Transcript Slides - Agenda INFN

L. Serafini and C. Vicario - Introduction on Thomson Source
SPARCLAB: PW-class Ti:Sa laser+SPARC
Developed by
Amplitude Tech.
July 31st, 2008 - SPARC Review Meeting
FLAME laser layout and specs
July 31st, 2008 - SPARC Review Meeting
Parameter
specs
Energy
6J
Pulse length
> 20 fs
Peak power
300TW
Prepulsecontrast
10-8
ASE contrast
10-10
Rep rate
10 Hz
Laser FLAME transport to
compressor
to experimental
hall
Laser only
esperim
chamber
In vacuum
compressor
Laser
room
Diagnostics:
•Pulse length
•Contrast
•Energy
compressor
Main
beam
July 31st, 2008 - SPARC Review Meeting
Experimental set-up for the generation of tunable Xray radiation via Thomson scattering of optical
photons by relativistic electron bunches
10-20 m electron and
laser beam spot size
1 nC
0.1 to a few J laser pulses
tens of fs to ps long
July 31st, 2008 - SPARC Review Meeting
20-500 keV photons
106 to 109 per pulse
Inverse Compton Scattering
e-
energy = Ee= g me
q
lL
lX
 Normal Compton Scattering the photon has higher energy than the electron
 The inverse process has the Thomson cross-section when hx << Ee
 The scattered photon satisfies the undulator equation with period lL/2 for
1
q)
head-on collisions

(1+
g
single e
 103
lX = lL
NL
4g 
 Therefore, the x-ray energy decreases by a factor of 2 at an angle 1/2 g

e beam 2  0.05
n

July 31st, 2008 - SPARC Review Meeting

THOMSON BACK-SCATTERING
1  cos L
4g
2
T   0
 0
 4g  0
2 2
1  cosq
1 q g
for  L   and
q 1 or q  0
2
e- (1 GeV); l0=1µm, E0=1.24 eV
lT=6 x10-8µm, ET=20 MeV
e- (200 MeV); l0=1µm, E0=1.24 eV
lT=1.56 x10-6µm, ET=800 KeV
e- (29 MeV); l0=0.8µm, E0=1.5 eV
lT=0.5 x10-4µm, ET=20 KeV
July 31st, 2008 - SPARC Review Meeting
22%FWHM
5% FWHM
July 31st, 2008 - SPARC Review Meeting
QuickTime™ and a
TIFF (U ncompressed) decompressor
are needed to see this picture.
July 31st, 2008 - SPARC Review Meeting
Laser parameters delivered to
Thomson experiment
• Pulse energy 6 J
• Spot top hat, diameter 9 cm and
aperture 13.5 cm
• M2 = 1.5
• Pulse length 6 ps
• Max bandwidth 80 nm, central
wavelength range 800 nm
July 31st, 2008 - SPARC Review Meeting
Transport system: considerations
• Long transport (< 30 m) from the compressor to the
interaction chamber.
• To maximize the beam stability an achromatic relay
optical system and ultrastable mounts are foreseen.
• To avoid absorption and distortion effects pipeline
will be kept in low vacuum (10-3 mbar) upgradeable
at 10-6 mbar for future full compressed beam
transport.
• Delay line for temporal overlap between laser pulse
and electron beam.
• High energy large aperture optics: mirrors, filters,
beam samplers, achromats lenses.
July 31st, 2008 - SPARC Review Meeting
Layout SPARC hall
Optical transfer line
0.3 PW LASER
PHOTOINJ
LASER
SEEDING
LASER
PLASMON.X
THOMSON
HHG
DGL
PHOTOINJECTOR
UNDULATOR
July 31st, 2008 - SPARC Review Meeting
Laser transport overview
July 31st, 2008 - SPARC Review Meeting
Focusing system
• OffAxis Parabola (OAP)
– Achromatic focal system
– Reduced spherical aberrations
– Close to diffraction limited focal dimension
– Critical surface quality for maximum efficiency
– Large area to avoid optical-induced damage
(0.1 J/cm2 typical)
• Aperture 14 mm for Xray extraction
• Custom optics fabrication
July 31st, 2008 - SPARC Review Meeting
Simulated waist/2 vs focal and
wavelength
Flat mirror
Extraction
Interaction
July 31st, 2008 - SPARC Review Meeting
Vacuum port
Simulations with Zemax
optical design code
Off axis parabola
Optical layout and simulation
plane
mirror
plane
mirror
Vacuum
port
hole
OAP
Spot size at the interaction point
July 31st, 2008 - SPARC Review Meeting
Specs custom off-axis parabola
(OAP)
Focal length
diameter (clear aperture )
outer diameter
off axis distance (to vertex edge)
thickness
coating
substrate
surface accuracy
Scratch Dig:
geometric requirement
wavelength of test
back side
750 mm +/- 1 mm
<150 mm
<155 mm
>125 mm (preferable >150 mm)
not specified (25 mm?)
gold
Zerodur
Lambda/10 PTV 95% CA
60/40
hole at the center with 14 mm,
633 nm
plano
Few producers available; estimated cost 30-40 K€
July 31st, 2008 - SPARC Review Meeting
Tolerances on OAP position
Focal spot for 1 mrad OAP tilt!
• Distance to the interaction point
ΔL< 140 um (2 Reyleigh length)
• Tilt angles position <0.1 mrad
• Transverse displacement is
converted to direct translation
of the focus ΔD< 50 um
• A proper mount with 5 axis
control is required
July 31st, 2008 - SPARC Review Meeting
40um
100um
horizontal
tilt
vertical
tilt
Fundamental relations in the linear regime
• Relativistic upshift
4g 2
˜ 2   2   2  2 cos(   )
EX  E0
,

e
e
e
2 ˜2
(1 g  )
Particle incidence angles
• For an e-bunch the en. spread of the collected photons depends on
– Collecting angle qM
– Bunch energy spread
– Transverse emittance
  g M

 2

E X
g
n
2
2
 (g M )    +front
EX
g
 r  curvature
cT  2 2 (1 2  23 4 )
N()  N e  a0 
2 3
 l 
1  )
Overlap
July 31st, 2008 - SPARC Review Meeting
Minimum TS energy spread
• The minimum energy spread is
E X 
g  
  

  2
g  r 
 E X min

n
• With an energy spread 0.1%, emittance 1.5 mm mrad and beam
focusing size of 13 mm rms, the contributions are
2
g
g

3
 2  10
,
  0.1
 
2

  2  10
 r 

n
2
Minimum energy spread of 2% FWHM ,
with a flux of 1.3.109 photons/s

July 31st, 2008 - SPARC Review Meeting
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