While the rare half of the plasma bubble is accelerating for electrons, the front half of it is...
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While the rare half of While the rare half of the plasma the plasma bubble is accelerating bubble is accelerating for for electrons, the electrons, the front half of it is front half of it is decelerating. For positive ions it is decelerating. For positive ions it is just the opposite. Thus, ions just the opposite. Thus, ions trapped in the front of trapped in the front of the bubble the bubble will observe an will observe an accelerating force. accelerating force. Trapping ions with smaller weight Trapping ions with smaller weight than that of the gas-atoms generating than that of the gas-atoms generating the plasma is easier, as heavier ions will secure a the plasma is easier, as heavier ions will secure a stable, less-mobile background, while lighter ions stable, less-mobile background, while lighter ions can move without risking the stability of the can move without risking the stability of the positive background. The pictures illustrate the positive background. The pictures illustrate the acceleration of acceleration of 1 H ions in a plasma formed from a H ions in a plasma formed from a 1:1.4 atom-ratio mixture of 1:1.4 atom-ratio mixture of 1 H and H and 3 H by a very H by a very intense laser (of PW power): (a) electron density intense laser (of PW power): (a) electron density at t=320fs, (b), (c) and (d) are electron, proton at t=320fs, (b), (c) and (d) are electron, proton and tritium densities at t=854fs. Energies of the and tritium densities at t=854fs. Energies of the accelerated protons reach as high as 10-15GeV. accelerated protons reach as high as 10-15GeV. One practical problem related to One practical problem related to laser plasma accelerators of the laser plasma accelerators of the bubble regime is the bubble regime is the control of the control of the moment of electron injection. The moment of electron injection. The only practical, very recently (2006) only practical, very recently (2006) demonstrated way [8] demonstrated way [8] for this is the for this is the colliding pulse colliding pulse injection. Here we injection. Here we suggest another way of controlled suggest another way of controlled injection: A nanowire is put in the injection: A nanowire is put in the way of the laser-pulse, and when the pulse hits the way of the laser-pulse, and when the pulse hits the wire, electrons will be injected. The pictures wire, electrons will be injected. The pictures illustrate steps of such a process in terms of illustrate steps of such a process in terms of electron-density contour plots: (a) t=0.67ps, just electron-density contour plots: (a) t=0.67ps, just before the pulse hits the wire, (b) t=0.8ps right before the pulse hits the wire, (b) t=0.8ps right after the bubble passes over the wire, (c) after the bubble passes over the wire, (c) t=4.67ps, when the injected electrons are still in t=4.67ps, when the injected electrons are still in the bubble, (d) t=5.2ps, after the bubble bursts the bubble, (d) t=5.2ps, after the bubble bursts and the accelerated electrons are released. and the accelerated electrons are released. Large-scale laser-plasma wakefield computation Y. Li 1,2 , K. Németh 1,2 , B. Shen 1,2,3 , J. Bailey 1,7 , H. Shang 1,2 , R. Soliday 1,2 , R. Crowell 4 , D. Gostola4, S. Chemerisov, W. Gai 2 , 10 X.Y. Song 2 , 9 , K. C. Harkay 1,2 , J. R. Cary 5,6 , E. Frank 8 , W. Gropp 8 1 Accelerator Systems Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA 2 Argonne Accelerator Institute, Argonne National Laboratory, Argonne, IL 60439, USA 3 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, P.O. Box 800-211, Shanghai, China 4 Chemistry Division, Argonne National Laboratory, Argonne, IL 60439, USA 5 Center for Integrated Plasma Studies and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA 6 Tech-X Corporation, Boulder, Colorado 80303, USA 7 University of Alabama, Huntsville, Alabama, 35899, USA 8 Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, USA 9 Physics Department, Northern Illinois University, DeKalb, IL 60115 10 High Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA A U.S. Department of Energy laboratory managed by The University of Chicago The Advanced Photon Source is funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences