| 1. |
- Aurand, Bastian, et al.
(author)
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A setup for studies of laser-driven proton acceleration at the Lund Laser Centre
- 2015
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In: Laser and Particle Beams. - 0263-0346. ; 33:1, s. 59-64
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Journal article (peer-reviewed)abstract
- We report on a setup for the investigation of proton acceleration in the regime of target normal sheath acceleration. The main interest here is to focus on stable laser beam parameters as well as a reliable target setup and diagnostics in order to do extensive and systematic studies on the acceleration mechanism. A motorized target alignment system in combination with large target mounts allows for up to 340 shots with high repetition rate without breaking the vacuum. This performance is used to conduct experiments with a split mirror setup exploring the effect of spatial and temporal separation between the pulses on the acceleration mechanism and on the resulting proton beam.
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| 2. |
- Desforges, F. G., et al.
(author)
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Analysis of Electron Injection in Laser Wakefield Acceleration Using Betatron Emission in Capillary Tubes
- 2015
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In: 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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Conference paper (peer-reviewed)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.
(author)
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Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
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Journal article (peer-reviewed)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.
(author)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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In: 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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Journal article (peer-reviewed)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. |
- Dromey, B, et al.
(author)
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Picosecond metrology of laser-driven proton bursts.
- 2016
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Journal article (peer-reviewed)abstract
- Tracking primary radiation-induced processes in matter requires ultrafast sources and high precision timing. While compact laser-driven ion accelerators are seeding the development of novel high instantaneous flux applications, combining the ultrashort ion and laser pulse durations with their inherent synchronicity to trace the real-time evolution of initial damage events has yet to be realized. Here we report on the absolute measurement of proton bursts as short as 3.5±0.7 ps from laser solid target interactions for this purpose. Our results verify that laser-driven ion acceleration can deliver interaction times over a factor of hundred shorter than those of state-of-the-art accelerators optimized for high instantaneous flux. Furthermore, these observations draw ion interaction physics into the field of ultrafast science, opening the opportunity for quantitative comparison with both numerical modelling and the adjacent fields of ultrafast electron and photon interactions in matter.
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| 6. |
- Hansson, Martin, et al.
(author)
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Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
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Journal article (peer-reviewed)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. |
- Jung, D, et al.
(author)
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On the analysis of inhomogeneous magnetic field spectrometer for laser-driven ion acceleration.
- 2015
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 86:3
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Journal article (peer-reviewed)abstract
- We present a detailed study of the use of a non-parallel, inhomogeneous magnetic field spectrometer for the investigation of laser-accelerated ion beams. Employing a wedged yoke design, we demonstrate the feasibility of an in-situ self-calibration technique of the non-uniform magnetic field and show that high-precision measurements of ion energies are possible in a wide-angle configuration. We also discuss the implications of a stacked detector system for unambiguous identification of different ion species present in the ion beam and explore the feasibility of detection of high energy particles beyond 100 MeV/amu in radiation harsh environments.
