Review of Scientific Instruments最新文献

X-ray radiography is a ubiquitous diagnostic technique in high energy density (HED) physics, with point projection backlighting commonly used for characterizing static and dynamic objects at high spatial and temporal resolutions. These are typically constrained in attainable resolution by their decrease in brightness, which is a limiting factor for high-Z HED experiments, such as double-shell implosions at the National Ignition Facility (NIF) requiring MeV-scale bremsstrahlung sources at high (<50μm) resolution. Coded source imaging is a technique using multiple point-projection sources to produce multiple overlapping radiographs, which are then decoded as a function of the source positions in a process akin to coded aperture imaging. Here, we discuss a new approach to coded source generation using multiple individual small-diameter wire targets within the footprint of a defocused large-scale a0 ≃ 1 laser to produce an MeV-scale high-resolution bright combined source for x-ray radiography. We outline optimal source designs with NIF-Advanced Radiography Capability as the case study, highlight the need for iterative reconstruction decoding, and discuss the research required to demonstrate a robust physical proof-of-concept.

An experimental setup has been developed for the simultaneous measurement of the Hall coefficient (RH) and electrical conductivity (σ) of thermoelectric (TE) specimens in the temperature range of 300-700 K. The van der Pauw geometry is utilized for the RH and σ measurements. The sample holder geometry has been designed for diverse TE specimen dimensions and easy sample mounting. A special feature of the holder geometry is that the same sample can be used for other relevant thermoelectric measurements such as the Seebeck coefficient and thermal diffusivity. This minimizes measurement errors associated with compositional or doping inhomogeneities. In the absence of high temperature standard reference materials for Hall coefficient measurements, silicon samples with different doping concentrations have been used to verify the accuracy of the instrument. Additionally, the electrical conductivity data have been validated by measurements on the same samples in a calibrated setup. Repeat measurements indicate a maximum standard deviation of ±3% and ±0.5% for the RH and σ data in the studied temperature range. Furthermore, comparisons with the calibrated setup indicate deviations within ±3% for the σ data. The suitability of the measurement setup for TE specimens has been demonstrated using measurements on n-type (Mg2Sn) and p-type (Mg3Sb2) specimens with carrier concentrations in the range of 1019-1020 cm-3.

Indium seals have been used extensively in ultra-high vacuum and cryogenic applications. Typically, these seals use indium alongside or in place of other metal gaskets in stainless-steel vacuum flanges, with some custom applications for flanges sealing directly with glass (optics or tubes). Here, we present the design and performance of three pressed indium seals (99.99% In) between aluminum and 0.5 in. diameter sapphire optics and aluminum and gold coated Kovar semiconductor packages (TO-66 and TO-39). Test fixtures were designed to mimic those of future tunable diode laser spectrometers for Earth, planetary, and manned spaceflight environmental monitoring applications. Successful high-hermeticity seals [<10-10 atm cc/s (He)] were achieved for all seals formed with sufficient pressure applied to allow indium to flow between mating surfaces. The hermeticity of the seals was maintained after temperature cycling (-10 to +80 °C, 20 cycles), with the optical seals surviving extended duration tests (-55 to +85 °C, per MIL-STD-883). Semiconductor packages (TO-39) subjected to these extended tests saw a moderate increase in leak rate [∼5 × 10-9 atm cc/s (He)]; however, further testing showed that either the glass-metal package seals or the indium were affected (the sample size was too small to draw firm conclusions for future applications). Overall, these results suggest long-term survivability of indium seals for Kovar-aluminum and sapphire-aluminum interfaces [>10 years at 10-10 atm cc/s (He)], where the coefficient of thermal expansion differs by approximately four times.

A steel belt casting equipment, weighing approximately ∼6-7 tons and measuring ∼5 m in length, has been designed and developed for simulating the industrial processing of polymer films and being combined with synchrotron radiation in situ x-ray scattering measurements. Through modification of its modules, it is feasible to implement two distinct film casting modes, namely the wet and the dry casting processes. The speed of a steel belt can span from 0.5 to 8 m/min. The highest experimental temperature and drying wind speed are 300 °C and 6 m/s, respectively. All film casting parameters, such as extrusion speed, distance between die and steel belt, casting speed, temperature, and wind speed, can be adjusted independently. Especially, the control accuracy of the temperature and casting rate can reach ±0.1 °C and ±0.01 m/min, respectively. The feasibility of this equipment has been validated through in situ x-ray scattering tests at the BL10U1 industrial beamline of the Shanghai synchrotron radiation facility. With the assistance of this equipment, the understanding of the physical mechanism behind the film casting process should be improved so that the development of advanced functional polymer films.

Providing a cloud service for optical quantum computing requires stabilizing the optical system for extended periods. It is advantageous to construct a fiber-based system, which does not require spatial alignment. However, fiber-based systems are instead subject to fiber-specific instabilities. For instance, there are phase drifts due to ambient temperature changes and external disturbances and polarization fluctuations due to the finite polarization extinction ratio of fiber components. Here, we report the success of measuring squeezed light with a fiber system for 24 h. To do this, we introduce stabilization mechanics to suppress fluctuations in the fiber system and an integrated controller to automatically align the entire system. The squeezed light at a wavelength of 1545.3 nm is measured every 2 min, where automated alignments are inserted every 30 min. The squeezing levels with an average of -4.42 dB are recorded with an extremely small standard deviation of 0.08 dB over 24 h. With the technologies developed here, we can build complicated optical setups with the fiber-based system and operate them automatically for extended periods, which is promising for cloud service of quantum computation.

