Review of Scientific Instruments最新文献

Understanding the erosion of plasma facing components in fusion devices is vital, particularly for long-pulse operations. This study presents the application of synthetic optical diagnosis on the all-W WEST tokamak. The analysis reveals reflections as significant contributors to measured emission, varying across main chamber limiters and divertor targets. Reflections at divertor locations can be up to 50% of measured emission while 95% at limiter locations. Oxygen is investigated as a proxy for low-Z species and underscores the importance of reflections in interpreting optical diagnostics, especially for validating plasma-material interactions and scrape-off layer impurity transport codes. As more fusion devices adopt full metal walls, the accurate assessment of reflections will become increasingly crucial for erosion analysis and plasma control.

Soft x-ray (SX) tomography is a useful diagnostic in fusion research, and a multi-channel SX diagnostic will be installed in JT-60SA, the largest elongated tokamak in the world. However, in the SX diagnostic of JT-60SA, plasmas will be only viewed from the low field side and the upper side of plasmas; the sight lines are limited, which would be common in future devices as well as JT-60SA. This kind of limited sight lines is not preferred for SX tomography to investigate the spatial structure of magnetohydrodynamics (MHD) modes because inadequate information of plasmas makes artifacts in the reconstructed SX profiles. One of the solutions to reduce the artifacts is to employ L1 regularization, which gives the essential and sparse contributions [Kaptanoglu et al., Phys. Plasmas 30, 033906 (2023)]. In this study, as a first topic, the applicability of L1 regularization to reduce the artifacts in SX tomography with limited sight lines is investigated with traditional L2 regularization for a high beta scenario of JT-60SA where MHD modes would occur. Here, as a series of basis functions, the Fourier-Bessel series (FBS) is employed because FBS has the poloidal Fourier modes explicitly. A disadvantage of FBS is that the accurate equilibrium inside the last closed flux surface (LCFS) is needed; interior measurement such as the motional Stark effect measurement is required, which is not always available during a whole discharge. The second topic of this study is to investigate other appropriate basis functions to study the spatial structure of MHD modes in elongated tokamak plasmas. Here, we introduce Saito's Laplacian eigenfunction (LEF). Saito's LEF can be calculated if LCFS is given and the LEF is expected to show the explicit poloidal Fourier mode. Because the calculation of LCFS with magnetic measurements is a basic task of plasma operations, Saito's LEF may be used anytime. Our investigation showed that L1 regularization can strongly improve the SX tomography with the traditional L2 regularization having FBS/LEF and would be effective against other tomographic problems in fusion devices.

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.

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.

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.

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.

An objective soft x-ray flat-field spectrograph employing a laminar-type bilayer coated, varied-line-spacing, spherical grating was designed to improve the detection limit and sensitivity of soft x-ray flat-field spectrographs in a region of 250-550 eV. As a design criterion, spectral flux, SF, [Hatano et al., Appl. Opt. 60, 4993-4999 (2021)], which is proportional to the amount of optical flux incident onto a detector and correlated with detection sensitivity, was used to be maximized. To enhance reflectivity with the coating design, Au/Ni bilayer coating was investigated to optimize the incidence angle and thickness of the Ni layer. This is based on the consideration that, in an energy region of over 400 eV, refractive indices of Au (bottom layer), Ni (top layer), and vacuum are increased from the bottom to the top of the layers, and a supplemental enhancement of reflectivity can be expected by optimizing the thickness of the top layer. Thus, the thickness of Ni and the incidence angle were chosen to be 8.0 nm and 86.00°, respectively. To maintain dispersion and spectral resolution of the grating used at an incidence angle of 87.07° as previously designed, groove density was increased to 1500 lines/mm from 1200 lines/mm of our previous design. Finally, a holographic, varied-line-spacing, spherical grating was designed assuming an aspherical-wavefront-recording configuration. The numerical simulation results showed that the spectrograph employing newly designed grating with laminar-type grooves and Au/Ni bilayer coating exhibited 2-18 times higher spectral flux as well as an improved spectral resolution compared with those obtained with the previously designed gratings and spectrographs.

We present a comprehensive overview of the commissioning process and initial results of a synchrotron beamline dedicated to atomic, molecular, and optical sciences at the BL-5 undulator port of the Indus-2 synchrotron facility, Raja Ramanna Center for Advanced Technology, Indore, India. The beamline delivers a photon flux of ∼1012 photons/s with high resolving power (∼10 000) over an energy range of 6-800 eV, making it suitable for high-resolution spectroscopy in atomic, molecular, and optical science. The energy tunability from vacuum ultraviolet to soft x-ray (6-800 eV) is achieved through a varied line spacing plane grating monochromator with four gratings: very low energy (VLEG), low energy (LEG), medium energy (MEG), and high energy (HEG). These gratings cover ranges of 6-18, 15-45, 42-126, and 90-800 eV, respectively. A differential pumping system allows windowless transmission of VUV and soft x-ray photons for gas-phase spectroscopic experiments. The beamline also includes an x-ray absorption spectroscopy (XAS) station for solid samples. To demonstrate efficiency, a spectrum was recorded using all four gratings in the 6-300 eV energy range. Standard spectra of Xe and O2 verified the resolution, achieving a resolving power of 7740 with the VLEG, consistent with design specifications. XAS spectra of Cu M, C, and O K-edges were also obtained using MEG and HEG. Details on vacuum level, grating operation, and the first commissioning experiments are presented.