Review of Scientific Instruments最新文献

We present a design and first use of a kJ level laser facility for research of non-local thermodynamic equilibrium atomic physics using the buried layer target method. The target design included a metal layer buried inside a plastic tamper with thicknesses tailored to the expected laser intensities. The target was illuminated from each side by two laser beams with intensities of 0.5-5 × 1014 W/cm2. The advanced diagnostic suite included static and time-resolved imagers and spectrometers with various spectral resolutions. A 3D printed dual elliptically curved spectrometer is presented, and its results are compared to a traditional crystal spectrometer. Experimental results and radiation hydrodynamic simulations demonstrate that the target achieved the desired thermodynamic conditions of ne ≈ 1021-1022 cm-3 and Te ≈ 1-2 keV.

Aiming at predefined-time synchronization for chaotic systems, a new predefined-time sliding mode control method is proposed. First, based on the definition of predefined-time stability, a novel predefined-time inequality is proposed, along with a detailed mathematical proof. This inequality differs from existing Lyapunov inequalities and offers greater flexibility. Second, a new sliding mode surface and sliding mode controller are proposed based on this inequality. Since the sliding mode controller introduced in this paper is tunable, the actual convergence time can be adjusted freely within the predefined time. Finally, two sets of numerical simulations demonstrate that the proposed method offers advantages in terms of short synchronization time and high regulatory performance compared to traditional predefined-time sliding mode control, finite-time sliding mode control, and fixed-time sliding mode control.

A waveguide branch-line crossover with broad bandwidth is designed for beam-forming networks in millimeter wavebands. To realize the power coupling between two parallel branch lines, a substrate with metal gratings patched replaces the common E-plane waveguide wall. Compared with the traditional crossover with coupling vias, the metal gratings achieve continuous and efficient power coupling, endowing the proposed crossover with advantages in compactness and broad bandwidth. A simulation-assisted transfer-matrix approach is used to rapidly estimate and optimize the parameters of the crossover. The coupling obtained from the simulation is over -0.5 dB from 32.1 to 39.1 GHz, with isolation greater than 15 dB and reflection less than -20 dB. A prototype is fabricated, and the measurement results agree with the simulation results, demonstrating that the proposed crossover is a promising candidate for millimeter-wave beamforming networks.

High purity silicon is considered as the test mass material for future cryogenic gravitational-wave detectors, in particular Einstein Telescope-low frequency and LIGO Voyager [(LIGO) Laser Interferometer Gravitational-Wave Observatory]. To reduce the thermal noise of the test masses, it is necessary to study the sources of corresponding losses. Mechanical resonators with frequencies 300 Hz-6 kHz are successfully used for studying, for example, losses in optical coatings of the test mass. However, the frequency range of the interferometric gravitational-wave detectors starts at 10 Hz, and the investigation of different dissipation mechanisms for the test masses in the low-frequency region is relevant. We developed a design of a four-spiral mechanical resonator for studying dissipation and noise in the low frequency range. The resonator was fabricated of a 3-in. silicon wafer using an anisotropic wet etching technique. It consists of four spiral cantilevers on a common base, linked together with additional coupling beams for increasing the frequency difference between the resonator normal modes corresponding to the fundamental flexural off-plane mode of a single spiral cantilever. The measured Q-factor of the 62 Hz out-of-phase mode of the four-spiral silicon resonator at room temperature is limited mainly by the thermoelastic loss. At 123 K, the measured Q = (1.5 ± 0.3) × 107. The main contribution to the total loss comes from clamping and surface losses.

Massive material injections in the JET tokamak have been observed to substantially affect resistive bolometer measurements, resulting in a spurious radiated power signal proportional to the quantity injected and reaching up to 8 MW. These bolometers are calibrated and designed to operate in near vacuum but certain scenarios requiring large gas injections can push the neutral pressure past nominal values. This study demonstrates that the bolometry measurement can be affected at neutral pressures above 0.1 Pa following injections with standard gas valves, shattered pellet injections, and particularly massive gas injections. The power measurement of resistive bolometers is based on the temperature difference between a measurement sensor exposed to radiation and a shielded reference sensor. We employ a thermal conductivity model to demonstrate that the conduction through the gas and the distinct geometries between the sensors can affect their cooling efficiency. This additional cooling pathway, coupled with the Joule heating from the applied voltage causes the equilibrium temperatures of the sensors to diverge. Being the very basis of the measure, this temperature difference induces a signal that is erroneously interpreted as radiated power. Experiments show large discrepancies in the response to neutral pressure among bolometer channels, attributed to variations in channel physical parameters. Nonetheless, the modeled total radiated power reproduces the experimental measurements within an order of magnitude, affirming the sensitivity of resistive bolometers to neutral pressure and gas species.

