEPS ~10 6 ）
Recoil electron
30m
(Tagging) High energy：Re-injection of
（LE lo
X-ray from undulator
PS ng l
7.8 ine
m)
Eγ < 7.5GeV (LEPS < 3GeV)
Laser or
re-injected
X-ray
SPring-8 SR ring
GeV γ-ray
Inside
Better divergence beam
Outside
building
⇒collimated photon beam
building
Different focus points for
Laser hutch
multi CW laser injection
Large 4π spectrometer based on
BNL-E949 detector system.
Better resolutions are expected.
New DAQ system will be adopted.
Experimental hutch
optical parameters
γ beam divergence
33LEP LSS
<σ x’ > [μrad] 58
23
1.2
0.30
12
<σ y’ > [μrad] 1.8
<σ x > [mm]
<σ y > [μm]
<=
( εx =
0.34
12
<=> <σ x’ >BCS ~ 64 μrad
γ beam divergence in LSS
BL is dominated by Compton
scattering.
Contributions are wighted for Gaussian laser beam.
Values are valid for the laser waist radius > 0.5 mm.
3.4 ×10-9 m⋅ rad
,
εy
εx = 0.2 %
)
Tracking of recoil electrons
Incident electrons
dσ Klein−Nishina
dt
γ
Incident Laser beam
tagger
Result for LEP with 350nm laser
33B2
31B1
We expect better energy resolutions
In the new LEPSII BL.
High Energy Backward Compton
Photons
HELP production by X-ray re-injection