Contents 2 Issue (s), 7 Article (s)

Vol.10, Iss.3—May.1, 2022 • pp: e17- Spec. pp:

Vol.10, Iss.2—Mar.1, 2022 • pp: e11- Spec. pp:

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Vol.10, Iss.3-May..1,2022
Research Articles
Ultra-compact post-compressor on-shot wavefront measurement for beam correction at PHELIX
J. B. Ohland, U. Eisenbarth, B. Zielbauer, Y. Zobus, D. Posor, J. Hornung, D. Reemts, and V. Bagnoud
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 3 03000e18 (2022)
Vol.10, Iss.2-Mar..1,2022
Research Articles
A high-pinning-Type-II superconducting maglev for ICF target delivery: main principles, material options and demonstration models
I. V. Aleksandrova, E. R. Koresheva, and E. L. Koshelev
Nowadays, inertial confinement fusion (ICF) research related to noncontact positioning and transport of free-standing cryogenic targets is playing an increasingly important role in this field. The operational principle behind these technologies is the magnetic acceleration of the levitating target carrier (or sabot) made from Type-II, high-temperature superconductors (HTSCs). The physics of interaction among levitation, guidance and propulsion systems is based on a quantum levitation of high-pinning HTSCs in the mutually normal magnetic fields. This paper discusses current target delivery strategies and future perspectives to create different permanent magnet guideway (PMG) systems for ICF target transport with levitation. In particular, several PMG building options for optimizing both suspension and levitation of ICF targets using an HTSC-sabot will be analyzed. Credible solutions have been demonstrated for both linear and round PMGs, including the ones with a cyclotron acceleration process to realize high-running velocities of the HTSC-sabot for a limited magnetic track. Focusing on physics, we describe in detail the main aspects of the PMG building and the results obtained from computations and proof of principle experiments. High-pinning HTSC magnetic levitation promises a stable and self-controlled levitation to accelerate the ICF targets placed in the HTSC-sabots up to the required injection velocities of 200 m/s and beyond.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e11 (2022)
Research Articles
Machine-learning guided optimization of laser pulses for direct-drive implosions
Fuyuan Wu, Xiaohu Yang, Yanyun Ma, Qi Zhang, Zhe Zhang, Xiaohui Yuan, Hao Liu, Zhengdong Liu, Jiayong Zhong, Jian Zheng, Yutong Li, and Jie Zhang
The optimization of laser pulse shapes is of great importance and a major challenge for laser direct-drive implosions. In this paper, we propose an efficient intelligent method to perform laser pulse optimization via hydrodynamic simulations guided by the genetic algorithm and random forest algorithm. Compared to manual optimizations, the machine-learning guided method is able to efficiently improve the areal density by a factor of 63% and reduce the in-flight-aspect ratio by a factor of 30% at the same time. A relationship between the maximum areal density and ion temperature is also achieved by the analysis of the big simulation dataset. This design method has been successfully demonstrated by the 2021 summer double-cone ignition experiments conducted at the SG-II upgrade laser facility and has great prospects for the design of other inertial fusion experiments.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e12 (2022)
Research Articles
High repetition rate exploration of the Biermann battery effect in laser produced plasmas over large spatial regions
J. J. Pilgram, M. B. P. Adams, C. G. Constantin, P. V. Heuer, S. Ghazaryan, M. Kaloyan, R. S. Dorst, D. B. Schaeffer, P. Tzeferacos, and C. Niemann
In this paper we present a high repetition rate experimental platform for examining the spatial structure and evolution of Biermann-generated magnetic fields in laser-produced plasmas. We have extended the work of prior experiments, which spanned over millimeter scales, by spatially measuring magnetic fields in multiple planes on centimeter scales over thousands of laser shots. Measurements with magnetic flux probes show azimuthally symmetric magnetic fields that range from 60 G at 0.7 cm from the target to 7 G at 4.2 cm from the target. The expansion rate of the magnetic fields and evolution of current density structures are also mapped and examined. Electron temperature and density of the laser-produced plasma are measured with optical Thomson scattering and used to directly calculate a magnetic Reynolds number of $1.4\times {10}^4$ , confirming that magnetic advection is dominant at $\ge 1.5$ cm from the target surface. The results are compared to FLASH simulations, which show qualitative agreement with the data.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e13 (2022)
Research Articles
Monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped high-power laser glass
Huiyu Chen, Min Qian, Youkuo Chen, Xin Wang, Jingping Tang, Lei Wen, Junjiang Hu, Wei Chen, Shubin Chen, and Lili Hu
This paper investigates the monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped phosphate laser glass, which will be utilized under liquid cooling conditions for high-power laser systems. The thermal stress, interface bubbles and residual reflectivity, which are due to high-temperature casting and bonding during the monolithic edge-cladding process, are simulated and determined. The applied mould is optimized to a rectangular cavity mould, and the casting temperature is optimized to 1000°C. The resulting lower bubble density makes the mean residual reflectivity as low as 6.75 × 10-5, which is enough to suppress the amplified spontaneous emission generated in the Nd-glass disk, and the resulting maximum optical retardation is converged to 10.2–13.3 nm/cm, which is a favourable base for fine annealing to achieve the stress specification of less than or equal to 5 nm/cm. After fine annealing at the optimized 520°C, the maximum optical retardation is as low as 4.8 nm/cm, and the minimum transmitted wavefront peak-to-valley value is 0.222 wavelength (632.8 nm). An N31 elliptical disk with the size of 194 mm × 102 mm × 40 mm can be successfully cladded by the optimized monolithic edge-cladding process, whose edge-cladded disk with the size of 200 mm × 108 mm × 40 mm can achieve laser gain one-third higher than that of an N21-type disk of the same size.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e14 (2022)
Research Articles
Accurate electron beam phase-space theory for ionization-injection schemes driven by laser pulses
Paolo Tomassini, Francesco Massimo, Luca Labate, and Leonida A. Gizzi
After the introduction of the ionization-injection scheme in laser wake field acceleration and of related high-quality electron beam generation methods, such as two-color and resonant multi-pulse ionization injection (ReMPI), the theory of thermal emittance has been used to predict the beam normalized emittance obtainable with those schemes. We recast and extend such a theory, including both higher order terms in the polynomial laser field expansion and non-polynomial corrections due to the onset of saturation effects on a single cycle. Also, a very accurate model for predicting the cycle-averaged distribution of the extracted electrons, including saturation and multi-process events, is proposed and tested. We show that our theory is very accurate for the selected processes of ${\mathrm{Kr}}^{8^{+}\to {10}^{+}}$ and ${\mathrm{Ar}}^{8^{+}\to {10}^{+}}$ , resulting in a maximum error below 1%, even in a deep-saturation regime. The accurate prediction of the beam phase-space can be implemented, for example, in laser-envelope or hybrid particle-in-cell (PIC)/fluid codes, to correctly mimic the cycle-averaged momentum distribution without the need for resolving the intra-cycle dynamics. We introduce further spatial averaging, obtaining expressions for the whole-beam emittance fitting with simulations in a saturated regime, too. Finally, a PIC simulation for a laser wakefield acceleration injector in the ReMPI configuration is discussed.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e15 (2022)
Research Articles
Temporal-filtering dissipative soliton in an optical parametric oscillator
Hui Tong, Fuyong Wang, Zhipeng Qin, Guoqiang Xie, and Liejia Qian
Dissipative solitons have been realized in mode-locked fiber lasers in the theoretical framework of the Ginzburg–Landau equation and have significantly improved the pulse energy and peak power levels of such lasers. It is interesting to explore whether dissipative solitons exist in optical parametric oscillators in the framework of three-wave coupling equations in order to substantially increase the performance of optical parametric oscillators. Here, we demonstrate a temporal-filtering dissipative soliton in a synchronously pumped optical parametric oscillator. The temporal-gain filtering of the pump pulse combined with strong cascading nonlinearity and dispersion in the optical parametric oscillator enables the generation of a broad spectrum with a nearly linear chirp; consequently, a significantly compressed pulse and high peak power can be realized after dechirping outside the cavity. Furthermore, we realized, for the first time, dissipative solitons in an optical system with a negative nonlinear phase shift and anomalous dispersion, extending the parameter region of dissipative solitons. The findings may open a new research block for dissipative solitons and provide new opportunities for mid-infrared ultrafast science.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.10 Issue, 2 02000e16 (2022)