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| 8. |
- Senje, Lovisa
(author)
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Detector Development, Source Characterization and Novel Applications of Laser Ion Acceleration
- 2017
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Doctoral thesis (other academic/artistic)abstract
- The main focus of the work presented in this thesis is on experimental studies oflaser acceleration of protons and other positive ions from solid targets. The topic is explored from three different angles: firstly, the development of diagnostics adapted to the ion pulses, secondly, the characterization of the source of the energetic particles and, finally, the application of laser-accelerated protons for time-resolved radiolysis of glass and water.Detectors that can efficiently record ion pulse parameters, such as the energyspectrum and spatial profile, were developed and implemented. One of these instruments was a modified version of a Thomson parabola spectrometer. Apartfrom the typical ion energy spectra provided by such an instrument, this modifieddiagnostic tool can also provide spatial information on pulse properties and on thespectrum of laser light transmitted through the laser-plasma interaction. The other diagnostic system developed and employed made use of plastic scintillators as a position-sensitive detector, to record either proton pulse profiles, or in combination with a dipole magnet, to record proton energy spectra, in a multiple-use, real-time feedback set-up. Laser acceleration of ions is a highly non-linear process and therefore pulse-to-pulse fluctuations are commonly large. When developing the detectors emphasis was thus placed on either being able to extract information about as many proton pulse parameters as possible simultaneously, or on being able to record large amounts of data efficiently (>100s of acquisitions over a few hours). Both these measures can be used to reduce the influence of pulse-to-pulse variations when analysing experimental results. However, they fulfil different needs, as the repetition rates of high-power lasers used for ion acceleration vary, from many laser pulses per second to one per hour or less. To be able to control and optimize the processes that occur when energyis transferred in a plasma, from a high-intensity laser pulse to a population ofenergetic protons, it is vital to understand as much as possible about the acceleration mechanisms. The so-called sheath field, a TV/m electric field, at the back of a solid target, in which the protons are accelerated to high energies is especially interesting. This sheath has been experimentally characterized in terms of its transverse expansion and the way in which this expansion influences the resulting proton pulse profile. It was shown that for an angle of incidence between the laser pulse and the target foil of 45 degrees, the transverse expansion of the sheath is asymmetric and its magnitude depends on the amount of energy contained in the laser pulse. Considerable correlation was found between the spatial properties of the laser pulse focus, the sheath and theresulting proton pulse. By splitting the laser pulse into two parts, and focusing them to two independent foci, separated by a few m, it was possible to manipulate the shape of the sheath and thereby also the transverse divergence of the proton pulse. Finally, experiments were performed on optically probed picosecond protonpulse radiolysis of various materials, such as glass and water. This was done bysplitting each laser pulse so that one part drove an acceleration process, whilethe other part could be used as an intrinsically synchronised optical probe. The measurements were resolved in time by using a chirped optical probe pulse. It was found that exposure to a pulse of energetic protons, induced changes in the optical absorbance of the materials. Through these measurements it was also possible to obtain information about the proton pulse itself; in particular, the duration. Under the specific conditions used in that experiment and for a narrow energy bandwidth, the duration was found to be only 3.5 +-0.7 ps. Compared to most other sources of high-energy protons, these laser-generated proton pulses can deliver extreme doses (kGy) in short (picosecond) pulses close to their source. In the pulsed proton radiolysis of water, indications were found that such a high dose rate affects the yield of solvated electrons, a radiolytic species.
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| 9. |
- Senje, Lovisa, et al.
(author)
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Diagnostics for studies of novel laser ion acceleration mechanisms.
- 2014
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 85:11
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Journal article (peer-reviewed)abstract
- Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflected from and transmitted through the target and propagating in the same direction as the ion beam. Thus, the presented diagnostic constitutes a highly adaptable tool for accurately studying novel acceleration mechanisms in terms of their angular energy distribution, conversion efficiency, and plasma density evolution.
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| 10. |
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| 11. |
- Wahlström, Claes-Göran, et al.
(author)
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Supersonic jets of hydrogen and helium for laser wakefield acceleration
- 2016
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 19
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Journal article (peer-reviewed)abstract
- The properties of laser wakefield accelerated electrons in supersonic gas flows of hydrogen and helium are investigated. At identical backing pressure, we find that electron beams emerging from helium show large variations in their spectral and spatial distributions, whereas electron beams accelerated in hydrogen plasmas show a higher degree of reproducibility. In an experimental investigation of the relation between neutral gas density and backing pressure, it is found that the resulting number density for helium is ∼30% higher than for hydrogen at the same backing pressure. The observed differences in electron beam properties between the two gases can thus be explained by differences in plasma electron density. This interpretation is verified by repeating the laser wakefield acceleration experiment using similar plasma electron densities for the two gases, which then yielded electron beams with similar properties.
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