Advanced Photon Source Advanced Photon Source 9700 S. Cass Ave. 9700 S. Cass Ave. Argonne, IL 60439 USA Argonne, IL 60439 USA www.aps.anl.gov www.aps.anl.gov www.anl.gov www.anl.gov Introduction: Introduction: Laser-plasma Laser-plasma accelerators [1] utilize the large accelerators [1] utilize the large electric fields generated in plasma by electric fields generated in plasma by intense lasers to accelerate electrons. Two intense lasers to accelerate electrons. Two practical implementations involve the ‘bubble practical implementations involve the ‘bubble regime’ [2] and ‘plasma channel’ [3] ones. High regime’ [2] and ‘plasma channel’ [3] ones. High energy, small energy spread and emittance (1 GeV energy, small energy spread and emittance (1 GeV energy with ~5% spread and 2mrad emittance) have energy with ~5% spread and 2mrad emittance) have been demonstrated [3]. Reproducibility of the been demonstrated [3]. Reproducibility of the demonstrated properties remains an issue. One of demonstrated properties remains an issue. One of the areas we contributed to is the understanding of the areas we contributed to is the understanding of the origins of emittance in laser-plasma the origins of emittance in laser-plasma accelerators and providing controls to it [4]. accelerators and providing controls to it [4]. Other areas we studied are: control of electron Other areas we studied are: control of electron injection in laser-plasma accelerators by a injection in laser-plasma accelerators by a nanowire [5], acceleration of ions in laser-plasma nanowire [5], acceleration of ions in laser-plasma [6], dependence of energy spread on the injection [6], dependence of energy spread on the injection circumstances [7]. circumstances [7]. ANL’s laser plasma accelerators ANL’s laser plasma accelerators This is the type [2] of laser-plasma accelerators This is the type [2] of laser-plasma accelerators we focused our studies on. we focused our studies on. In this type of accelerator, a short (~30fs) and In this type of accelerator, a short (~30fs) and intense (~14TW) laser pulse intense (~14TW) laser pulse hits a gas jet (of H hits a gas jet (of H 2 or He), instantaneously or He), instantaneously ionizes it and blows out the electrons from a ionizes it and blows out the electrons from a spherical region (the ‘bubble’) with a diameter of spherical region (the ‘bubble’) with a diameter of ~ the plasma wavelength. The positive ions remain ~ the plasma wavelength. The positive ions remain in the bubble due to their weight creating a very in the bubble due to their weight creating a very strong electric field (~50GeV/m). The bubble strong electric field (~50GeV/m). The bubble follows the motion of the laser pulse with a speed follows the motion of the laser pulse with a speed that equals with the group velocity of the laser that equals with the group velocity of the laser pulse. Electrons flow around the bubble and collide pulse. Electrons flow around the bubble and collide at its base. Electrons may get injected into the at its base. Electrons may get injected into the bubble from its base, e.g. due to a counter- bubble from its base, e.g. due to a counter- propagating weaker laser pulse [8]. The injected propagating weaker laser pulse [8]. The injected electrons will be accelerated due to the field of electrons will be accelerated due to the field of the ions in the bubble. Finally (typically in the ions in the bubble. Finally (typically in ~10ps) the laser pulse and the bubble hits through ~10ps) the laser pulse and the bubble hits through the gas jet, the bubble bursts and the accelerated the gas jet, the bubble bursts and the accelerated electrons are released. electrons are released. C ontrol R oom Am plifier #3 Am plifier #2 Pulse Stretcher O scillator Am plifier #1 Vacuum Pulse C om pressor V acuum Interaction C ham ber R adiation shielding Single-Shot D etection E-Beam D iagnostics TUHFF Laser Output 30fs, 0.6 J (20 TW) @ 10 Hz ANL CHM’s ANL CHM’s Terawatt Ultrafast High Field Facility. Laser In He Jet e - out Al Foil Magnet Scintillation Screen PMT Jet PMT Magnet Al foil Scint. screen Parabola mirror Laser beam 20 15 10 5 0 mm 20 15 10 5 0 mm -10 0 10 mm H V L=27 m m Figure 5. Transverse profile oftheelectron beam . The beam is profile isalm ostidenticalin both the vertical(V )and horizontal (H )planes Electron beam ANL/CHM’s radiolosyse experiment: Transverse e- beam profile measured at 27 mm after the jet average of 100 shots, single shot much better 6 o 20 o spectrum 20 10 0 electron energy, MeV (a) 2 o (b) 14 o Electron beam spectrum F(E) ~ exp(-E/<E>) <E>=2.3±0.3 MeV Electron pulse charge: 2-3 nC ± 15-30% Electron pulse duration: ~1-2 ps at the sample? Will be measured by EOS Dispersion is bad! 0.5 ps/cm ANL simulation: ANL simulation: Electron injection by nanowire in Electron injection by nanowire in the bubble regime the bubble regime B. Shen, Y. Li, K. Nemeth, H. Shang, B. Shen, Y. Li, K. Nemeth, H. Shang, Y.