High Power Laser Science and Engineering
Colin Danson, Enam Chowdhury, Chris Spindloe, Jingquan Liu
Vol. 9, Issue 1, 2021
Editor(s): Colin Danson, Enam Chowdhury, Chris Spindloe, Jingquan Liu
Year: 2021
Status: Published

High Power Laser Science and Engineering is pleased to announce a special issue on Target Fabrication. The scope of this special issue is to highlight important new results and the latest developments related to target fabrication and reviews on topics related to their deployment on ultra-high-energy/power laser facilities.

Contents 8 article(s)
Mandrel degradation model of combined fast and slow processes
Yu Zhu, Zheng Liu, Famin Yu, Qiang Chen, Wei Feng, Zhanwen Zhang, and Zhigang Wang

In this paper, we report the study of degradation for a kind of ideal mandrel material called poly-α-methylstyrene based on theoretical and experimental methods. First-principles calculations reveal two types of process: depolymerization and hydrogen-transfer-induced chain scission. The energy barrier for the former (0.68–0.82 eV) is smaller than that for most of the latter (1.39–4.23 eV). More importantly, reaction rates suggest that the former is fast whereas the latter is mostly slow, which can result in a difference of 5–31 orders of magnitude at 550 K. Furthermore, a thermogravimetric experiment shows that the activation energy of 2.53 eV for degradation is between those of fast and slow processes, corresponding to the theoretical average value of multiple reaction paths. Thus, a mandrel degradation model combining fast and slow processes is established at the atomic level. Our work provides a direction for research into the key technology of target fabrication in inertial confinement fusion.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 1 010000e1 (2021)
Morphology analysis of tracks in the aerogels impacted by hypervelocity irregular particles
Ai Du, Yi Ma, Mingfang Liu, Zhihua Zhang, Guangwei Cao, Hongwei Li, Ling Wang, Peijian Si, Jun Shen, and Bin Zhou

As an attractive collector medium for hypervelocity particles, combined with outstanding physical properties and suitable compositional characteristics, SiO2 aerogel has been deployed on outer space missions and laser shock-loaded collection experiments. In this paper, impact experiments were conducted to understand the penetration process of irregular grains, irregular Al2O3 grains with two different sizes and speeds (~110 μm@7 km/s, ~251 μm@2.3 km/s) at various density silica aerogels. By classifying the shapes of projectile residues and tracks, the morphology of tracks was analyzed. It was observed that there were several kinds of typical tracks in the penetration of irregular grains, accompanied by residues with the shapes of near-sphere, polyhedron, streamlined body wedge, and rotator. The rotational behavior was demonstrated by the final status of one flake projectile as direct evidence. In addition, there was no obvious relationship between the track length and experimental parameters, which may be caused by the uncertain interaction between aerogels and irregular particles. In addition, it confirmed the existence of fragmentation, melting situation by observing the shape of the impact entrance hole. At the same time, optical coherence tomography was used to observe the detail of tracks clearly, which provided a method to characterize the tracks nondestructively.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e14 (2021)
Radial density profile and stability of capillary discharge plasma waveguides of lengths up to 40 cm
M. Turner, A. J. Gonsalves, S. S. Bulanov, C. Benedetti, N. A. Bobrova, V. A. Gasilov, P. V. Sasorov, G. Korn, K. Nakamura, J. van Tilborg, C. G. Geddes, C. B. Schroeder, and E. Esarey

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 $\mathrm{\mu} \mathrm{m}$ to 2 mm and lengths of 9 to 40 cm. To the best of the authors’ knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for $\ge$10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible to $% and their average on-axis plasma electron density to $%. These variations explain only a small fraction of laser-driven plasma wakefield acceleration electron bunch variations observed in experiments to date. Measurements of laser pulse centroid oscillations revealed that the radial channel profile rises faster than parabolic and is in excellent agreement with magnetohydrodynamic simulation results. We show that the effects of non-parabolic contributions on Gaussian pulse propagation were negligible when the pulse was approximately matched to the channel. However, they affected pulse propagation for a non-matched configuration in which the waveguide was used as a plasma telescope to change the focused laser pulse spot size.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e17 (2021)
Targets with cone-shaped microstructures from various materials for enhanced high-intensity laser–matter interactionEditors' Pick
Tina Ebert, René Heber, Torsten Abel, Johannes Bieker, Gabriel Schaumann, and Markus Roth

