| 1. |
- Andreev, N. E., et al.
(author)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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Journal article (peer-reviewed)abstract
- A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass capillary tubes up to 8 cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1-10 GV m(-1).
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| 2. |
- Burza, Matthias, et al.
(author)
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Hollow microspheres as targets for staged laser-driven proton acceleration
- 2011
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In: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 13, s. 013030-
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Journal article (peer-reviewed)abstract
- A coated hollow core microsphere is introduced as a novel targetin ultra-intense laser–matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined.This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.
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| 3. |
- Burza, Matthias, et al.
(author)
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Laser wakefield acceleration using wire produced double density ramps
- 2013
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 16:1
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Journal article (peer-reviewed)abstract
- A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximate to 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread. DOI: 10.1103/PhysRevSTAB.16.011301
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| 4. |
- Genoud, Guillaume, et al.
(author)
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Active control of the pointing of a multi-terawatt laser.
- 2011
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 82:3
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Journal article (peer-reviewed)abstract
- The beam pointing of a multi-terawatt laser wave laser is stabilized on a millisecond time scale using an active control system. Two piezo mirrors, two position sensing detectors, and a computer based optimization program ensure that both near- and far-field are stable, even during single shot operation. A standard deviation for the distribution of laser shots of 2.6 μ rad is achieved.
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| 5. |
- Genoud, Guillaume, et al.
(author)
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Increasing energy coupling into plasma waves by tailoring the laser radial focal spot distribution in a laser wakefield accelerator
- 2013
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:6
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Journal article (peer-reviewed)abstract
- By controlling the focal spot quality with a deformable mirror, we are able to show that increasing the fraction of pulse energy contained within the central part of the focal spot, while keeping the total energy and central spot size constant, significantly increases the amount of energy transferred to the wakefield: Our measurements show that the laser loses significantly more laser energy and undergoes greater redshifting and that more charge is produced in the accelerated beam. Three dimensional particle in cell simulations performed with accurate representations of the measured focal spot intensity distribution confirm that energy in the wings of the focal spot is effectively wasted. Even though self-focusing occurs, energy in the wings of the focal spot distribution is not coupled into the wakefield, emphasising the vital importance of high quality focal spot profiles in experiments. (C) 2013 AIP Publishing LLC.
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| 6. |
- Gopal, A., et al.
(author)
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MegaGauss magnetic field generation by ultra-short pulses at relativistic intensities
- 2013
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:3
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Journal article (peer-reviewed)abstract
- We report the experimental studies on megaGauss magnetic field generation using a 35 femtosecond laser at relativistic intensities. The polarization change of the self-generated harmonics was recorded to estimate the magnetic field. A parameter scan was performed by varying the input laser intensity as well as the contrast ratio. External optical probing diagnostics were performed using the second harmonic of the incident laser. Additionally, the optical transition radiation from the rear of the target was also recorded.
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| 7. |
- Ju, J., et al.
(author)
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Analysis of x-ray emission and electron dynamics in a capillary-guided laser wakefield accelerator
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:5
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Journal article (peer-reviewed)abstract
- The dynamics of electron acceleration driven by laser wakefield inside a 30.5 mm long dielectric capillary tube is analyzed using radiation emitted in the x-ray range. 3D particle-in-cell simulations, performed with parameters close to the experimental ones, show that in long plasmas, the accelerated electrons catch up and finally overrun the driving laser owing to a higher velocity of the electrons in the plasma. The electrons are then transversely scattered by the laser pulse, and penetrate the capillary wall where they generate bremsstrahlung radiation, modeled using geant4 simulations. The signature of bremsstrahlung radiation is detected using an x-ray camera, together with the betatron radiation emitted during electron acceleration in the plasma bubble. The reflection of betatron radiation from the inner capillary surface also accounts for a fraction of the observed signal on the x-ray camera. The simulation results are in agreement with the experimental ones and provide a detailed description of the electron and radiation properties, useful for the design of laser wakefield accelerators or radiation sources using long plasma media.
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| 8. |
- Ju, J., et al.
(author)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedElectrons accelerated in the nonlinear regime in a laser wakefield accelerator experience transverse oscillations inside the plasma cavity, giving rise to ultra-short pulsed x-rays, also called the betatron radiation. We show that the fluence of x-ray can be enhanced by more than one order of magnitude when the laser is guided by a 10 mm long capillary tube instead of interacting with a 2 mm gas jet. X-rays with a synchrotron-like spectrum and associated critical energy ∼ 5 keV, with a peak brightness of ∼ 1×1021 ph/s/mm2/mrad2/0.1%BW, were achieved by employing 16 TW laser pulses.
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| 9. |
- Ju, J., et al.
(author)
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Study of electron acceleration and x-ray radiation as a function of plasma density in capillary-guided laser wakefield accelerators
- 2013
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:8
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Journal article (peer-reviewed)abstract
- Laser wakefield electron acceleration in the blow-out regime and the associated betatron X-ray radiation were investigated experimentally as a function of the plasma density in a configuration where the laser is guided. Dielectric capillary tubes were employed to assist the laser keeping self-focused over a long distance by collecting the laser energy around its central focal spot. With a 40 fs, 16 TW pulsed laser, electron bunches with tens of pC charge were measured to be accelerated to an energy up to 300 MeV, accompanied by X-ray emission with a peak brightness of the order of 10 21 ph/s/mm(2)/mrad(2)/0.1%BW. Electron trapping and acceleration were studied using the emitted X-ray beam distribution to map the acceleration process; the number of betatron oscillations performed by the electrons was inferred from the correlation between measured X-ray fluence and beam charge. A study of the stability of electron and X-ray generation suggests that the fluctuation of X-ray emission can be reduced by stabilizing the beam charge. The experimental results are in good agreement with 3D particle-in-cell (PIC) simulation. (C) 2013 AIP Publishing LLC.
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| 10. |
- Mangles, S. P. D., et al.
(author)
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Controlling the spectrum of x-rays generated in a laser-plasma accelerator by tailoring the laser wavefront
- 2009
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
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Journal article (peer-reviewed)abstract
- By tailoring the wavefront of the laser pulse used in a laser-wakefield accelerator, we show that the properties of the x-rays produced due to the electron beam's betatron oscillations in the plasma can be controlled. By creating a wavefront with coma, we find that the critical energy of the synchrotronlike x-ray spectrum can be significantly increased. The coma does not substantially change the energy of the electron beam, but does increase its divergence and produces an energy-dependent exit angle, indicating that changes in the x-ray spectrum are due to an increase in the electron beam's oscillation amplitude within the wakefield.
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