-C. Chae, R. Soliday, R. Crowell, E. Frank, W. Gropp, and J. Y.-C. Chae, R. Soliday, R. Crowell, E. Frank, W. Gropp, and J. Cary, Phys. Plasmas 14, 053115 (2007). Cary, Phys. Plasmas 14, 053115 (2007). ANL simulation: Bubble regime for ion acceleration ANL simulation: Bubble regime for ion acceleration B. Shen, Y. Li, and M. Y. Yu, and J. Cary, “Bubble regime for ion acceleration in a B. Shen, Y. Li, and M. Y. Yu, and J. Cary, “Bubble regime for ion acceleration in a laser-driven plasma,” Phys. Rev. E 76, 055402 (R) (2007). laser-driven plasma,” Phys. Rev. E 76, 055402 (R) (2007). ANL simulation: Energy spread vs. duration of injection pulse ANL simulation: Energy spread vs. duration of injection pulse J. Bailey, Y. Li, K. Nemeth, and J. Cary, J. Undergraduate Research, submitted. J. Bailey, Y. Li, K. Nemeth, and J. Cary, J. Undergraduate Research, submitted. In the colliding pulse In the colliding pulse injection, the injection, the properties of the properties of the accelerated accelerated electrons depend on the properties electrons depend on the properties of the injection pulse as well. of the injection pulse as well. Interestingly, a longer Interestingly, a longer injection injection pulse results pulse results in a much smaller in a much smaller energy energy spread than the shorter spread than the shorter ones. The picture shows energy ones. The picture shows energy ditribution of accelerated electrons ditribution of accelerated electrons as a function of as a function of location within location within the the bubble, at t=8ps (bubble close to burst), for bubble, at t=8ps (bubble close to burst), for injection pulses of 10, 30 and 50 fs duration. It injection pulses of 10, 30 and 50 fs duration. It can be seen that the energy spread greatly improves can be seen that the energy spread greatly improves with the increase of the duration of the injection with the increase of the duration of the injection pulse. The explanation of this phenomenon is still pulse. The explanation of this phenomenon is still subject of subject of investigation. investigation. ANL simulation: Laser-driven betatron oscillation in a laser-wakefie ANL simulation: Laser-driven betatron oscillation in a laser-wakefie K. Nemeth, B. Shen, Y. Li, R. Crowell, K. C. Harkay, J. R. Cary, Phys. Rev. Lett., submit K. Nemeth, B. Shen, Y. Li, R. Crowell, K. C. Harkay, J. R. Cary, Phys. Rev. Lett., submit A plasma ‘bubble’, cut A plasma ‘bubble’, cut half slightly above the half slightly above the y=0 plane as of PIC y=0 plane as of PIC simulation [9]. Light simulation [9]. Light pulse and bubble pulse and bubble propagate along x, propagate along x, light is polarized in light is polarized in z. Isodensity surfaces z. Isodensity surfaces around the injected and around the injected and accelerated electrons accelerated electrons (red) and around the (red) and around the shell of the bubble shell of the bubble (blue) are shown. (blue) are shown. ζ ζ is is the distance from the the distance from the base of the bubble, base of the bubble, along x. along x. The injected electrons move The injected electrons move in phase with the local electro- in phase with the local electro- magnetic wave. We interpret this magnetic wave. We interpret this as a result of a driven oscillator. as a result of a driven oscillator. The fundamental oscillator is the The fundamental oscillator is the betatron oscillation transverse to betatron oscillation transverse to the optical axis. This is modulated the optical axis. This is modulated by a periodic force due to the lase by a periodic force due to the lase Just as in classical mechanics, the Just as in classical mechanics, the resulting oscillation picks up the resulting oscillation picks up the periodicity of the