Image plates (IPs) are a quickly recoverable and reusable radiation detector often used to measure proton and x-ray fluence in laser-driven experiments. Recently, IPs have been used in a proton radiography detector stack on the OMEGA laser, a diagnostic historically implemented with CR-39, or radiochromic film. The IPs used in this and other diagnostics detect charged particles, neutrons, and x-rays indiscriminately. IPs detect radiation using a photo-stimulated luminescence (PSL) material, often phosphor, in which electrons are excited to metastable states by ionizing radiation. Protons at MeV energies deposit energy deeper into the IP compared with x rays below ∼20 keV due to the Bragg peak present for protons. This property is exploited to discriminate between radiation types. Doses of mono-energetic protons between 1.7 and 14 MeV are applied to IPs using the MIT linear electrostatic ion accelerator. This paper presents the results from consecutive scans of IPs irradiated with different proton energies. The PSL ratios between subsequent scans are shown to depend on proton energy, with higher energy protons having lower PSL ratios for each scan. This finding is separate from the known energy dependence in the absolute sensitivity of IPs. The results can be compared to complimentary work on x rays, showing a difference between protons and x rays, forging a path to discriminate between proton and x-ray fluence in mixed radiation environments.

We present a system for the growth of molecular films in vacuum that exhibits high versatility with respect to the choice of molecular species. These can be either evaporated from powders or injected from solutions using an electrospray system, making it possible to handle particularly large and/or fragile molecules in a controlled environment. The apparatus is equipped with a reflectance anisotropy spectroscopy system for the in situ characterization of the optical response of the films and can be directly connected to a photoelectron spectrometer without breaking the vacuum. The system is conceived for the study and characterization of porphyrin films. Here, to showcase the range of possible analyses allowed by the experimental setup and test the operation of the system, novel results are provided on electrospray deposition on highly oriented pyrolytic graphite of Zn tetraphenyl porphyrins and Zn proto porphyrins, the latter featuring fragile side groups that make deposition from solution more attractive. In situ characterization is complemented by ex situ atomic force microscopy. Thanks to this multi-technique approach, changes in the film morphology and spectroscopic response are detected and directly related to the choice of the molecular moiety and growth method.

A birdcage resonant helicon antenna is designed, mounted, and tested in the toroidal device TORPEX. The birdcage resonant antenna is an alternative to the usual Boswell or half-helical antenna designs commonly used for ∼10 cm diameter helicon sources in low temperature plasma devices. The main advantage of the birdcage antenna lies in its resonant nature, which makes it easily operational even at large scales, an appealing feature for the TORPEX device whose poloidal cross section is 40 cm in diameter. With this antenna, helicon waves are shown to be launched and sustained throughout the whole torus of TORPEX. The helicon waves can be launched at low power on a pre-existing magnetron-generated plasma with little effect on the density profiles. The birdcage antenna can also be used alone to produce plasma, which removes the constraint of a narrow range of applied magnetic fields required by the magnetron, opening the way to a new range of studies on TORPEX with the external magnetic field as a control parameter.

In photon-deficient, noncollective Thomson scattering diagnostics, filter polychromators are typically employed in the spectral analysis of Thomson-scattered signals to achieve acceptable signal-to-noise performance. Currently, the most common polychromator filter configuration employs a set of single-passband optical filters that define individual spectral channels. Here, we introduce a new spectral analysis method for Thomson scattering based on spectral filters with multiple passbands, referred to as Thomson scattering spectral multiplexing. Implementing multi-bandpass spectral filters on polychromators increases the achievable range of electron temperature measurement for a given number of filters employed. In addition, Thomson scattering spectral multiplexing reduces systematic measurement uncertainty, with fewer required spectral channels, thereby decreasing light loss from reduced optical element interactions. A multi-bandpass filter set, optimized by a genetic algorithm, has been successfully installed and tested on the Helically Symmetric eXperiment (HSX), demonstrating the benefits of the Thomson scattering spectral multiplexing method.

Two novel web apps for W7-X are introduced: Profile Cooker and Power House. They are designed to streamline the workflow of profile fitting and power balance analysis while offering a graphical user interface that works in any common browser. This allows us to compile a comprehensive database of experimental power balance results. All fitting functions available in Profile Cooker are presented and compared on the basis of example profiles. The power balance equation assumed in Power House is established and its individual terms are discussed. The main focus of the power balance analysis is on the turbulent transport coefficients. A model for quick calculation of neutral beam power deposition based on experimental profiles is presented. Neoclassical root transition poses an issue for power balance analysis due to the uncertainty of the radial electric field. A global, neoclassical simulation with the code EUTERPE is performed for a set of experimental profiles to gain an understanding of the neoclassical root transition.