Xray Generation in Plasma Using LaserAccelerated Electrons Rahul
- Slides: 42
X-ray Generation in Plasma Using Laser-Accelerated Electrons Rahul Shah, F. Albert, R. Fitour, Taphuoc, and A. Rousse Laboratoire d’Optique Appliquée (LOA) LOA laser (similar to what we will see at NN) K.
Intense Light Fields Cause Electron Motion Along Propagation Direction Bound Atomic Optics Z+ - Light magnetic field negligable Non-linearities arise from atomic potential a 0 << 1 Relativistic Optics transverse Magnetic field causes electron moves in direction of light wave a 0 ~1 both transverse and longitudinal Non-linearities for free electrons a 0 >> 1 Relativistics harmonics, Effective force manipulates plasma longitudinal a 0~E/ω
Bright and Short-Pulse X-rays for Diffraction, Imagery, and Diagnostic ~Å 1. Ultrafast studies (femtosecond)
Bright and Short-Pulse X-rays for Diffraction, Imagery, and Diagnostic ~Å Be shell 1. Ultrafast studies (femtosecond) fuel layer x-ray (normal) 2. Phase Contrast X-rays of laser-fusion interaction phase-contrast x-ray
Bright and Short-Pulse X-rays for Diffraction, Imagery, and Diagnostic ~Å Be shell 1. Ultrafast studies (femtosecond) fuel layer x-ray (normal) 2. Phase Contrast X-rays of laser-fusion interaction z laser trapped e~10 µm electron energy simulation 1 wave 1 e- mm phase-contrast x-ray 3. Diagnostic of process (laser -wakefield acceleration) 1 A. Pukhov and J. Meyer-ter-Vehn Appl. Phys. B, 74, (2002)
Relativistic Electrons Provides Desirable X-ray Qualities Absent in Line-emission Sources x-rays solid electrons Laser on solid targets/Kα femtosecond but low-brightness laser electron Synchrotron Radiation Broad spectrum, narrow beam, electron 10 -100 picoseconds Ge. V emagnetic field m ke. V hν EX-ray γ 3/ρ ρ (radius of curvature)
Laser Wakefield Acceleration Provides Me. V-Ge. V Electrons in Millimeters laser - 10 µm - plasma + ++ +-+ + + + 100 - Ge. V/m + Electrons pushed by laser force Pulled back by ions creating plasma wave Electrons accelerated by electrostatic field, 3 orders larger than conventional
Laser Wakefield Acceleration Provides Me. V-Ge. V Electrons in Millimeters fluorescent screen 1 mm y < 1° x electron beam Experimentally simple laser - 10 µm plasma+ ++ + -+ - + -+ + + 100 -Ge. V/m + + + Various regimes; varying energies State of the art: Ge. V, tunable and monochromatic
Laser & Plasma Can Generate Low-divergence Ultrafast X-rays from Laser-Accelerated Electrons Laser overlaps accelerating electrons Light intensity causes free-electron harmonics Relativistic Harmonics
Laser & Plasma Can Generate Low-divergence Ultrafast X-rays from Laser-Accelerated Electrons Laser creates ionic cylinder Plasma field causes synchrotron radiation from accelerating electrons Synchrotron Radiation due to Plasma
Laser & Plasma Can Generate Low-divergence Ultrafast X-rays from Laser-Accelerated Electrons Relativistic Harmonics Synchrotron motion in Plasma relativistic electron Relativistic electrons collimate radiation Synchrotron radiation field ρ (radius of curvature)
Relativistic Harmonics laser a 0 << 1 plasma Relativistic Intensity results in higher order radiation transverse a 0 ~1 both transverse and longitudinal a 0 >> 1 normalized intensity longitudinal fundamental 6 th harmonic 11 th harmonic 16 th harmonic a 0=0. 01 rest electron θ (deg)