laser. periodicity of the laser. As the laser’s phase is k As the laser’s phase is k ξ ξ , with , with ξ ξ =x-v =x-v p t, transforming the x-t pairs t, transforming the x-t pairs of the PIC trajectories with the of the PIC trajectories with the observed v observed v p phase velocity, phase velocity, Coherence of the trajectories is Coherence of the trajectories is observed. This is in accordance observed. This is in accordance with driven oscillators again, as i with driven oscillators again, as i looses memory of initial conditions looses memory of initial conditions Numerical solution of a Numerical solution of a simple simple driven oscillator model driven oscillator model reproduces reproduces the observed beam-shape the observed beam-shape and and trajectories. Shortening trajectories. Shortening the duration the duration of the laser pulse of the laser pulse reduces the reduces the emittance in the emittance in the polarization plane polarization plane significantly. Thus we significantly. Thus we explain the explain the experimentally observed experimentally observed asymmetric beam profile [10], large betatron asymmetric beam profile [10], large betatron amplitude [11], and microbunching of beam [12]. We amplitude [11], and microbunching of beam [12]. We also provide a way to cure the large emittance. also provide a way to cure the large emittance. References: References: [1] T. Tajima and J. M. Dowson, PRL 43, 267 (1979) [1] T. Tajima and J. M. Dowson, PRL 43, 267 (1979) [2] A. Pukhov et.al., Appl. Phys. B 74, 355 (2002) [2] A. Pukhov et.al., Appl. Phys. B 74, 355 (2002) [3] W. P. Leemans et.al. Nature Physics 2, 696 (2006) [3] W. P. Leemans et.al. Nature Physics 2, 696 (2006) [4] [4] K. Németh, B. Shen, Y. Li, H. Shang, K. C. Harkay, K. Németh, B. Shen, Y. Li, H. Shang, K. C. Harkay, J. R. Cary, submitted to PRL J. R. Cary, submitted to PRL [5] [5] B. Shen et.al., Phys. Plasm. 14, 053115 (2007) B. Shen et.al., Phys. Plasm. 14, 053115 (2007) [6] [6] B. Shen et.al., PRE 76, 055402(R) (2007) B. Shen et.al., PRE 76, 055402(R) (2007) [7] [7] J. Bailey, summer internship works J. Bailey, summer internship works [8] J. Faure, et.al., Nature 444, 737 (2006). [8] J. Faure, et.al., Nature 444, 737 (2006). [9] VORPAL plasma simulation code, Tech-X Corp. [9] VORPAL plasma simulation code, Tech-X Corp. [10] S. P. D. Mangles et.al., PRL 96, 215001 (2006). [10] S. P. D. Mangles et.al., PRL 96, 215001 (2006). [11] K. T. Phuoc, et.al., PRL 97, 225002 (2006). [11] K. T. Phuoc, et.al., PRL 97, 225002 (2006). [12] Y. Glinec et.al., PRL 98, 194801 (2007). [12] Y. Glinec et.al., PRL 98, 194801 (2007).
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Transcript of While the rare half of the plasma bubble is accelerating for electrons, the front half of it is...
While the rare half of the plasmaWhile the rare half of the plasmabubble is accelerating for bubble is accelerating for electrons, the front half of it is electrons, the front half of it is decelerating. For positive ions it is decelerating. For positive ions it is just the opposite. Thus, ions just the opposite. Thus, ions trapped in the front of the bubble trapped in the front of the bubble will observe an accelerating force. will observe an accelerating force. Trapping ions with smaller weight Trapping ions with smaller weight than that of the gas-atoms than that of the gas-atoms
generating the plasma is easier, as heavier ions will secure a stable, less-generating the plasma is easier, as heavier ions will secure a stable, less-mobile background, while lighter ions can move without risking the mobile background, while lighter ions can move without risking the stability of the positive background. The pictures illustrate the acceleration stability of the positive background. The pictures illustrate the acceleration of of 11H ions in a plasma formed from a 1:1.4 atom-ratio mixture of H ions in a plasma formed from a 1:1.4 atom-ratio mixture of 11H and H and 33H H by a very intense laser (of PW power): (a) electron density at t=320fs, (b), by a very intense laser (of PW power): (a) electron density at t=320fs, (b), (c) and (d) are electron, proton and tritium densities at t=854fs. Energies of (c) and (d) are electron, proton and tritium densities at t=854fs. Energies of the accelerated protons reach as high as 10-15GeV.the accelerated protons reach as high as 10-15GeV.
