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Particle acceleration in plasma. By Prof. C. S. Liu Department of Physics, University of Maryland in collaboration with V. K. Tripathi, S. H. Chen, Y. Kuramitsu, L. C. Tai, S. Y. Chen, J. Wang, N. Kumar, and B. Eliasson. Cosmic ray acceleration. Magnetosphere of the Earth.
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Particle acceleration in plasma By Prof. C. S. Liu Department of Physics, University of Maryland in collaboration with V. K. Tripathi, S. H. Chen, Y. Kuramitsu, L. C. Tai, S. Y. Chen, J. Wang, N. Kumar, and B. Eliasson
Electron can be accelerated by plasma wave: Acceleration gradient of plasma wave can be large Maximum acceleration gradient limited by the wave breaking Non-relativistic wave-breaking amplitude or giving, , for SLAC on a slab !!! Relativistic wave-breaking amplitude is the Lorentz factor for plasma wave
How to generate plasma wave ?? Mode conversion Beat wave excitation with two laser pulses Raman scattering Relativistic wake plasma wave excitation by electron beam or short pulse laser
1) Mode conversion An EM wave obliquely propagates into a plasma with density gradient. + + An oscillatory current can cause space charge oscillations. EM wave → ES wave
2) Beat wave excitation • Two long laser pulses • Plasma wave excitation possible if, • Maximum saturated amplitude of the plasma wave due to relativistic mass effect Backscattering, Forward scattering, (Rosenbluth and Liu, PRL, 1972)
3) Raman Scattering by Plasma Wave Laser light: Plasma: Scattered light: Feed back Instability Current: Growth rate:
4) Relativistic wake plasma wave excitation by electron beam or short pulse laser Maximum electric field of the plasma wave
Acceleration of a SLAC electron beam Demonstration of acceleration in beam driven wakefield (SLAC) Hogan et.al. Phys. Rev. Lett. 95, 054802 (2005)
Mono-energetic electron beam by short pulse laser Observation of mono-energetic beam of electrons with energy 50-170 MeV by three groups. Mangles et.al, Nature, 431, 535 (2004), Faure et.al., Nature, 431, 541 (2004), Geddes et.al., Nature, 431, 538 (2004)
First direct measurement of acceleration gradient; eE=2.5 GeV/m ~ 103 of linac. Chen, et.al.(Particle accelerator group, Academia Sinica, NCU)
Laser wakefield acceleration and ion channel formation in laser Micro magnetosphere Relativistic self focusing Laser power, where Relativistic dielectric constant Relativistic effect increases Ponderomotive effect decreases Resultant effect ion channel formation
Experiments at Academia Sinica (PRL, 2006) OOPIC (object-oriented particle-in-cell) code two spatial and three velocity components pre-ionized electron-proton plasma linearly polarized Gaussian laser pulse s-polarization (normal to the density perturbation) moving window immobile ions Parameters Peak laser intensity: I0 = 8x1018 W/cm2(a0 = 2.) Laser wavelength: l = 0.81mm Pulse duration: t = 45 fs Gas density:n = 4x1019/cm3(wp/wL = 0.15) Initial waist size: w0 = 4mm Chirp bandwidth: 27 nm Injection and acceleration of mono-energetic electrons by a self-modulated laser pulse
Time = 1.1 ps 50 MeV mono energetic electron beam
The wake field bunches the electrons in real space. Time = 1.1 ps
The modulated laser field traps electrons and push electrons moving with the laser pulse. Time = 1.1 ps
The modulated laser field traps electrons and push electrons moving with the laser pulse. (The plasma is turned off at time = 1.33 ps) Time = 1.43 ps 50 MeV mono energetic electron beam Ez of laser pulse
Ey u- u+ Bz kx Weibel instability Growth rate:
Outline • Plasma universe • Plasma wave excitation and trapping of resonant electrons • Laser driven acceleration and production of the mono-energetic electrons beam • Ion acceleration • Concluding remark
Plasma universe Plasma dominated universe Three minutes after Big Bang ----- Radio jets, X-ray sources, g-ray bursts, pulsar, accretion disk etc…. We observe our universe mostly by EM waves. Its dispersion relation,