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LPAW07. Tomassini, INFN sez. di Milano 1 Linear and nonlinear TS for advanced X/  sources in PLASMONX P.Tomassini(1,2), A. Bacci(1), S.Betti (3), J. Cary.

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Presentation on theme: "LPAW07. Tomassini, INFN sez. di Milano 1 Linear and nonlinear TS for advanced X/  sources in PLASMONX P.Tomassini(1,2), A. Bacci(1), S.Betti (3), J. Cary."— Presentation transcript:

1 LPAW07. Tomassini, INFN sez. di Milano 1 Linear and nonlinear TS for advanced X/  sources in PLASMONX P.Tomassini(1,2), A. Bacci(1), S.Betti (3), J. Cary (6), A.Giulietti(2), D. Giulietti(2,3,5), L.A. Gizzi (2), L. Labate(2), L. Serafini(1), V. Petrillo(1) (1) INFN Sect. of Milano (2) IPCF-CNR, Pisa (3) Dip. Fisica Univ. di Pisa (4) Dip. Fisica Univ. di Milano (5) INFN Sect. of Pisa (6) U. of Colorado and Tech-X corp. University of Milan

2 LPAW07. Tomassini, INFN sez. di Milano 2 Thomson Scattering Activities in PLASMONX (coordinator: V. Petrillo, INFN&Univ. MI) We ave optimized the TS source aiming at producing HIGH FLUX quasi-monochromatic X/  radiation (energy in the range 10KeV-600KeV for PLASMONX) for medical imaging (e.g. mammography) with a high-charge (1-2.5 nC e-beam). Ultrashort quasi-monochromatic X beams with a low-charge (20pC) ultrashort (30-50fs) photoinjector e-beam : We are currently studying: All-optical HIGH FLUX-Ultrashort tunable X/  sources with LWFA produced e-beams Coherent generation of X photons via optical FEL Finally, we plan to use TS as a diagnostics on the LWFA produced e- beam

3 LPAW07. Tomassini, INFN sez. di Milano 3 Outline Uncoherent Thomson Scattering in the linear and nonlinear regimes High-flux source in the quasi-linear regime Ultra-short quasi-monochromatic fs source with RF- photoinjector High-flux Ultra-short fs source with LWFA e-beams

4 LPAW07. Tomassini, INFN sez. di Milano 4 1. Particles do experience : 1.a Longitudinal ponderomotive forces at the rising and falling edges of the laser pulse -> lowering of the longitudinal momentum inside the pulse 1.b Transverse ponderomotive forces 1.c Transverse force due to the pulse electric field in the case of short rising edge 2. Particles motion is: 2.a Secolar motion is longitudinal, with a transverse drift. Longitudinal and transverse quivering Note: In a strong transverse quivering regime several harmonics can be generated (Nonlinear Thomson regime or multiphoton absorbtion regime) Thomson Backscattering: relevant issues -> off axis momentum

5 LPAW07. Tomassini, INFN sez. di Milano 5 Scattered photons distributions The computation of the angular and spectral distribution of the scattered radiation can be performed in the classical dynamics framework by using the retarded potentials : Main features of the scattered radiation Main features of the scattered radiation : 1.It is emitted forward with respect to the direction of the mean speed, within a cone of aperture  c  2.It is blue shifted of a factor depending on the emission angle , the electron energy and the pulse amplitude: 3.As the normalized amplitude a 0 exceeds unity, a large number of harmonics is produced. Full treatement of linear and nonlinear TS for a plane-wave laser pulse with analytical expression of the distributions as well as several approximate expressions in P. Tomassini et al., Appl. Phys. B 80, 419 (2005).

