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A newly developed instrument comprising a near ambient pressure (NAP) photoemission electron microscope (PEEM) and a tunable deep ultraviolet (DUV) laser source is described. This NAP-PEEM instrument enables dynamic imaging of solid surfaces in gases at pressures up to 1 mbar. A diode laser (976 nm) can illuminate a sample from the backside for in situ heating in gases up to 1200 K in minutes. The DUV laser with a tunable wavelength between 175 nm and 210 nm is perpendicularly incident onto the sample surface for PEEM imaging of a wide spectrum of solids with different surface work functions. Using this setup, we have first demonstrated spatiotemporal oscillation patterns of CO oxidation reaction on Pt(110) from high vacuum to NAPs and gas-induced restructuring of metal nanostructures in millibar gases. The new facility promises important applications in heterogeneous catalysis, electrochemical devices, and other surface processes under nearly working conditions.Power sources play an important role in the characteristics and the applications of the electrothermal (ET) plasma as an edge localized mode (ELM) heat flux simulator. A repetitive high current ET plasma source with the capability of working at a 10 Hz repetition rate and peak current 7.5 kA is presented in this paper. By controlling the sequence of discharge of ten pulse power modules, a repetitive high heat flux plasma jet can be generated. A two-stage capillary structure is presented, and its repetitive trigger driving circuit based on surface flashover ignition is designed to achieve reliable and repetitive discharge. The topology of the inductive and capacitive (LC) series resonant circuit is applied to the charging system of the pulsed power source. Wnt inhibitors clinical trials The charging current is limited to 500 A with a charging time of 3.5 ms, and the ratio of the charging voltage to the operating voltage is 1.85. A diode and a power resistor in series are used to suppress the negative overvoltage, which is helpful to increase the thyristors' operating reliability. Using the designed repetitive ET plasma source, the characteristics of the ET plasma jet are investigated by measuring the voltages and currents and by obtaining images of the discharges. Experimental results show that the repetitive ET plasma generator can be used as an appropriate way to simulate the ELM-like heat flux plasma.A rail-gap switch with a multistep triggering system was developed. The rail-gap switch consisted of two rail-like electrodes and a knife-edge electrode parallel to each other. It was assembled from many pieces and filled with unpressurized-flowing dry air. Good alignments between all electrodes were achieved by using a special jig and the knife-edge electrode as the spatial reference. Furthermore, to trigger the rail-gap switch, a multistep triggering system was used. The triggering system consisted of three components an optical trigger-pulse generator, a slow high-voltage trigger-pulse generator using an ignition coil for a car, and finally, a fast high-voltage trigger-pulse generator using a three-stage Marx generator. The triggering system generated a negative high-voltage trigger pulse of less than -40 kV with a falling speed of -6.6 ± 0.4 kV/ns. The falling speed was fast enough to initiate multichannel discharges in the rail-gap switch. Finally, the rail-gap switch was tested using a test bench consisting of a 0.5-μF capacitor bank charged to 20 kV. The rail-gap switch was triggered by the multistep triggering system robustly with a delay of 180 ns. The delay between the time, when the peak current of the test bench occurred, and the trigger pulse was 890 ns with a jitter of 20 ns, i.e., ∼2% uncertainty in time. The inductance of the rail-gap switch was ∼80 nH obtained from the discharge tests. The rail-gap switch with the multistep high-voltage triggering system is suitable for any pulsed-power systems with current rise times in the order of 1 µs.A 3 MeV proton radio frequency quadrupole (RFQ) accelerator has been designed, built, and commissioned at the Bhabha Atomic Research Centre, India. A compact wide bandwidth strip-line fast Faraday cup (SFFC) has been developed for the beam bunch measurements of the 352 MHz RFQ. The SFFC design is improvised over the standard strip-line FFC designs with a thicker strip, which can withstand larger beam intensities. The absence of the pinhole beam limiting aperture and the provision for a suppressor electrode to suppress secondary electrons on the strip are other improvisations over standard SFFC designs. The SFFC has been characterized using the time domain reflectometry method, and a broad bandwidth of ∼7 GHz is measured. The SFFC has been tested with a 3 MeV RFQ beam at a 4 mA peak current. The time structure of the individual micro-pulses with a FWHM of 297 ps has been measured with a SFFC.A high accuracy variable beam entrance Faraday cup (VBEFC) system is designed in this work. The presented VBEFC system is designed for the beam current profile measurement of the transient hollow cathode discharge (THCD) generated pulsed electron beam, which is a new source of high energy flux for metallic material processing. By proper designs of the beam entrance array, fast response electron collector, grounding, and shielding, this VBEFC system is capable of determining the radial profile and its temporal evolution of the THCD generated electron beam. The results of the electron beam current and current density distributions collected at varying radial locations and times under multiple voltages are presented in this paper. The experimental results show that both the amplitude and the current density of the THCD electron beam at a given radius always increased with the increase in the accelerating voltage, which is coincident with the self-focused propagation of the electron beam promoted by the voltage.The active manipulation of nuclear spins with radio-frequency (RF) coils is at the heart of nuclear magnetic resonance (NMR) spectroscopy and spin-based quantum devices. Here, we present a miniature RF transmitter designed to generate strong RF pulses over a broad bandwidth, allowing for fast spin rotations on arbitrary nuclear species. Our design incorporates (i) a planar multilayer geometry that generates a large field of 4.35 mT per unit current, (ii) a 50 Ω transmission circuit with a broad excitation bandwidth of ∼20 MHz, and (iii) an optimized thermal management leading to minimal heating at the sample location. Using individual 13C nuclear spins in the vicinity of a diamond nitrogen-vacancy center as a test system, we demonstrate Rabi frequencies exceeding 70 kHz and nuclear π/2 rotations within 3.4 μs. The extrapolated values for 1H spins are about 240 kHz and 1 μs, respectively. Beyond enabling fast nuclear spin manipulations, our transmitter system is ideally suited for the incorporation of advanced pulse sequences into micro- and nanoscale NMR detectors operating at a low ( less then 1 T) magnetic field.
Homepage: https://www.selleckchem.com/Wnt.html
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