Abstract:Proton beams driven by chirped pulse amplified lasers have multi-picosecond duration and can isochorically and volumetrically heat material samples, potentially providing an approach for creating samples of warm dense matter with conditions not present on Earth. Envisioned on a larger scale, they could heat fusion fuel to achieve ignition. We have shown in an experiment that a kilojoule-class, multipicosecond short pulse laser is particularly effective for heating materials. The proton beam can be focussed via… Show more
“…The 8 enhancement factor observed on the RCF suggests a discrepancy between the contaminant layers of the experiment and simulation. The contaminant layers that source the protons have proven difficult to characterize 53 , 54 , and estimates range from a few nm 55 to 1 56 , varying significantly depending on material adhesion and environmental factors 57 . Figure 3 Comparison of flat and microtube ( ) targets for the optimum laser configuration (28 J, 140 fs).…”
The interaction of an intense laser with a solid foil target can drive $$\sim$$
∼
TV/m electric fields, accelerating ions to MeV energies. In this study, we experimentally observe that structured targets can dramatically enhance proton acceleration in the target normal sheath acceleration regime. At the Texas Petawatt Laser facility, we compared proton acceleration from a $$1\, {\upmu }\hbox {m}$$
1
μ
m
flat Ag foil, to a fixed microtube structure 3D printed on the front side of the same foil type. A pulse length (140–450 fs) and intensity ((4–10) $$\times 10^{20}$$
×
10
20
W/cm$$^2$$
2
) study found an optimum laser configuration (140 fs, 4 $$\times 10^{20}$$
×
10
20
W/cm$$^2$$
2
), in which microtube targets increase the proton cutoff energy by 50% and the yield of highly energetic protons ($$>10$$
>
10
MeV) by a factor of 8$$\times$$
×
. When the laser intensity reaches $$10^{21}$$
10
21
W/cm$$^2$$
2
, the prepulse shutters the microtubes with an overcritical plasma, damping their performance. 2D particle-in-cell simulations are performed, with and without the preplasma profile imported, to better understand the coupling of laser energy to the microtube targets. The simulations are in qualitative agreement with the experimental results, and show that the prepulse is necessary to account for when the laser intensity is sufficiently high.
“…The 8 enhancement factor observed on the RCF suggests a discrepancy between the contaminant layers of the experiment and simulation. The contaminant layers that source the protons have proven difficult to characterize 53 , 54 , and estimates range from a few nm 55 to 1 56 , varying significantly depending on material adhesion and environmental factors 57 . Figure 3 Comparison of flat and microtube ( ) targets for the optimum laser configuration (28 J, 140 fs).…”
The interaction of an intense laser with a solid foil target can drive $$\sim$$
∼
TV/m electric fields, accelerating ions to MeV energies. In this study, we experimentally observe that structured targets can dramatically enhance proton acceleration in the target normal sheath acceleration regime. At the Texas Petawatt Laser facility, we compared proton acceleration from a $$1\, {\upmu }\hbox {m}$$
1
μ
m
flat Ag foil, to a fixed microtube structure 3D printed on the front side of the same foil type. A pulse length (140–450 fs) and intensity ((4–10) $$\times 10^{20}$$
×
10
20
W/cm$$^2$$
2
) study found an optimum laser configuration (140 fs, 4 $$\times 10^{20}$$
×
10
20
W/cm$$^2$$
2
), in which microtube targets increase the proton cutoff energy by 50% and the yield of highly energetic protons ($$>10$$
>
10
MeV) by a factor of 8$$\times$$
×
. When the laser intensity reaches $$10^{21}$$
10
21
W/cm$$^2$$
2
, the prepulse shutters the microtubes with an overcritical plasma, damping their performance. 2D particle-in-cell simulations are performed, with and without the preplasma profile imported, to better understand the coupling of laser energy to the microtube targets. The simulations are in qualitative agreement with the experimental results, and show that the prepulse is necessary to account for when the laser intensity is sufficiently high.
“…(d) shows example RCF layers from both shots with the experimental geometry overlaid on top. characterization of the proton radiography source with the CPC cone while also further investigating a focusing isochoric heating platform, which was recently demonstrated on the OMEGA-EP facility in McGuffey et al [21]. In this OMEGA-EP experiment, TNSA protons were focused using wedged aluminium plates onto a copper puck.…”
Proton radiography using short-pulse laser drivers is an important tool in high-energy density (HED) science for dynamically diagnosing key characteristics in plasma interactions. Here we detail the first demonstration of target-normal sheath acceleration (TNSA)-based proton radiography the NIF-ARC laser system aided by the use of compound parabolic concentrators (CPCs). The multi-kJ energies available at the NIF-ARC laser allows for a high-brightness proton source for radiography and thus enabling a wide range of applications in HED science. In this demonstration, proton radiography of a physics package was performed and this work details the spectral properties of the TNSA proton probe as well as description of the resulting radiography quality.
“…Ion stopping in warm dense matter (WDM) is an important topic in inertial confinement fusion (ICF) for the ignition of small-margin ICF targets by α -particle self-heating 1 , 2 and for ICF schemes using ion beams as the main driver, like heavy-ion fusion 3 , 4 or ion-driven fast ignition 5 , 6 . A precise knowledge of ion stopping in WDM is also essential for understanding proton transport in matter 7 , 8 and for experiments where dense plasma states are generated using ion beams 9 , in particular proton isochoric heating 10 , 11 . Such experiments have applications for studying the structure 12 , the equation-of-state 13 and the transport properties of dense plasmas 14 , like the conductivity 13 , 15 and the thermal equilibration 16 of WDM samples.…”
Ion stopping in warm dense matter is a process of fundamental importance for the understanding of the properties of dense plasmas, the realization and the interpretation of experiments involving ion-beam-heated warm dense matter samples, and for inertial confinement fusion research. The theoretical description of the ion stopping power in warm dense matter is difficult notably due to electron coupling and degeneracy, and measurements are still largely missing. In particular, the low-velocity stopping range, that features the largest modelling uncertainties, remains virtually unexplored. Here, we report proton energy-loss measurements in warm dense plasma at unprecedented low projectile velocities. Our energy-loss data, combined with a precise target characterization based on plasma-emission measurements using two independent spectroscopy diagnostics, demonstrate a significant deviation of the stopping power from classical models in this regime. In particular, we show that our results are in closest agreement with recent first-principles simulations based on time-dependent density functional theory.
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