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Guo, Weiming

Publications and source records attributed to Guo, Weiming.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Effects of irradiation damage on the hardness and elastic properties of quaternary and high entropy transition metal diborides

Multi-principal component transition metal (TM) diborides represent a class of high-entropy ceramics (HECs) that have received considerable interest in recent years owing to their promising properties for extreme environment applications that include thermal/ environmental barriers, hypersonic vehicles, turbine engines, and next-generation nuclear reactors. While the addition of chemical disorder through the random distribution of TM elements on the cation sublattice has offered opportunities to tailor elastic stiffness and hardness, the effects of irradiation-induced structural damage on the physical properties of these complex materials have remained largely unexplored. To this end, changes in the hardness and elastic moduli of a high-entropy TM diboride (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2 )B 2 and three of its quaternary subsets following irradiation with 10 MeV gold (Au) ions to fluences of up to 6 × 10 15 Au cm -2 are investigated at the micrometer and sub-micrometer length-scales via the dispersion of laser-generated surface acoustic waves (SAW) and nanoindentation, respectively. The nanoindentation measurements show that the TM diborides exhibit an initial increase in hardness following irradiation with energetic Au ions, with a subsequent decrease in hardness following further irradiation. One quaternary composition, (Hf 1/3 Ta 1/3 Ti 1/3 )B 2 , exhibits a notable exception to the trend and continues to exhibit an increase in hardness with ion irradiation fluence. Although differences in the absolute values of the effective elastic moduli obtained from the measured SAW dispersion and nanoindentation are observed (and attributed to microstructural variations at the measurement length-scale), both techniques yield similar trends in the form of an initial reduction and subsequent saturation in the elastic modulus with increasing ion irradiation fluence. The quaternary TM diboride (Hf 1/3 Ta 1/3 Ti 1/3 )B 2 again exhibits a departure from this trend. The high-entropy TM diboride (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2 )B 2 exhibits the greatest recovery in hardness and modulus when irradiated to high ion fluences following initial changes at low fluence, indicating superior resistance to radiation-induced damage over its quaternary counterparts. Opportunities for designing HECs with superior hardness and modulus for enhanced radiation resistance (compared to their single constituent counterparts) by tailoring chemical disorder and bond character in the lattice are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Longitudinal Beam Parameter Tolerances of NSLS-II

Similar to the transverse phase space, the beam parameters in the longitudinal phase space must also be monitored and controlled. In the longitudinal phase space the fundamental parameters are: bunch arrival time(or the corresponding RF phase), average momentum, bunch length, and momentum spread. These parameters are usually perturbed by the various noises in a real machine. The noises could excite longitudinal bunch motion, seen by the users as timing jitter, intensity and wavelength variation, and transverse position shift et al. The longitudinal oscillations also cause longitudinal emittance growth, therefore lengthen the bunch and increase the momentum spread, and eventually decrease the brightness. As a rule of thumb for the tolerances, either transverse or longitudinal, the perturbation caused by the noises should not result in a decrease of brightness by more than 10%. The users are concerned about the longitudinal beam parameters in several ways. First the timing jitter affects the timing-dependent experiments. Even though a photo-diode detection system is usually used to to determine the arrival time, the bandwidth is only about 1 kHz. The users from this category ask for a timing jitter tolerance to be 5% of the RMS bunch length over the frequency range from 500 Hz to 50 kHz. This corresponds to a phase error of Δφ = 1.6 mr or 0.1° for a 10 ps bunch with a 500 MHz rf system.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Longitudinal Beam Parameter Tolerance of NSLS-II

Similar to the transverse phase space, the beam parameters in the longitudinal phase space must also be monitored and controlled. In the longitudinal phase space the fundamental parameters are: bunch arrival time(or the corresponding RF phase), average momentum, bunch length, and momentum spread. These parameters are usually perturbed by the various noises in a real machine. The noises could excite longitudinal bunch motion, seen by the users as timing jitter, intensity and wavelength variation, and transverse position shift et al. The longitudinal oscillations also cause longitudinal emittance growth, therefore lengthen the bunch and increase the momentum spread, and eventually decrease the brightness. As a rule of thumb for the tolerances, either transverse or longitudinal, the perturbation caused by the noises should not result in a decrease of brightness by more than 10%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Reasonable Beam Deviation Envelope for Ray-tracing

At NSLS-II the unused dipole radiation is intercepted by the photon absorbers installed inside the vacuum chamber. The water-cooled absorbers are designed to take away the heat therefore the temperature is kept within the safety limit. However, if the beam orbit is severely perturbed, the radiation fan could pass through the geometry and strikes on the vacuum chamber components. This ray-leakage is a possible reason of the accelerator component temperature rise observed during the high-current operations. The goal of this work is to find the maximum beam deviation at the dipole hence ray-tracing can be re-examined under the operational constraints. The beam is confined to the orbit by the bending and focusing magnets. At NSLS-II the orbit is further controlled by a real time orbit feedback loop. Beam could be lost in any unpredictable direction if the magnet malfunctions. Consequently reasonable assumptions must be made to define the deviation envelope. It was determined that the dipole radiation is not powerful enough to cause damage within 10 ms, for example, if the rf power is shut off and the beam deviates from the orbit. Therefore we consider the radiation produced by the stored beam only; temporarily processes, such as unstable oscillating beam, should not be a concern. The orbit of the stored beam can be altered during magnet failures. The dipole current is interlocked to a small range of ±2% from the nominal value. If the dipole current changes slowly the beam energy automatically adjusts and the orbit remains the same. If the dipole current changes rapidly the beam will not be stable. Therefore dipole variation need not to be considered. For the other magnets we consider one magnet failure at a time because it is unlikely that two fail at the same time. It was found that the beam lifetime drops dramatically if one quadrupole power supply is turned off; therefore this scenario does not meet the stable beam condition. The current of one quadrupole could drop but will not result in orbit change with the feedback on. Beam could survive if one sextupole power supply is turned off, but the orbit will not be changed. Magnet could partially fail, for example, one or part of the coil shorts due to break-down. This is a low probability event and will not be considered. During daily operations the orbit is changed by the correctors and the rf frequency. In this work the correctors and the rf frequency are varied to explore the deviation envelope.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Lattice Schemes for the HEX Beamline at Cell27

This Tech-Note reports the two lattice compensation schemes for incorporating a superconducting wiggle at cell 27 for HEX beamline. Part I discusses a global compensation, and Part II reports a local compensation scheme. Both parts discuss two possible placements for this 1.2m long device, i.e., the center of the device is located at the downstream of the straight center by 1.0m or 1.8m.

36 MATERIALS SCIENCE↗