6 LPAW07. Tomassini, INFN sez. di Milano 6 Quasi head-on collision of a 5 MeV electron (  e = 50 mrad,  e =  /2) on a flat-top pulse of normalized ampliude a0=1.5, = 1  m and T = 20 fs Example P. Tomassini et al., Appl. Phys. B 80, 419 (2005)

7 LPAW07. Tomassini, INFN sez. di Milano 7 Fundamental relations in the linear regime Relativistic upshift For an e-bunch the energy spread of the collected photons depends on –Collecting angle  M –Bunch energy spread –Transverse emittance Particle incidence angles Overlap +front curvature

8 LPAW07. Tomassini, INFN sez. di Milano 8 Trivial : Charge: as large as possible; Size: as low as possible; Monocromaticity: as large as possibile Less trivial : Usually the beam normalized emittance is quoted to quantify the goodness of an e-beam. For TS the minimum energy spread is determined by the normalized acceptance angle which should exceeds the normalized mean incident angle of the particles transverse relevant parameter. The relevant parameter is then the rms of the transverse momentum of the bunch Bunch Requirements

9 LPAW07. Tomassini, INFN sez. di Milano 9 Uncoherent TS Simulation tools in PLASMONX Nonlinear dynamics in the single-particle approximation: TS (TS) 2 (Thomson Scattering Simulation Tools) [P.Tomassini, 2004]. Semi-analytical FAST tools that employes the analytical results of P. Tomassini et al., Appl. Phys. B 80, 419 (2005) with a generalization to Gaussian pulses. The code accounts for (i) nonlinear effects, (ii) pulse focusing, (iii) full effects of beam emittances Linear dynamics in the single particle approximatin [V. Petrillo et al., 2004].

10 LPAW07. Tomassini, INFN sez. di Milano 10 Outline Uncoherent Thomson Scattering in the linear and nonlinear regimes High-flux source in the quasi-linear regime Ultra-short quasi- monochromatic fs source with RF- photoinjector High-flux Ultra-short fs source with LWFA e-beams

11 LPAW07. Tomassini, INFN sez. di Milano 11 High Flux operation mode A long (ps scale) laser pulse is employed (weakly nonlinear regime) to reduce harmonics and energy spread High charge (1-2.5nC) e-beam. Due to the large charge, it is difficult to obtain small beams (length of ps scale) Mammography Monochromatic Beam Outlook (Current optimization for mammography sources in collaboration with the Mammography Monochromatic Beam Outlook (MAMBO) I.N.F.N. experiment requiring >10 10  /s with energy spread <12% rms. Best working point Pulse 2.5nC 8ps long (full size) 13  m rms tr. Size 1.5 mm mrad norm emittance 0.1% energy spread Bunch TEM00 6J in 6ps w 0 = 15  m

12 LINAC layout Features: High brightnss e-beam Very low emittance

13 LPAW07. Tomassini, INFN sez. di Milano 13 High Flux results Optimization of the bunch in progress. Front-to-end simulations from photo-gun to the final focus. Optimization of the pulse parameters: scan of the distribution with the waist size and duration. Acceptance:  max = 0.5 Reduced overlapping

14 LPAW07. Tomassini, INFN sez. di Milano 14 (E,  ) Distribution Second harmonics Third harmonics

15 LPAW07. Tomassini, INFN sez. di Milano 15 22%FWHM 5% FWHM

16 LPAW07. Tomassini, INFN sez. di Milano 16 Minimum TS energy spread The minimum energy spread is With an energy spread 0.1%, emittance 1.5 mm mrad and beam focusing size of 13 mm rms, the contributions are Minimum energy spread of 2% FWHM, with a flux of photons/s

17 LPAW07. Tomassini, INFN sez. di Milano 17 Outline Uncoherent Thomson Scattering in the linear and nonlinear regimes High-flux source in the quasi-linear regime Ultra-short quasi-monochromatic fs source with RF-photoinjector High-flux Ultra-short fs source with LWFA e- beams

18 LPAW07. Tomassini, INFN sez. di Milano 18 Ultrashort Quasi-monochromatic Source with Photoinjector e-Beam Ultrashort 130MeV, 20pC e-beam Parameters: r (rms)=6  m length (rms)=13  m  E/E=0.1%  n =1.2mm mrad

