Target Design Optimization Research Articles

Efficient one-dimensional turbomachinery design method based on transfer learning and Bayesian optimization

Aerodynamic optimization is a powerful approach used in turbomachinery design to shorten design cycles and reduce manual intervention. The design task is to find the optimal design variables with optimal efficiency. However, most design optimization algorithms must start from scratch for each new design task because they cannot reuse previous design experience, in contrast to human experts, who can identify a near-optimal solution based on prior design experience. To address this issue, this paper proposes a transfer optimization learning method for one-dimensional (1D) turbine aerodynamic design. It can transfer the knowledge from the samples accumulated from past design optimizations (source tasks) to accelerate the target design optimization (target task). For each task, a Gaussian process-based surrogate model is established. These models are combined by a probability weighting strategy to build an ensemble model that achieves knowledge transfer. The method is validated on a 1D design case of a single-stage turbine. The results show that, compared with other state-of-the-art optimization algorithms that do not use prior design experience, the proposed method can reduce the computational cost by more than 30% while maintaining the same aerodynamic performance. This paper demonstrates an efficient transfer optimization method for the high-nonlinear 1D turbine design problem.

Structuring Free-Standing Foils for Laser-Driven Particle Acceleration Experiments

The recent development of petawatt-class laser systems sets a focus on the development of ultra-thin free-standing targets to access enhanced particle acceleration schemes vital for future applications, such as, medical and laser-driven nuclear physics. Specific strategies are required to improve the laser-to-particle energy conversion efficiency and increase the maximum particle energy. One of the promising approaches is based on the target design optimization; either by tuning key parameters which will strongly affect the laser-matter interaction process (e.g., material, composition, density, thickness, lateral dimensions, and shape) or by using micro/nanostructures on the target surface. At ELI-NP, considerable efforts are dedicated to extend the target capabilities beyond simple planar target design and develop complex targets with tailored properties suitable for high-power laser-plasma interaction experiments, as well as for studies with gamma and positrons beams. The paper provides an overview of the manufacturing capabilities currently available within ELI-NP Targets Laboratory for providing users with certain types of solid targets, specifically micro/nanostructured gold and copper foils and microns thick, porous anodized alumina. Also, optimization studies of alternative patterns (micro/nanodots) on silicon substrate are presented for future implementation on metallic free-standing thin foils.

Overview on the target fabrication facilities at ELI-NP and ongoing strategies

Along with the development of petawatt class laser systems, the interaction between high power lasers and matter flourished an extensive research, with high-interest applications like: laser nuclear physics, proton radiography or cancer therapy. The new ELI-NP (Extreme Light Infrastructure - Nuclear Physics) petawatt laser facility, with 10PW and ∼ 1023W/cm2 beam intensity, is one of the innovative projects that will provide novel research of fundamental processes during light-matter interaction. As part of the ELI-NP facility, Targets Laboratory will provide the means for in-house manufacturing and characterization of the required targets (mainly solid ones) for the experiments, in addition to the research activity carried out in order to develop novel target designs with improved performances. A description of the Targets Laboratory with the main pieces of equipment and their specifications are presented. Moreover, in view of the latest progress in the target design, one of the proposed strategies for the forthcoming experiments at ELI-NP is also described, namely: ultra-thin patterned foil of diamond-like carbon (DLC) coated with a carbon-based ultra-low density layer. The carbon foam which behaves as a near-critical density plasma, will allow the controlled-shaping of the laser pulse before the main interaction with the solid foil. Particular emphasis will be directed towards the target's design optimization, by simulation tests and tuning the key-properties (thickness/length, spacing, density foam, depth, periodicity etc.) which are expected to have a crucial effect on the laser-matter interaction process.

Optimized beryllium target design for indirectly driven inertial confinement fusion experiments on the National Ignition Facility

For indirect drive inertial confinement fusion, Beryllium (Be) ablators offer a number of important advantages as compared with other ablator materials, e.g., plastic and high density carbon. In particular, the low opacity and relatively high density of Be lead to higher rocket efficiencies giving a higher fuel implosion velocity for a given X-ray drive; and to higher ablation velocities providing more ablative stabilization and reducing the effect of hydrodynamic instabilities on the implosion performance. Be ablator advantages provide a larger target design optimization space and can significantly improve the National Ignition Facility (NIF) [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] ignition margin. Herein, we summarize the Be advantages, briefly review NIF Be target history, and present a modern, optimized, low adiabat, Revision 6 NIF Be target design. This design takes advantage of knowledge gained from recent NIF experiments, including more realistic levels of laser-plasma energy backscatter, degraded hohlraum-capsule coupling, and the presence of cross-beam energy transfer.

Monte Carlo FLUKA code simulation for study of 68Ga production by direct proton-induced reaction

68Ga is an important radionuclide for positron emission tomography. 68Ga can be produced by the 68Zn(p,n)68Ga reaction in a common biomedical cyclotrons. To facilitate optimization of target design and study activation of materials, Monte Carlo code can be used to simulate the irradiation of the target materials with charged hadrons. In this paper, FLUKA code simulation was employed to prototype a Zn target for the production of 68Ga by proton irradiation. Furthermore, the experimental data were compared with the estimated values for the thick target yield produced in the irradiation time according to FLUKA code. In conclusion, FLUKA code can be used for estimation of the production yield.

Accelerator-Based Target Design and Optimization Driven by High-Energy Electron Beams and Proton Beams for the Analysis of Neutron Generation Characteristics

Accelerator-based target design and optimization are presented in this paper as an approach for the analysis of neutron generation and characteristics. Electron-based targets and proton-based targets driven by high-energy accelerator beams are investigated. The target plays an important role in the external neutron sources in which the target was driven by high-energy accelerator beams to generate neutrons. The optimization of target design in this work is to obtain the maximum generation of neutrons out of targets considering target material and geometry, accelerator beam energy, and beam size. A three-dimensional particle detection methodology and a surface matrix arithmetic technique were used to determine the spatial distribution of the source particles (electron and proton) and the total neutron generation from the target outer surfaces. Neutron generation and characteristics were analyzed based on the optimized targets regarding neutron spectrum, average energy, and average flux. Monte Carlo calculations were performed by using MCNPX to estimate the particle interaction inside the target and to calculate the neutrons escaping out of the target surfaces.Results in this work indicated that a high-energy (1-GeV) electron accelerator beam is capable of producing high-intensity neutron flux at the range of 1.60 × 1013 n/cm2·s of 1-mA electron. Compared to an electron accelerator beam, a proton beam (1 GeV) generates higher-intensity neutron flux at the level of 4.83 × 1013 n/cm2·s of 1-mA proton. The neutron generation ratio (neutron per incident particle escaping from the target) was computed as 0.76 neutrons per electron and 38.8 neutrons per proton for the selected targets. In the electron accelerator-based target, neutron generation was mostly through photonuclear reactions (88%), followed by prompt fission (12%). Neutron production in the target of the proton accelerator-based target was mainly due to spallation reactions (40%) and prompt fissions (48%). The optimized size of the target for the electron accelerator-based target, in terms of the volume, was about 16 times smaller than that for the proton accelerator-based target. The estimated neutron energy distribution was much narrower, with the electron accelerator target ranging from 1.0 × 10−3 to 30 MeV. In the proton accelerator target, the neutron energies ranged between 1.0 × 10−5 MeV and 1 GeV.