• Knapp Hegelund posted an update 6 months, 3 weeks ago

    Coated glass targets are a key component of the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of these glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with µm thick films. In addition, nm-thin layers of Ti are used as an interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5%, being optimal for laser ablation processing. With this method, a short (few ms) and well defined pulse of impurities with about 1017 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with a velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X.We present a new collinear laser spectroscopy setup that has been designed to overcome systematic uncertainty limits arising from high-voltage and frequency measurements, beam superposition, and collisions with residual gas that are present in other installations utilizing this technique. The applied methods and experimental realizations are described, including an active stabilization of the ion-source potential, new types of ion sources that have not been used for collinear laser spectroscopy so far, dedicated installations for pump-and-probe measurements, and a versatile laser system referenced to a frequency comb. The advanced setup enables us to routinely determine transition frequencies, which was so far demonstrated only for a few cases and with lower accuracy at other facilities. It has also been designed to perform accurate high-voltage measurements for metrological applications. Demonstration and performance measurements were carried out with Ca+ and In+ ions.An increasing number of dynamic experiments, especially those involving laser drive, are employing in situ x-ray diffraction as a probe to interrogate structure evolution between states of matter under extreme pressure and temperature. We present an alternative configuration, focal construct geometry, for in situ x-ray diffraction to measure the structure and evolution of dynamically compressed polycrystalline materials on a laser platform. This configuration makes full use of the isotropically emitted He-α x rays by employing an annular (or semi-annular) collimator rather than a regular pinhole collimator and thus increases the flux of incident x rays reaching the sample as well as the intensity of the diffracted x rays, enabling the detection of a diffraction pattern with less laser energy. Its effectiveness and applicability are validated against the conventional Debye-Scherrer geometry through direct molecular dynamics simulations and x-ray diffraction simulations for two representative shock-induced phase transition events, solid-solid and solid-liquid (or melting). This configuration reproduces all the Debye-Scherrer diffraction profiles in good accuracy and demonstrates superior efficiency in utilizing the isotropic x-ray source and harvesting diffracted x rays while preserving the angular resolution.We present a method to stabilize two lasers to an optical cavity using pulsed triple frequency modulation. The setup allows simultaneous Pound-Drever-Hall stabilization, as well as independent frequency control, while removing interference terms that limit the frequency scan range and allowing for smaller modulation depths. A review of single, dual, and triple frequency modulation is also presented in addition to a discussion of how to effectively turn pulsed triple frequency modulation into independent dual frequency modulation for each laser. This method would increase the scan range to half the free spectral range.Performing atomic force microscopy (AFM) and scanning tunneling microscopy (STM) with atomic resolution under ambient conditions is challenging due to enhanced noise and thermal drift. We show the design of a compact combined atomic force and scanning tunneling microscope that uses qPlus sensors and discuss the stability and thermal drift. By using a material with a low thermal expansion coefficient, we can perform constant height measurements and achieve atomic resolution in both AFM and STM on various samples. Moreover, the design allows a wide angle optical access to the sensor and the sample that is of interest for combining with optical microscopes or focusing optics with a high numerical aperture.A combined measurement method on the basis of liquid compressibility and the characteristics of deep sea pressure compensators and pistons is proposed to solve the difficulty in measuring the large pressure of several kilometers of water depth and the small fluctuation pressure of several centimeters of water depth in ocean pressure detection. First, the working principle of the proposed method is introduced. Second, the force of piston is evaluated under static and dynamic pressure measurement conditions, and the corresponding mathematical models are established. Third, the measurement accuracy of static and dynamic pressures is analyzed. Finally, a test platform is built. The results show that the maximum dynamic pressure of 0.025 bar is realized at a pressure changing speed of 0.2 bar/s, and the small fluctuation pressure of 2.8 × 10-3 bars is realized at a pressure of 20 bars. Epalrestat solubility dmso The measurement system can track the changing ambient pressure in real time, and the measurement accuracy of the small fluctuation pressure is only related to the characteristics of the measurement system itself but not to the external large pressure. The accuracy and feasibility of the proposed method are verified. This study provides a new approach for measuring deep sea large pressure and its small fluctuation pressure.We present a comprehensive study of the frequency-dependent sensitivity for measurements of the AC elastocaloric effect by applying both exactly soluble models and numerical methods to the oscillating heat flow problem. These models reproduce the finer details of the thermal transfer functions observed in experiments, considering here representative data for single-crystal Ba(Fe1-xCox)2As2. Based on our results, we propose a set of practical guidelines for experimentalists using this technique. This work establishes a baseline against which the frequency response of the AC elastocaloric technique can be compared and provides intuitive explanations of the detailed structure observed in experiments.

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