Relativistic Harmonics plasma laser a 0 << 1 Relativistic Intensity results in higher order radiation transverse a 0 ~1 both transverse and longitudinal Previously 2 nd, 3 rd reported a 0 >> 1 normalized intensity longitudinal fundamental 6 th harmonic 11 th harmonic 16 th harmonic a 0=2 rest electron θ (deg)
Relativistic Harmonics plasma laser a 0 << 1 Relativistic Intensity results in higher order radiation transverse a 0 ~1 both transverse and longitudinal a 0 >> 1 Energetic electrons result in forward peaking normalized intensity longitudinal fundamental 6 th harmonic 11 th harmonic 16 th harmonic a 0=2 1 Me. V electron copropagating θ (deg)
Relativistic Harmonics: Experimental Setup laser Laser parameters: 400 fs, 1. 053 µm, 2 J plasma
Relativistic Harmonics: Experimental Setup laser Laser parameters: 400 fs, 1. 053 µm, 2 J plasma
source image Even Harmonics Consistent with Relativistic Process laser He at a~2, linear polarization ≈5 x 1018 e-/cm-3 13 th harmonic 12 11 wavelength Signal vs. Density Relativistic harmonics Linear ne scaling, even orders Atomic harmonics ne 2 scaling, no even orders plasma
Relativistic Process Occurs with Circular Polarization laser plasma I = 5 x 1017 W cm-2 n = 1018 cm-3 Linear Pol. I = 4 x 1018 W cm-2 n = 1019 cm-3 Circular Pol. RELATIVISTIC i. Even orders ATOMIC i. Odd orders only
Relativistic Process Occurs with Circular Polarization laser plasma I = 5 x 1017 W cm-2 n = 1018 cm-3 Linear Pol. I = 4 x 1018 W cm-2 n = 1019 cm-3 Circular Pol. RELATIVISTIC i. Even orders ii. Lin/Circ polarization ATOMIC i. Odd orders only ii. Lin pol. only
Relativistic Process Occurs with Circular Polarization laser plasma I = 5 x 1017 W cm-2 n = 1018 cm-3 Linear Pol. I = 4 x 1018 W cm-2 n = 1019 cm-3 Circular Pol. 4 μm focal spot RELATIVISTIC i. Even orders ii. Lin/Circ polarization iii. Generate only at focus ATOMIC i. Odd orders only ii. Lin. pol. Only iii. Large volume of generation
Angular Profile Shows Role of Accelerated Electrons source image slit plasma laser 12 grating detector 11 wavelength Take into account energetic electrons and divergence of laser and electrons Using a 0~6 (10 x more power) order 100 harmonic radiation observed. Angular profile similarly depended on 1 Me. V electrons.
Relativistic High Harmonics 1, 2 laser plasma Laser light itself creates non-linearity in electron motion Observe characteristics in the radiation supporting relativistic harmonic generation Laser-accelerated electrons collimate radiation X-rays though would require a 0~10, and the higher harmonics have even broader angular distribution… Banerjee et. al. POP 20: 182, 2003 Taphuoc et al. PRL 91: 195001, 2003
X-ray Generation from Electron Beam Propagation in a Plasma D. Whittum. Physics of Fluids B, 4: 730, 1992 F=mωp 2 r/2 r 0 Ion channel plasma laser plasma Beam coulomb field repels ambient electrons Electron beam self charge and magnetic force cancel Synchrotron radiation 1 50 Ge. V electrons, ne~1014/cm 3, 5 -30 ke. V x-rays Ex-ray γ 2 ne r 0 amplitude 1 Esarey et. al. PRE 65, 056505, 2002 Joshi, et. al. Phys. Plas. , 9: 1845, 2002.