The need to optimize size, weight, and power of high-power microwave (HPM) systems has motivated the development of solid-state HPM sources, such as nonlinear transmission lines (NLTLs), which utilize gyromagnetic precession or dispersion to generate RF. One recent development implemented the NLTL as a pulse forming line (PFL) to form a nonlinear pulse forming line (NPFL) system that substantially reduced the system's size by eliminating the need for a separate PFL; however, matching standard loads can be challenging. This paper describes the development of a tapered NPFL using an exponentially tapered composite based ferrite core containing 60% nickel zinc ferrite (by volume) encased in polydimethylsiloxane (PDMS) and encapsulated in a 5% barium strontium titanate shell. The tapers exponentially change the line's impedance from a 50 Ω standard HN connection to 25 Ω before tapering back to 50 Ω. We characterized the core behavior by obtaining magnetization curves and ferromagnetic resonance measurements. The rise time (10%-90%) of the pulse decreased from ∼6 ns for 5 kV charging voltage to 1.8 ns for 15 kV charging voltage. Under unbiased conditions, the system generated HPM with a center frequency of ∼850 MHz with a 3 dB bandwidth of 125 MHz. Magnetic biases of 15 and 25 kA/m increased the modulation depth and decreased the center frequency to ∼500 MHz for 15 kV charging voltage.

We describe the design and performance of a magnetic bottle electron spectrometer (MBES) for high-energy electron spectroscopy. Our design features a 2 m long electron drift tube and electrostatic retardation lens, achieving sub-electronvolt (eV) electron kinetic energy resolution for high energy (several hundred eV) electrons with a close to 4π collection solid angle. A segmented anode electron detector enables the simultaneous collection of photoelectron spectra in high resolution and high collection efficiency modes. This versatile instrument is installed at the time-resolved molecular and optical sciences instrument at the Linac Coherent Light Source x-ray free-electron laser (XFEL). In this paper, we demonstrate its high resolution, collection efficiency, and spatial selectivity in measurements where it is coupled to an XFEL source. These combined characteristics are designed to enable high-resolution time-resolved measurements using x-ray photoelectron, absorption, and Auger-Meitner spectroscopy. We also describe the pervasive artifact in MBES time-of-flight spectra that arises from a periodic modulation in electron collection efficiency and present a robust analysis procedure for its removal.

This paper presents a magnetically isolated gate driver for the fast switching of IGBT (Insulated Gate Bipolar Transistor) in compact pulsed power sources with sharp rising edges and flat-top pulses for the application of electromagnetic launch and food processing. The proposed gate driver is implemented based on a planar transformer with a half-turn winding arrangement to increase the amplitude of the driving voltage pulse. With the half-turn winding arrangement, the leakage inductance of transformers decreases by 31.1% compared to the interleaving structure. This decrease enables a fast rise time of the driving voltage pulse. Furthermore, the gate drivers are used to drive the IGBT switching a Blumlein pulse forming network. The results show that the di/dt of the applied commercially available Si IGBT is about 10.10 A/ns with a gate voltage of 50 V and a gate capacitance charging time of about 88 ns, proving the effectiveness of the gate driver and providing a high-performance driving scheme for the fast switching of Si IGBT.

Betatron x rays from a laser wakefield accelerator provide a new avenue for high-resolution, high-throughput radiography of solid materials. Here, we demonstrate the optimization of betatron x rays for three-dimensional tomography of defects in additively manufactured (AM) alloys at a repetition rate of 2.5 Hz. Using the Advanced Laser Light Source in Varennes, Qc, we characterized the x-ray energy spectrum, spatial resolution, beam stability, and emission length from three different gas targets {He, N2, and He-N2 [He (99.5%) + N2 (0.5%)] mixture} to determine the conditions for optimized imaging resolution with minimized acquisition time. Mixed He-N2 produced the highest x-ray critical energy (19 ± 5) keV and average brightness (∼3.3×1010 photons/s/mm2/mrad2/0.1% BW) vs pure N2 gas (12 ± 4 keV and ∼1.6×1010 photons/s/mm2/mrad2/0.1% BW). The mixed gas demonstrated the best beam stability and pointing compared to pure He gas. The optimization of betatron sources at 2.5 Hz for high-resolution imaging of micrometer-scale defects in AM alloys will enable high-throughput data collection, accelerating the characterization of complex mechanical deformation processes in these materials.

Recent fusion breakeven [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)] in the National Ignition Facility (NIF) motivates an integrated approach to data analysis from multiple diagnostics. Deep neural networks provide a seamless framework for multi-modal data fusion, automated data analysis, optimization, and uncertainty quantification [Wang et al., arXiv:2401.08390 (2024)]. Here, we summarize different neural network methods for x-ray and neutron imaging data from NIF. To compensate for the small experimental datasets, both model based physics-informed synthetic data generation and deep neural network methods, such as generative adversarial networks, have been successfully implemented to allow a variety of automated workflows in x-ray and neutron image processing. We highlight results in noise emulation, contour analysis for low-mode analysis and asymmetry, denoising, and super-resolution. Further advances in the integrated multi-modal imaging, in sync with experimental validation and uncertainty quantification, will help with the ongoing experimental optimization in NIF, as well as the maturation of alternate inertial confinement fusion (ICF) platforms such as double-shells.