One practical problem related toOne practical problem related to laser plasma accelerators of the laser plasma accelerators of the
bubble regime is the control of the bubble regime is the control of the moment of electron injection. The moment of electron injection. The only practical, very recently (2006) only practical, very recently (2006) demonstrated way [8] for this is the demonstrated way [8] for this is the colliding pulse injection. Here we colliding pulse injection. Here we suggest another way of controlled suggest another way of controlled injection: A nanowire is put in the injection: A nanowire is put in the
way of the laser-pulse, and when the pulse hits the wire, electrons will be way of the laser-pulse, and when the pulse hits the wire, electrons will be injected. The pictures illustrate steps of such a process in terms of electron-injected. The pictures illustrate steps of such a process in terms of electron-density contour plots: (a) t=0.67ps, just before the pulse hits the wire, (b) density contour plots: (a) t=0.67ps, just before the pulse hits the wire, (b) t=0.8ps right after the bubble passes over the wire, (c) t=4.67ps, when the t=0.8ps right after the bubble passes over the wire, (c) t=4.67ps, when the injected electrons are still in the bubble, (d) t=5.2ps, after the bubble bursts injected electrons are still in the bubble, (d) t=5.2ps, after the bubble bursts and the accelerated electrons are released.and the accelerated electrons are released.
Large-scale laser-plasma wakefield computationY. Li1,2, K. Németh1,2, B. Shen1,2,3 , J. Bailey1,7, H. Shang1,2, R. Soliday1,2,
R. Crowell4, D. Gostola4, S. Chemerisov, W. Gai 2,10 X.Y. Song2,9, K. C. Harkay1,2, J. R. Cary5,6, E. Frank8, W. Gropp8
1Accelerator Systems Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA2Argonne Accelerator Institute, Argonne National Laboratory, Argonne, IL 60439, USA
3State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, P.O. Box 800-211, Shanghai, China4Chemistry Division, Argonne National Laboratory, Argonne, IL 60439, USA
5Center for Integrated Plasma Studies and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA6Tech-X Corporation, Boulder, Colorado 80303, USA
7University of Alabama, Huntsville, Alabama, 35899, USA8Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
9 Physics Department, Northern Illinois University, DeKalb, IL 6011510 High Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
A U.S. Department of Energy laboratory managed by The University of ChicagoThe Advanced Photon Source is funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences
Advanced Photon SourceAdvanced Photon Source9700 S. Cass Ave.9700 S. Cass Ave.Argonne, IL 60439 USAArgonne, IL 60439 USAwww.aps.anl.govwww.aps.anl.govwww.anl.govwww.anl.gov
Introduction:Introduction: Laser-plasma accelerators [1] utilize the large Laser-plasma accelerators [1] utilize the large electric fields generated in plasma by intense lasers to accelerate electric fields generated in plasma by intense lasers to accelerate electrons. Two practical implementations involve the ‘bubble regime’ [2] electrons. Two practical implementations involve the ‘bubble regime’ [2] and ‘plasma channel’ [3] ones. High energy, small energy spread and and ‘plasma channel’ [3] ones. High energy, small energy spread and emittance (1 GeV energy with ~5% spread and 2mrad emittance) have been emittance (1 GeV energy with ~5% spread and 2mrad emittance) have been demonstrated [3]. Reproducibility of the demonstrated properties remains an demonstrated [3]. Reproducibility of the demonstrated properties remains an issue. One of the areas we contributed to is the understanding of the origins issue. One of the areas we contributed to is the understanding of the origins of emittance in laser-plasma accelerators and providing controls to it [4]. of emittance in laser-plasma accelerators and providing controls to it [4]. Other areas we studied are: control of electron injection in laser-plasma Other areas we studied are: control of electron injection in laser-plasma accelerators by a nanowire [5], acceleration of ions in laser-plasma [6], accelerators by a nanowire [5], acceleration of ions in laser-plasma [6], dependence of energy spread on the injection circumstances [7].dependence of energy spread on the injection circumstances [7].