Laser-plasma Accelerates & Generates Synchrotron Radiation laser plasma synchrotron radiation 20 μm ion core Faure et. al. Nature 431: 541 2004 radius of curvature ~mm PIC after 2 mm propagation Matching of laser duration, spot and plasma wave creates cavity regime ke. V x-rays with 100 Me. V electrons n. C charge 106 photons/e. V 3 ke. V 100 Me. V, ne=1019 cm-3, r 0=2 µm
Laser-based Synchrotron Radiation: Experimental Setup 30 fs, 30 TW, 10 Hz laser I=3 x 1018 W/cm 2 (30 μm focus) ne~1019 cm-3 magnet x-rays electrons He 50 cm laser f=1 m laser plasma X-ray camera/phosphor
Laser-based Synchrotron Radiation: Experimental Setup • 10 shot average • Non-exponential • Plateau near 100 Me. V laser plasma
Laser-based Synchrotron Radiation: Experimental Setup laser plasma X-ray beam • Narrow (1 -2° beam) • 109 photons/shot over ke. V 20 mrad EX>3 ke. V
Broad X-ray Spectrum Measured with Crystal and Filters 30 cm x-ray spot after diffraction laser plasma ~200 μm • UPTO ~20% collection (here 1%) • Large spectrum from crystal & filters • Simple model of transverse force and linear acceleration calculates x-rays from electrons (limited specificity)
X-ray Variation with Density Matches Simulation Experiment PIC plasma • resonance consistent with mechanism • simulation (Pukhov group) matches trend • other processes (harmonics/ bremsstrahlung too weak) 150 Me. V divergence X-ray footprint (CCD) laser Electron spectrum energy 150 Me. V
Spatial Coherence Studies X-ray Source & Electron Acceleration fringes edge laser plasma Synchrotrons: Transverse beam monitoring coherence effects x-rays mechanistic detail direct imaging Thomson scattering Laser-based-synchrotron oscillations around central axis, radiation at cusps no measure of electrons in accelerator
Single Fringe of Edge Diffraction Observed (horizontal & vertical Ga. As (100) edges magnet laser plasma laser x-ray Be filtered x-ray camera electrons 0. 15 m 2 m Single shot image; vertically averaged Laser poynting causes peak position to fluctuate Δx ~ (Fresnel) (~λD Fraunhoffer) Δx ~100 µm (20 µm pixels)
Broad Spectrum Contributes to Diffraction POWER SPECTRUM laser plasma Power spectrum = source spectrum x Be x CCD camera response Be Large bandwidth washes out higher oscillations Neg. difference between spectral limits FRESNEL CALCULATION
X-rays Measure Transverse Dimension of Electrons in Plasma PIC self injection suggests full range of oscillation amplitudes plasma laser Sharp curvature – Strong emission electron beam weak curvature low emission 100 Me. V elec. 25 Me. V elec. 3 ke. V radiation Use Gaussian radial distribution of oscillation amplitudes; Synchrotron radiation emission integrated to determine linear source profile
X-rays Measure Transverse Dimension of Electrons in Plasma PIC self injection suggests full range of oscillation amplitudes energetic electrons electron profile x-ray profiles weak electrons plasma laser Sharp curvature – Hard x-rays electron beam weak curvature Soft x-rays X-rays measure upper limit of electrons Calculations from simple modeling of radiation indicate >100 Me. V electrons dominate
Experimentally < 5 μm Transverse Dimension; Simulation Shows 4 μm 4 µm laser plasma Bandwidth and pixel size limits resolution Agrees with simulation and simple modeling of radiation
Laser Based Synchrotron Radiation laser Plasma electrostatic field causes transverse oscillations and synchrotron radiation Broadband ke. V spectrum, directional femtosecond Fresnel diffraction gives < 5 μm FWHM x -ray/ electron source diameter (6 x smaller than vacuum laser-focus). Rousse, Ta. Phuoc, Shah et. al. PRL 93: 13005, 2004 Shah et. al. PRE 74, 045401(R) 2006 plasma
X-ray Generation from Laser Accelerated Electrons laser Direct relativistic scattering provides VUV-XUV at current intensities; copropagating electrons brighten source Oscillations of electrons in plasma electrostatic field generate synchrotron radiation More stable electron beams will lead to counterpropagating geometry for hard bright x-rays and eventually FELs for coherent, compact sources plasma
Acknowledgements LOA: Davidé Boschetto, Fréderic Burgy, Jean-Philippe Rousseau Budker Institute of Nuclear Physics: Oleg Shevchenko Nebraska: Donald Umstadter, Sudeep Banerjee Heinrich-Heine Universitat: Alexander Pukhov and Sergei Kiselev Funding National Science Foundation (International Fellowship) Centre Nationale de Recherche Scientifique (CNRS)
extra
Relativistic Light Scattering laser plasma
Relativistic Light Scattering laser plasma
Far-field Radiation Distribution and Source Size laser plasma Strictly sinusoidal motion would produce ~5 mrad xray beam Measured 40 mrad xray beam from combination of sinusoidal and helical trajectories.
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