| 1. |
- Andreev, N. E., et al.
(författare)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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Tidskriftsartikel (refereegranskat)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. |
- Desforges, F. G., et al.
(författare)
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Analysis of Electron Injection in Laser Wakefield Acceleration Using Betatron Emission in Capillary Tubes
- 2015
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Ingår i: Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III. - : SPIE. - 1996-756X .- 0277-786X. ; 9514, s. 95140-95140
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Konferensbidrag (refereegranskat)abstract
- The dynamics of ionization-induced electron injection in the high density (similar to 1.2 x 10(19)cm(-3)) regime of Laser Wakefield Acceleration (LWFA) was investigated by analyzing betatron X-ray emission inside dielectric capillary tubes. A comparative study of the electron and betatron X-ray properties was performed for both self-injection and ionization-induced injection. Direct experimental evidence of early onset of ionization-induced injection into the plasma wave was obtained by mapping the X-ray emission zone inside the plasma. Particle-In-Cell (PIC) simulations showed that the early onset of ionization-induced injection, due to its lower trapping threshold, suppresses self-injection of electrons. An increase of X-ray fluence by at least a factor of two was observed in the case of ionization-induced injection due to an increased trapped charge compared to self-injection mechanism.
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| 3. |
- Desforges, F. G., et al.
(författare)
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Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of ionization-induced electron injection in high density (similar to 1.2 x 10(19) cm(-3)) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. (C) 2014 AIP Publishing LLC.
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| 4. |
- Desforges, F. G., et al.
(författare)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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| 5. |
- Genoud, Guillaume, et al.
(författare)
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Laser-plasma electron acceleration in dielectric capillary tubes
- 2011
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 105:2, s. 309-316
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Tidskriftsartikel (refereegranskat)abstract
- Electron beams and betatron X-ray radiation generated by laser wakefield acceleration in long plasma targets are studied. The targets consist of hydrogen filled dielectric capillary tubes of diameter 150 to 200 microns and length 6 to 20 mm. Electron beams are observed for peak laser intensities as low as 5x10(17) W/cm(2). It is found that the capillary collects energy outside the main peak of the focal spot and contributes to keep the beam self-focused over a distance longer than in a gas jet of similar density. This enables the pulse to evolve enough to reach the threshold for wavebreaking, and thus trap and accelerate electrons. No electrons were observed for capillaries of large diameter (250 mu m), confirming that the capillary influences the interaction and does not have the same behaviour as a gas cell. Finally, X-rays are used as a diagnostic of the interaction and, in particular, to estimate the position of the electrons trapping point inside the capillary.
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| 6. |
- Hansson, Martin, et al.
(författare)
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Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
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Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
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Tidskriftsartikel (refereegranskat)abstract
- The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
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| 7. |
- Ju, J., et al.
(författare)
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Analysis of x-ray emission and electron dynamics in a capillary-guided laser wakefield accelerator
- 2014
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Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:5
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:8
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
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Tidskriftsartikel (refereegranskat)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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