1. ULTRA-HIGH BRIGHTNESS ELECTRON BEAMS BY PLASMA BASED INJECTORS FOR ALL
OPTICAL FREE-ELECTRON LASERS (AOFEL)
V. Petrillo, Università degli Studi, Milano (Italy) L.Serafini, P. Tomassini, INFN, Milano (Italy) C. Benedetti ,P. Londrillo, A. Sgattoni, G. Turchetti Università e INFN Bologna (Italy)

2. The technology of ultra short, high power lasers has permitted the production and the study of high-brightness, stable, low divergence, quasi mono-energetic electron beams by LWFA.
These beams are now an experimental reality (for instance: Faure et al.,Leemans et al., Jaroszinski et. al, Geddes et al., ecc.)
and can be used in applications for driving Free-electron lasers Last experimental results, see, for instance:
J.Osterhoff et al. PRL (2008)
(mono-energetic fraction: 10 MeV, divergence=2.1 mrad FWHM)
Koyama, Hosokai MeV and density downramp
N. Hafz, Jongmin Lee , Nature photonics
THCAU05 FEL Conf 2008

3. This last group tries to realize the scheme proposed by Gruener et al
This last group tries to realize the scheme proposed by Gruener et al. (1.74 GeV, 160 kA, 1mm mrad, DE/E=0.1%, sx=30 mm)
where an electron beam generated by LWFA in the bubble regime is driven in a static undulator
lu=5 mm, l=0.25nm, Lsat=5m, Lrad=4fs,Psat=58 GW,

4. AOFEL injection by longitudinal nonlinear breaking of the wave
at a density downramp looks one of the most promising
since it can produce e-beams having both low energy
spread and low transverse emittance.
electromagnetic undulator constituted by a laser pulse
conter propagating respect to the electron beam

5. AOFEL Lg=10.1 x (g sx2/3/I1/3)x(lw/K0/JJ2)1/3 CO2 envelope
Ti:Sa envelope
Ti:Sa pulse
electron beam
Gas jet
Lsat≈10 Lg
AOFEL

6. Scheme of the calculation
Third stage
First stage
Formation of the plasma
Formation of the bunch
Acceleration stage
Transition
Plasma-undulator
Beam-CO2 laser
Interaction
FEL instability
VORPAL
C. Nieter J. R. Cary
J.Comp.Phys
(2004)
New results by ALADYN in the poster section
Genesis 1.3
EURA
Astra Retar
Second stage

7. First stage:LWFA with a gas jet modulated in areas of different densities with sharp density gradients.
Energy (J) 2
Waist (mm) 20
Intensity (W/cm2)
Duration (fs)
n01 (cm-3)
1 1019
LR(mm) 10
n02 (cm-3)
lp (mm) 13

9. FEL : electron selector
<g>=55
<E>=27 MeV
I≈20 kA
ex<0.5 mm mrad
DE/E≈2 10-3,10-2
Q=55 pC
Best slices

10. Second stage: Transition from the plasma to the interaction area with the e.m. undulator (analysis by ASTRA)
With space charge
Without space charge

11. FEL interaction with a e.m. undulator
= 1.35nm
Pierce Parameter
IA= Amp
Ideal 1d model
Erad=rEbeam
Lg1d=lu/(
4pr)
Three-dimensional model
Lg=lu (1+h) /(31/24pr)

12. <1 ,
<1
<1

13. Requirements for the growth
Generalized
Pellegrini criterion

14. 1.3
m-1
20 kA 50
5 X 10-6 m
r=3 10-3

15. Lg1d=76 mm
sz=0.2 mm
Lg=200 mm

16. Transverse coherence
d= Lsat*l/sx= 10*Lg*l/sx
= 10* *10-9/5 10-6=0.4 mm
Longitudinal coherence
Lc=l/(4pr ) (1+h) =0.04 mm
1 spike each 10 Lc

17. Third stage: FEL radiation l=lu(1+aw2)/4g2 by uploading the particles by VORPAL
Superradiant
structure
Monochromatic
pulse
Single spike structure
0.1 mm=330 as

18. Laser requirements: 250 GW for 5 mm R=30 mm E=4.16J First peak
Saturation
Pmax (W)
2 10 8
E (mJ)
0.05
0.12
LR(mm)
0.5
Lsat (mm) 1.
4.5
lR(nm)
1.35
dlR/lR
0.81%
25 micron
25 micron
Laser requirements:
250 GW for 5 mm
R=30 mm E=4.16J

19. Conclusions
All optical free-electron laser are possible with e-beam produced by LWFA in density downramp + electromagnetic undulators
Characteristics of radiation: small energy, small transverse coherence, very short pulse, longitudinal coherence, monochromaticity
Injection of the beam, control of the exit from the plasma, requirements of power and structure of the e. m. undulator