Targets with microstructured front surfaces have shown great potential in improving high-intensity laser–matter interaction. We present cone-shaped microstructures made out of silicon and titanium created by ultrashort laser pulse processing with different characteristics. In addition, we illustrate a process chain based on moulding to recreate the laser-processed samples out of polydimethylsiloxane, polystyrol and copper. With all described methods, samples of large sizes can be manufactured, therefore allowing time-efficient, cost-reduced and reliable ways to fabricate large quantities of identical targets.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e24 (2021)
Fabrication of large-area uniform carbon nanotube foams as near-critical-density targets for laser–plasma experiments
Pengjie Wang, Guijun Qi, Zhuo Pan, Defeng Kong, Yinren Shou, Jianbo Liu, Zhengxuan Cao, Zhusong Mei, Shirui Xu, Zhipeng Liu, Shiyou Chen, Ying Gao, Jiarui Zhao, and Wenjun Ma

Carbon nanotube foams (CNFs) have been successfully used as near-critical-density targets in the laser-driven acceleration of high-energy ions and electrons. Here we report the recent advances in the fabrication technique of such targets. With the further developed floating catalyst chemical vapor deposition (FCCVD) method, large-area ($>25\kern0.5em {\mathrm{cm}}^2$) and highly uniform CNFs are successfully deposited on nanometer-thin metal or plastic foils as double-layer targets. The density and thickness of the CNF can be controlled in the range of $1{-}13\kern0.5em \mathrm{mg}/{\mathrm{cm}}^3$ and $10{-}200\kern0.5em \mu \mathrm{m}$, respectively, by varying the synthesis parameters. The dependence of the target properties on the synthesis parameters and the details of the target characterization methods are presented for the first time.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e29 (2021)
Fabrication of disk-shaped, deuterated resorcinol/formaldehyde foam target for laser–plasma experiments
Yumi Kaneyasu, Keiji Nagai, Marilou Cadatal-Raduban, Daniil Golovin, Satoshi Shokita, Akifumi Yogo, Takahisa Jitsuno, Takayoshi Norimatsu, and Kohei Yamanoi

Resorcinol/formaldehyde (RF) foam resin is an attractive material as a low-density target in high-power laser–plasma experiments because of its fine network structure, transparency in the visible region, and low-Z element (hydrogen, carbon, and oxygen) composition. In this study, we developed disk-shaped RF foam and deuterated RF foam targets with 40–200 μm thickness and approximately 100 mg/cm3 density having a network structure from 100 nm to a few micrometers cell size. By deuteration, the polymerization rate was drastically slowed down owing to kinetic isotope effects. These targets were used in high-power laser experiments where a megaelectronvolt proton beam was successfully generated.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e31 (2021)
Deuterated polyethylene nanowire arrays for high-energy density physics
M. G. Capeluto, A. Curtis, C. Calvi, R. Hollinger, V. N. Shlyaptsev, and J. J. Rocca

The interaction of intense, ultrashort laser pulses with ordered nanostructure arrays offers a path to the efficient creation of ultra-high-energy density (UHED) matter and the generation of high-energy particles with compact lasers. Irradiation of deuterated nanowires arrays results in a near-solid density environment with extremely high temperatures and large electromagnetic fields in which deuterons are accelerated to multi-megaelectronvolt energies, resulting in deuterium–deuterium (D–D) fusion. Here we focus on the method of fabrication and the characteristics of ordered arrays of deuterated polyethylene nanowires. The irradiation of these array targets with femtosecond pulses of relativistic intensity and joule-level energy creates a micro-scale fusion environment that produced $2\times {10}^6$ neutrons per joule, an increase of about 500 times with respect to flat solid CD2 targets irradiated with the same laser pulses. Irradiation with 8 J laser pulses was measured to generate up to 1.2 × 107 D–D fusion neutrons per shot.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 2 02000e34 (2021)
Control of amorphous solid water target morphology induced by deposition on a charged surface
Alexander Bespaly, Indranuj Dey, Jenya Papeer, Assaf Shaham, Pavel Komm, Ibrahim Hadad, Gilad Marcus, and Arie Zigler

Microstructured targets demonstrate an enhanced coupling of high-intensity laser pulse to a target and play an important role in laser-induced ion acceleration. Here we demonstrate an approach that enables us to control the morphology of amorphous solid water (ASW) microstructured targets, by deposition of water vapor on a charged substrate, cooled down to 100 K. The morphology of the deposited ASW structures is controlled by varying the surface charge on the substrate and the pressure of water vapor. The obtained target is structured as multiple, dense spikes, confined by the charged area on the substrate, with increased aspect ratio of up to 5:1 and having a diameter comparable with the typical spot size of the laser focused onto the target.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 9 Issue 3 03000e37 (2021)
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