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)

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 101 085002 (2008) (mono-energetic fraction: 10 pC@200 MeV, divergence=2.1 mrad FWHM) Koyama, Hosokai 20 pC @ 100 MeV and density downramp N. Hafz, Jongmin Lee , Nature photonics THCAU05 FEL Conf 2008

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,

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

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

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. 196 448 (2004) New results by ALADYN in the poster section Genesis 1.3 EURA Astra Retar Second stage

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) 7 10 18 Duration (fs) n01 (cm-3) 1 1019 LR(mm) 10 n02 (cm-3) 0.6 1019 lp (mm) 13

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

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

FEL interaction with a e.m. undulator = 1.35nm Pierce Parameter IA=17 103 Amp Ideal 1d model Erad=rEbeam Lg1d=lu/( 4pr) Three-dimensional model Lg=lu (1+h) /(31/24pr)

<1 , <1 <1

Requirements for the growth Generalized Pellegrini criterion

1.3 1.15 106 m-1 20 kA 50 5 X 10-6 m r=3 10-3

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

Transverse coherence d= Lsat*l/sx= 10*Lg*l/sx = 10*200 10-6*10-9/5 10-6=0.4 mm Longitudinal coherence Lc=l/(4pr ) (1+h) =0.04 mm 1 spike each 10 Lc

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

Laser requirements: 250 GW for 5 mm R=30 mm E=4.16J First peak Saturation Pmax (W) 2 10 8 1.5 108 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

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