ANL’s laser plasma acceleratorsANL’s laser plasma acceleratorsThis is the type [2] of laser-plasma accelerators we focused our studies on.This is the type [2] of laser-plasma accelerators we focused our studies on.In this type of accelerator, a short (~30fs) and intense (~14TW) laser pulseIn this type of accelerator, a short (~30fs) and intense (~14TW) laser pulsehits a gas jet (of Hhits a gas jet (of H22 or He), instantaneously ionizes it and blows out the or He), instantaneously ionizes it and blows out the
electrons from a spherical region (the ‘bubble’) with a diameter of ~ the electrons from a spherical region (the ‘bubble’) with a diameter of ~ the plasma wavelength. The positive ions remain in the bubble due to their plasma wavelength. The positive ions remain in the bubble due to their weight creating a very strong electric field (~50GeV/m). The bubble follows weight creating a very strong electric field (~50GeV/m). The bubble follows the motion of the laser pulse with a speed that equals with the group velocity the motion of the laser pulse with a speed that equals with the group velocity of the laser pulse. Electrons flow around the bubble and collide at its base. of the laser pulse. Electrons flow around the bubble and collide at its base. Electrons may get injected into the bubble from its base, e.g. due to a Electrons may get injected into the bubble from its base, e.g. due to a counter-propagating weaker laser pulse [8]. The injected electrons will be counter-propagating weaker laser pulse [8]. The injected electrons will be accelerated due to the field of the ions in the bubble. Finally (typically in accelerated due to the field of the ions in the bubble. Finally (typically in ~10ps) the laser pulse and the bubble hits through the gas jet, the bubble ~10ps) the laser pulse and the bubble hits through the gas jet, the bubble bursts and the accelerated electrons are released.bursts and the accelerated electrons are released.
Control Room
Amplifier#3
Amplifier#2
PulseStretcher
Oscillator
Amplifier#1
Amplifier#1
VacuumPulse
Compressor
VacuumInteractionChamber
Radiation shielding
Single-ShotDetection
E-BeamDiagnostics
TUHFF Laser Output
30fs, 0.6 J (20 TW) @ 10 Hz
ANL CHM’s ANL CHM’s Terawatt Ultrafast High Field Facility.
Laser In
He Jet
e- out
Al Foil MagnetScintillation
Screen
PMT
Jet
PMT
MagnetAl foil
Scint. screen
Parabola mirror
Laser beam
20
15
10
5
0
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20151050mm
-10 0 10mm
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L=27 mm
Figure 5. Transverse profile of the electron beam. The beam is profile is almost identical in both the vertical (V) and horizontal (H) planes
Electron beam ANL/CHM’s radiolosyse experiment:
Transverse e- beam profile measured at 27 mm after the jet average of 100 shots, single shot much better
6o
20o
sp
ectr
um
20100
electron energy, MeV
(a) 2o
(b) 14o
Electron beam spectrumF(E) ~ exp(-E/<E>) <E>=2.3±0.3 MeV
Electron pulse charge:2-3 nC ± 15-30%
Electron pulse duration:~1-2 ps at the sample?
Will be measured by EOS
Dispersion is bad!0.5 ps/cm
ANL simulation:ANL simulation: Electron injection by nanowire in the bubble regime Electron injection by nanowire in the bubble regime B. Shen, Y. Li, K. Nemeth, H. Shang, Y.-C. Chae, R. Soliday, R. Crowell, E. Frank, W. B. Shen, Y. Li, K. Nemeth, H. Shang, Y.-C. Chae, R. Soliday, R. Crowell, E. Frank, W. Gropp, and J. Cary, Phys. Plasmas 14, 053115 (2007).Gropp, and J. Cary, Phys. Plasmas 14, 053115 (2007).
ANL simulation: Bubble regime for ion accelerationANL simulation: Bubble regime for ion accelerationB. Shen, Y. Li, and M. Y. Yu, and J. Cary, “Bubble regime for ion acceleration in a B. Shen, Y. Li, and M. Y. Yu, and J. Cary, “Bubble regime for ion acceleration in a
laser-driven plasma,” Phys. Rev. E 76, 055402 (R) (2007).laser-driven plasma,” Phys. Rev. E 76, 055402 (R) (2007).