19 LPAW07. Tomassini, INFN sez. di Milano 19 TS Distributions Since the emphasis is on the monochromaticity we choose to collect photons in the “natural-aperture” cone, i.e. the one with  e =0.2 (approx. 1 mrad). Monochromaticicy requires minimization of the harmonics production. The laser pulse is 5ps long and is focused down to 15  m of waist size Fundamental at 400KeV First harmonics at 800 KeV Bunch 45fs long (rms) with 2x10 8 photons/sec  E/E=4% FWHM energy spread

20 LPAW07. Tomassini, INFN sez. di Milano 20 Outline Uncoherent Thomson Scattering in the linear and nonlinear regimes High-flux source in the quasi-linear regime Ultra-short fs source with RF-photoinjector High-flux Ultra-short fs source with LWFA e- beams

21 LPAW07. Tomassini, INFN sez. di Milano 21 All-optical source: LWFA self-inj. e-beam We are currently exploring controlled self injection with density downramp S. Bulanov et al. [the idea+1D sim.] PRE 58 R5257 (1998) P. Tomassini et al. [ 2D sim+optimization for monocromaticity and low emittance ] PRST-AB (2003). T. Hosokai et al., [ First experimental paper of LWFA with injection by density decrease ] PRE 67, (2003). Search for working points in the MeV energy range, with –ultrashort, –low transverse momentum –quasi monochromatic e-beams For monocromaticity of The X source Few femtoseconds

22 LPAW07. Tomassini, INFN sez. di Milano 22 2D PIC preliminary results with the VORPAL code Macro-particles move in a moving-window simulation box of 30x40  m 2 with a spatial resolution of 0.05  and  0.15  and 20ppc The plasma density is large ( cm -3 ) in order to “freeze” the space-charge effects and slippage in the early stage of acceleration. The density transition was (L~5  m ~ p ). The amplitude of the transition is low (20%), thus producing a SHORT e-beam The laser pulse intensity (I= W/cm 2 ) 0.8J in 20fs focused on a waist of 12  m) was tuned in order to produce a wakefield far from wavebreaking in the flat regions. The pulse waist was chosen in order to assure that longitudinal effects do dominate over transverse (avoid transverse wavebreaking)

23 LPAW07. Tomassini, INFN sez. di Milano 23 Main bunch parameters: Charge: 5-20pC Length 0.27  m (rms) Transverse size 0.47  m (rms) Transverse momentum 0.58 mc (rms) Normalized emittance 0.23 mm mrad Energy 31MeV Energy spread 10% (rms)

24 LPAW07. Tomassini, INFN sez. di Milano 24 Since the emphasis is on the monochromaticity we choose to collect photons in the “natural-aperture” cone, i.e. the one with  e =0.5 (approx. 8 mrad). As for the case of the Photoinjector e-beam, monochromaticicy requires minimization of the harmonics production. The laser pulse is 5ps long and is focused down to 15  m of waist size Fundamental at 25KeV First harmonics at 50 KeV TS Distributions Bunch 1fs long (rms) with 4x10 8 photons/sec  E/E=15% FWHM energy spread

25 LPAW07. Tomassini, INFN sez. di Milano 25 In the full Nonlinear regime? wo=10  m, T=40fs ->ao=7 a huge amount of harmonics, including downshots is observed

26 LPAW07. Tomassini, INFN sez. di Milano 26 Conclusions The Thomson Scattering beamline in PLASMONX can be tuned to produce high flux quasi-monochromatic X rays. With the optimization of the parameters for mammography a flux of 2. 10^10 20KeV with 22%FWHM enegy spread is obtained. Higher monochromaticity is obtainable with a lower acceptance angle (with a proportional reduction of the flux) down to the minimum energy spread of 2% with 10 9 photons/s. The beamline can be tuned to produce ultrashort TS with the PLASMONX parameters can produce 45fs long (rms) X/  rays with 2x10 8 photons/sec with  E/E=4% FWHM of energy spread An all-optical TS source is being investigated. (Very) preliminary simulations show that the density downramp self-injection scheme is capable of producing extremely ultrashort (0.3  m->1fs) e-beams thus allowing the production of a femtosecond-scale tunable quasi-monocromatic source of 4x108 photons/sec with  E/E=15% FWHM energy spread.


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