| 1. |
- 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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| 2. |
- Coury, M., et al.
(author)
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Influence of laser irradiated spot size on energetic electron injection and proton acceleration in foil targets
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:7
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Journal article (peer-reviewed)abstract
- The influence of irradiated spot size on laser energy coupling to electrons, and subsequently to protons, in the interaction of intense laser pulses with foil targets is investigated experimentally. Proton acceleration is characterized for laser intensities ranging from 2 x 10(18) - 6 x 10(20) W/cm(2), by (1) variation of the laser energy for a fixed irradiated spot size, and (2) by variation of the spot size for a fixed energy. At a given laser pulse intensity, the maximum proton energy is higher under defocus illumination compared to tight focus and the results are explained in terms of geometrical changes to the hot electron injection. (C) 2012 American Institute of Physics. [doi:10.1063/1.3685615]
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| 3. |
- Coury, M., et al.
(author)
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Injection and transport properties of fast electrons in ultraintense laser-solid interactions
- 2013
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:4
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Journal article (peer-reviewed)abstract
- Fast electron injection and transport in solid foils irradiated by sub-picosecond-duration laser pulses with peak intensity equal to 4 x 10(20)W/cm(2) is investigated experimentally and via 3D simulations. The simulations are performed using a hybrid-particle-in-cell (PIC) code for a range of fast electron beam injection conditions, with and without inclusion of self-generated resistive magnetic fields. The resulting fast electron beam transport properties are used in rear-surface plasma expansion calculations to compare with measurements of proton acceleration, as a function of target thickness. An injection half-angle of similar to 50 degrees - 70 degrees is inferred, which is significantly larger than that derived from previous experiments under similar conditions. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4799726]
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| 4. |
- Gray, R. J., et al.
(author)
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Laser pulse propagation and enhanced energy coupling to fast electrons in dense plasma gradients
- 2014
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 16
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Journal article (peer-reviewed)abstract
- Laser energy absorption to fast electrons during the interaction of an ultra-intense (10(20) Wcm(-2)), picosecond laser pulse with a solid is investigated, experimentally and numerically, as a function of the plasma density scale length at the irradiated surface. It is shown that there is an optimum density gradient for efficient energy coupling to electrons and that this arises due to strong self-focusing and channeling driving energy absorption over an extended length in the preformed plasma. At longer density gradients the laser filaments, resulting in significantly lower overall energy coupling. As the scale length is further increased, a transition to a second laser energy absorption process is observed experimentally via multiple diagnostics. The results demonstrate that it is possible to significantly enhance laser energy absorption and coupling to fast electrons by dynamically controlling the plasma density gradient.
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| 5. |
- MacLellan, D. A., et al.
(author)
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Annular Fast Electron Transport in Silicon Arising from Low-Temperature Resistivity
- 2013
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In: Physical Review Letters. - 1079-7114. ; 111:9
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Journal article (peer-reviewed)abstract
- Fast electron transport in Si, driven by ultraintense laser pulses, is investigated experimentally and via 3D hybrid particle-in-cell simulations. A transition from a Gaussian-like to an annular fast electron beam profile is demonstrated and explained by resistively generated magnetic fields. The results highlight the potential to completely transform the beam transport pattern by tailoring the resistivity-temperature profile at temperatures as low as a few eV.
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| 6. |
- MacLellan, D A, et al.
(author)
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Tunable mega-ampere electron current propagation in solids by dynamic control of lattice melt.
- 2014
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In: Physical Review Letters. - 1079-7114. ; 113:18
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Journal article (peer-reviewed)abstract
- The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.
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| 7. |
- McKenna, P., et al.
(author)
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Effect of Lattice Structure on Energetic Electron Transport in Solids Irradiated by Ultraintense Laser Pulses
- 2011
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In: Physical Review Letters. - 1079-7114. ; 106:18
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Journal article (peer-reviewed)abstract
- The effect of lattice structure on the transport of energetic (MeV) electrons in solids irradiated by ultraintense laser pulses is investigated using various allotropes of carbon. We observe smooth electron transport in diamond, whereas beam filamentation is observed with less ordered forms of carbon. The highly ordered lattice structure of diamond is shown to result in a transient state of warm dense carbon with metalliclike conductivity, at temperatures of the order of 1-100 eV, leading to suppression of electron beam filamentation.
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