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Electron bunch length in laser-plasma acceleration.

Explore the mechanisms determining electron bunch length in laser-plasma acceleration experiments, crucial for future applications. Experimental findings and simulations contribute to understanding and control in multi-stage systems.

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Electron bunch length in laser-plasma acceleration.

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  1. Electron bunch length in laser-plasma acceleration. Danilo Giulietti1 and Alessandro Curcio2 1Physics Department of the University and INFN, Pisa, Italy also at ENEA, Centro Ricerche Frascati 2CERN, Geneva, Switzerland

  2. ABSTRACT Many experiments have been conducted in recent years in which electron bunches have been accelerated during the interaction of ultra-short and ultra-intense laser pulses with thin solid targets. Several causes can be taken into consideration which contribute to the determination of the measured bunch length at the exit of the targets. These include the temporal and velocity distributions of the electrons accelerated at the plasma critical surface and, eventually, the characteristics of the pre-plasma in which other acceleration processes can develop as well.The understanding of these mechanisms will allow, in the future, for controlling the duration of an electron bunch generated with these techniques, which is necessary for several applications as, for example, multi-stage laser-plasma acceleration systems.

  3. SUMMARY • THE LOA EXPERIMENT • E-BUNCH LENGTH AND ACCELERATION REGION • E-BUNCH LENGTH DUE TO THE ENERGY SPREAD AND PROPAGATION • CONCLUSIONS

  4. SUMMARY OF THE LOA EXPERIMENTS The Ti:Sapphire LASER Plasma density mapping by femtosecond interferometry Radiochromic film data: angular distribution of the accelerated electrons (comparison with 3-D PIC simulation) Total charge measurements Spectrum of the accelerated electron bunches (comparison with 3-D PIC simulation)

  5. LOA Ti:Sapphire PULSE DURATION fs

  6. LOA Ti:Sapphire CONTRAST RATIO fs

  7. LOA Ti:Sapphire SPECTRUM

  8. PULSE TIMING ANDINTERFEROMETRY Probe ( 30 fs ) e- Main pulse ( 30 fs ) ASE ( 10 ns ) WOLLASTON POLARIZER CCD

  9. PULSE TIMING ANDINTERFEROMETRY Probe ( 30 fs ) e- Main pulse ( 30 fs ) ASE ( 10 ns ) WOLLASTON POLARIZER CCD

  10. PROBE 50ps before the MAIN PULSE MAIN PULSE

  11. ELECTRON DENSITY PROFILE MAIN PULSE

  12. Longitudinal density profile Target shadow and fringe blurring MAIN PULSE

  13. Space Resolved Energy Spectrum of the Accelerated Electrons by Radiochromic Film Stack Detector

  14. Angular distribution of accelerated electrons and a first estimation of their energy plasma 26 mm from the plasma This is not a simulation!

  15. Simulated angular distribution This is a simulation! The pattern produced by the electrons accelerated forward on the first radiochromic film is simulated (3-D PIC) in the condition of our experiment (courtesy of Alexander Pukhov)

  16. Total charge measurement The number of high energy electrons emitted forward per shot was measured with a charge collector of aperture 7 degrees 0.2 nC per shot 109 electrons/shot

  17. High energy electron spectrum The energy spectrum obtained with a specially designed electromagnet coupled with a set of four photodiodes is compared with the spectrum given by the 3D PIC code in the same conditions (Alexander Pukhov)

  18. LWFA: 3D PIC SIMULATION A “moving window” of a 30fs Ti:Sapphire laser pulse propagating in an unhomogeneous plasma (40µm plateau decreasing both sides with scale length of 10µm) whose maximum density is 4.3x1019cm-3. The laser intensity I=3.4x1019 W/cm2 (a≈4) produces non-linear plasma waves of high amplitude dn/n ≈ a2 >> 1. A collimated beam of energetic electrons (up to 40MeV) is produced along the laser axis.

  19. LWFA: 3D PIC SIMULATION In this case the very steep density gradient makes it possible to have the resonance conditions in a very limited spatial range of the order of 10µm. The electron bunch has about the same length. The relativistic electrons do not produce an appreciable lengthening of the bunch during their propagation in the vacuum.

  20. LWFA: 3D PIC SIMULATION

  21. LWFA: 3D PIC SIMULATION

  22. e-BUNCH TEMPORAL STRUCTURE AT THE CRITICAL SURFACE According to the laser intensity and the geometry of interaction two main mechanisms can contribute to the electron injection into the overdense plasma, which are the Brunel effect (oscillating at the laser frequency) and the j x B effect (oscillating at the second harmonic of the laser).

  23. e-BUNCH LENGTH DUE TO DRIFT IN VACUUM Increase of the bunch length l due to the propagation along a distance L non relativistic case relativistic case The elongation effects of the electron bunch during the propagation in vacuum can be relevant only in the case of non relativistic electrons

  24. CONCLUSIONS The longitudinal spatial extension of an accelerated electron bunch with the innovative laser-plasma techniques depends on the specific experimental conditions in which the acceleration develops. To measure their length it is necessary to take into account the propagation from the place of production to the place of their detection. This in fact introduces a further lengthening due to their energy spread. However, this effect is negligible for relativistic electrons.

  25. D. Giulietti, M. Galimberti, A. Giulietti, L.A. Gizzi, M. Borghesi, Ph. Balcou, A. Rousse, J.Ph. Rousseau, High-energy electron beam production by femtosecond laser interactions with exploding-foil plasmas, Phys, Rev. E, Rapid. Comm., 64, 015402(R), 2001. • D. Giulietti, M. Galimberti, A. Giulietti, L.A. Gizzi, R. Numico, P. Tomassini, M. Borghesi, V. Malka, S. Fritzler, M. Pittman, K. Ta Phouc, A. Pukhov, Production of ultracollimated bunches of multi-MeV electrons produced by 35fs laser pulses propagating in exploding foil plasmas, Physics of Plasmas, 9, 3655, 2002. • P. Tomassini, A.Giulietti, L.A.Gizzi, R. Numico, M.Galimberti, D.Giulietti, M. Borghesi, Application of novel techniques for interferogram analysis to laser-plasma femtosecond probing, Laser and Particle Beams, 20, 195, 2002 • D. Giulietti, Shaped pre-formed plasmas for laser wake-field acceleration experiments, in “Atoms and Plasmas in Super-Intense Laser Fields”, edited by S.I.F., 2003. • P.Tomassini, A. Giulietti, L.A. Gizzi, M. Galimberti, D.Giulietti, M.Borghesi, O.Willi, Analyzing laser plasma interferograms with the continuous wavelet transform ridge extraction technique: the method, Applied Optics, 40, 6561-68, 2001 • A. Curcio, D. Giulietti, Laser-Plasma Acceleration and Secondary Electomagnetic Radiation, Aracne Editrice, ISBN 978-88-255-2130-6, 2019

  26. more slides

  27. E.P.W. EXCITATION BY LASER WAKE FIELD second push first push vgLASER E.P.W.

  28. ELECTRON ACCELERATION IN E.P.W. 1D MODEL  

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