Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

Aurand, B.; Senje, Lovisa; Svensson, Krister; Hansson, Martin; Higginson, A.; Gonoskov, Arkady; Marklund, Mattias; Persson, Anders; Lundh, Olle; Neely, D.; McKenna, P.; Wahlström, Claes‐Göran

doi:10.1063/1.4942032

Cited by 23 publications

(11 citation statements)

References 35 publications

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“…No attempt was made to measure or mitigate spatio-temporal coupling effects 41 which, if present, would equally affect all shots. Similarly, non-uniformities in the defocused laser spot, which are known to manifest in the proton beam 42 , are presumed to affect the proton source equally for all shots. The 10 μm Au hemi was chosen as the proton source target because experience has shown it to be reliable and relatively free from instability-induced structures in the proton beam profile.…”

Section: Methodsmentioning

confidence: 99%

Anomalous material-dependent transport of focused, laser-driven proton beams

Kim

McGuffey

Gautier

et al. 2018

Sci Rep

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Intense lasers can accelerate protons in sufficient numbers and energy that the resulting beam can heat materials to exotic warm (10 s of eV temperature) states. Here we show with experimental data that a laser-driven proton beam focused onto a target heated it in a localized spot with size strongly dependent upon material and as small as 35 μm radius. Simulations indicate that cold stopping power values cannot model the intense proton beam transport in solid targets well enough to match the large differences observed. In the experiment a 74 J, 670 fs laser drove a focusing proton beam that transported through different thicknesses of solid Mylar, Al, Cu or Au, eventually heating a rear, thin, Au witness layer. The XUV emission seen from the rear of the Au indicated a clear dependence of proton beam transport upon atomic number, Z, of the transport layer: a larger and brighter emission spot was measured after proton transport through the lower Z foils even with equal mass density for supposed equivalent proton stopping range. Beam transport dynamics pertaining to the observed heated spot were investigated numerically with a particle-in-cell (PIC) code. In simulations protons moving through an Al transport layer result in higher Au temperature responsible for higher Au radiant emittance compared to a Cu transport case. The inferred finding that proton stopping varies with temperature in different materials, considerably changing the beam heating profile, can guide applications seeking to controllably heat targets with intense proton beams.

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Section: Methodsmentioning

confidence: 99%

Anomalous material-dependent transport of focused, laser-driven proton beams

Kim

McGuffey

Gautier

et al. 2018

Sci Rep

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“…This mechanism, known as target normal sheath acceleration (TNSA) 20,21 , being the most robust scheme for laser-proton acceleration and studied most widely for a variety of laser and target parameters 1,21–23 , allows for direct manipulation of collective beam parameters like pointing and divergence. Influencing the symmetry of the accelerating electron sheath has been demonstrated by shaping of the focal spot 24,25 , by introducing a laser pulse front tilt 26 , or by micro-engineering of the target surface 4,27–29 . The limitation of the lateral target size (so-called mass-limited targets with few 10 μm in diameter) has been pursued as a complementary approach confining the electron sheath.…”

Section: Introductionmentioning

confidence: 99%

All-optical structuring of laser-driven proton beam profiles

et al. 2018

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Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.

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“…Previous studies have shown that the transverse spatial profile of the sheath field on the target-rear surface has a profound influence on the angular divergence of the accelerated proton beam. Using numerical simulations it has been shown that the diameter of the resultant proton beam at the detector can be reduced, if the transverse circular area of the sheath field on the rear side of the target is increased [26]. With micromachined targets, the laser interaction not only increases α eh , but also decreases l rem as the depth of the pit increases.…”

Section: Structures On 125 μM Thick Foilsmentioning

confidence: 99%

“…Focussing of the full proton beam down to a small spot has been demonstrated in the past using curved targets [24,25]. Recently, Aurand et al have demonstrated that the spatial distribution of the hot electrons on the rear side of the target and the transverse expansion of the electric sheath field has a profound effect on the angular divergence of the accelerated protons; the proton beam divergence can be reduced if the transverse spatial distribution of the electron sheath on the rear surface of the target is increased [26]. One way to reduce it is to defocus the laser on the target [26].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Aurand et al have demonstrated that the spatial distribution of the hot electrons on the rear side of the target and the transverse expansion of the electric sheath field has a profound effect on the angular divergence of the accelerated protons; the proton beam divergence can be reduced if the transverse spatial distribution of the electron sheath on the rear surface of the target is increased [26]. One way to reduce it is to defocus the laser on the target [26]. The maximum proton energy in this case is found to be lower, as the laser intensity on the target becomes lower compared to the tight focus condition.…”

Section: Introductionmentioning

confidence: 99%

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Influence of micromachined targets on laser accelerated proton beam profiles

Dalui

Permogorov

Pahl

et al. 2018

Plasma Phys. Control. Fusion

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High intensity laser-driven proton acceleration from micromachined targets is studied experimentally in the target-normal-sheath-acceleration regime. Conical pits are created on the front surface of flat aluminium foils of initial thickness 12.5 and 3 μm using series of low energy pulses (0.5-2.5 μJ). Proton acceleration from such micromachined targets is compared with flat foils of equivalent thickness at a laser intensity of 7×10 19 W cm −2 . The maximum proton energy obtained from targets machined from 12.5 μm thick foils is found to be slightly lower than that of flat foils of equivalent remaining thickness, and the angular divergence of the proton beam is observed to increase as the depth of the pit approaches the foil thickness. Targets machined from 3 μm thick foils, on the other hand, show evidence of increasing the maximum proton energy when the depths of the structures are small. Furthermore, shallow pits on 3 μm thick foils are found to be efficient in reducing the proton beam divergence by a factor of up to three compared to that obtained from flat foils, while maintaining the maximum proton energy.

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Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

Cited by 23 publications

References 35 publications

Anomalous material-dependent transport of focused, laser-driven proton beams

Anomalous material-dependent transport of focused, laser-driven proton beams

All-optical structuring of laser-driven proton beam profiles

Influence of micromachined targets on laser accelerated proton beam profiles

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