ANL simulation: Energy spread vs. duration of injection pulseANL simulation: Energy spread vs. duration of injection pulseJ. Bailey, Y. Li, K. Nemeth, and J. Cary, J. Undergraduate Research, submitted.J. Bailey, Y. Li, K. Nemeth, and J. Cary, J. Undergraduate Research, submitted.
In the colliding pulse injection, the In the colliding pulse injection, the properties of the accelerated properties of the accelerated electrons depend on the properties electrons depend on the properties of the injection pulse as well. of the injection pulse as well. Interestingly, a longer injection Interestingly, a longer injection pulse results in a much smaller pulse results in a much smaller energy spread than the shorter energy spread than the shorter ones. The picture shows energy ones. The picture shows energy ditribution of accelerated electrons ditribution of accelerated electrons as a function of as a function of location within location within the bubble, at t=8ps (bubble close the bubble, at t=8ps (bubble close
to burst), for injection pulses of 10, 30 and 50 fs duration. It can be seen that to burst), for injection pulses of 10, 30 and 50 fs duration. It can be seen that the energy spread greatly improves with the increase of the duration of the the energy spread greatly improves with the increase of the duration of the injection pulse. The explanation of this phenomenon is still subject of injection pulse. The explanation of this phenomenon is still subject of
investigation.investigation.
ANL simulation: Laser-driven betatron oscillation in a laser-wakefield cavityANL simulation: Laser-driven betatron oscillation in a laser-wakefield cavityK. Nemeth, B. Shen, Y. Li, R. Crowell, K. C. Harkay, J. R. Cary, Phys. Rev. Lett., submittedK. Nemeth, B. Shen, Y. Li, R. Crowell, K. C. Harkay, J. R. Cary, Phys. Rev. Lett., submitted ..
A plasma ‘bubble’, cut half A plasma ‘bubble’, cut half slightly above the y=0 plane as of slightly above the y=0 plane as of PIC simulation [9]. Light pulse PIC simulation [9]. Light pulse and bubble propagate along x, and bubble propagate along x, light is polarized in z. Isodensity light is polarized in z. Isodensity surfaces around the injected and surfaces around the injected and accelerated electrons (red) and accelerated electrons (red) and around the shell of the bubble around the shell of the bubble (blue) are shown. (blue) are shown. ζζ is the distance is the distance from the base of the bubble, along from the base of the bubble, along x.x.
The injected electrons move The injected electrons move in phase with the local electro- in phase with the local electro- magnetic wave. We interpret this magnetic wave. We interpret this as a result of a driven oscillator. as a result of a driven oscillator. The fundamental oscillator is the The fundamental oscillator is the betatron oscillation transverse to betatron oscillation transverse to the optical axis. This is modulated the optical axis. This is modulated by a periodic force due to the laser.by a periodic force due to the laser.Just as in classical mechanics, the Just as in classical mechanics, the resulting oscillation picks up the resulting oscillation picks up the periodicity of the laser.periodicity of the laser.
As the laser’s phase is kAs the laser’s phase is kξξ, with, withξξ=x-v=x-vppt, transforming the x-t pairs t, transforming the x-t pairs
of the PIC trajectories with the of the PIC trajectories with the observed vobserved vpp phase velocity, phase velocity,
Coherence of the trajectories is Coherence of the trajectories is observed. This is in accordance observed. This is in accordance with driven oscillators again, as it with driven oscillators again, as it looses memory of initial conditions.looses memory of initial conditions.
Numerical solution of a simple Numerical solution of a simple driven oscillator model reproduces driven oscillator model reproduces the observed beam-shape and the observed beam-shape and trajectories. Shortening the duration trajectories. Shortening the duration of the laser pulse reduces the of the laser pulse reduces the emittance in the polarization plane emittance in the polarization plane significantly. Thus we explain the significantly. Thus we explain the experimentally observed asymmetric experimentally observed asymmetric
beam profile [10], large betatron amplitude [11], and microbunching of beam beam profile [10], large betatron amplitude [11], and microbunching of beam [12]. We also provide a way to cure the large emittance.[12]. We also provide a way to cure the large emittance.
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