Search NASA⌕ Search

Engineering topics

Liu, C.

Publications and source records attributed to Liu, C..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Calculations of anisotropic magnetic properties using spin-orbit energy variations

We analyze several methods of obtaining the accurate relativistic total energy (TE) variations using traditional perturbation theories (PTs) and proposed coupling constant integration (CCI) methods. For this purpose, we perform benchmark calculations within the density functional theory taking the spin-orbit coupling (SOC) and its derivative as a perturbation. The TE change due to SOC addition obtained from both PTs and CCI is shown to reach the accuracy of fully self-consistent TE calculations. Similar accuracy is also obtained even for the magnetocrystalline anisotropy energy (MAE). The real advantage of the proposed methods is to use PTs and CCI methods in those electronic structure methods where accurate total energies currently cannot be obtained with required accuracy. Correspondingly, we demonstrate the applicability of suggested methods for calculations of MAE in different magnetic materials using a dynamic mean-field method. All suggested PTs and CCI methods also provide convenient site, orbital, and spin decompositions of the TE variation, creating a powerful way to analyze microscopic physics in strongly correlated materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Radial Shift Lattice Design using BMAD toolkit

The electron-ion collider (EIC) conceptual design [1] requires that the hadron storage ring (HSR) be able to demonstrate radial shifts using a dual rigidity system. The dual rigidity system is a system in which the dipoles in the utility straight sections(USS) of the EIC lattice have a different rigidity than the arc dipoles thus affecting the beam orbit in the lattice arcs. This difference in rigidity allows the orbital offset in the arc magnets to reach approximately 18.7 mm offset, with a circumference lengthening of 73.2 mm.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Lowering the RHIC-Injection Lambertson Septum magnet to reduce the strength of the RHIC Injection Kickers

The present RHIC beam-injection-system and one of its components the Lambertson septum magnet will be used by the EIC project to inject the hadrons from the AGS into the EIC hadron ring for further acceleration. The number of hadron bunches injected to fill the EIC ring will be almost three times as many as compared to the number of bunches to fill RHIC. The increase of the injected bunches requires new type of kickers known as “transmission line” or “strip line” kickers which provide faster rise time of ~18 nsec, but this type of kickers may not be strong enough to provide the kick required to place the injected beam trajectory into the reference orbit of the circulating beam. In this technical note we provide a modification of the RHIC injection system which consists of lowering the Lambertson septum to decrease the strength of the kickers required to place the injected beam into the reference orbit of the circulating beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films

We report on broadband ferromagnetic resonance linewidth measurements performed on epitaxial Heusler thin films. In this work, a large and anisotropic two-magnon scattering linewidth broadening is observed for measurements with the magnetization lying in the film plane, while linewidth measurements with the magnetization saturated perpendicular to the sample plane reveal low Gilbert damping constants of (1.5 ± 0.1) × 10 –3 , (1.8 ± 0.2) × 10 –3 , and < 8 × 10 –4 for Co 2 MnSi/MgO, Co 2 MnAl/MgO, and Co 2 FeAl/MgO, respectively. The in-plane measurements are fit to a model combining Gilbert and two-magnon scattering contributions to the linewidth, revealing a characteristic disorder length scale of 10–100 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Characterization of a gigabit transceiver for the ATLAS inner tracker pixel detector readout upgrade

We present a gigabit transceiver prototype Application Specific Integrated Circuit (ASIC), GBCR, for the ATLAS Inner Tracker (ITk) Pixel detector readout upgrade. GBCR is designed in a 65-nm CMOS technology and consists of four upstream receiver channels, a downstream transmitter channel, and an Inter-Integrated Circuit (I2C) slave. The upstream channels receive the data at 5.12 Gbps passing through 5-meter 34-American Wire Gauge (AWG) Twin-axial (Twinax) cables, equalize and retime them with a recovered clock, and then drive an optical transmitter. The downstream channel receives the data at 2.56 Gbps from an optical receiver and drives the cable as same as the upstream channels. The jitter of the upstream channel output is measured to be 35 ps (peak-peak) when the Clock-Data Recovery (CDR) module is turned on and the jitter of the downstream channel output after the cable is 138 ps (peak-peak). The power consumption of each upstream channel is 72 mW when the CDR module is turned on and the downstream channel consumes 27 mW. GBCR survives the total ionizing dose of 200 kGy.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Halo removal experiments with hollow electron lens in the BNL Relativistic Heavy Ion Collider

A hollow electron beam has been proposed as an active control tool to remove the beam halo from high-energy, high-current hadron or ion machines (such as the High-Luminosity Large Hadron Collider). To study the halo removal rate and assess the effect on the ion beam core, one of the two electron lenses in the Relativistic Heavy Ion Collider was changed from a Gaussian beam profile to a hollow profile. We describe the design and verification of the hollow electron beam parameters as well as the methods to minimize the hollow beam profile distortions, which can result in an ion beam emittance increase. The hollow beam alignment with the ion beam by using a backscattered electron detector has been demonstrated. Furthermore, experiments were carried out to explore the efficiency of the halo removal by scanning the current and inner radius of the hollow electron beam, which is pulsed either every turn or every nth turn. The effects of the hollow electron beam on the ion beam emittance and luminosity were also assessed experimentally by scanning the inner radius of the electron beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Experimental Demonstration of Hadron Beam Cooling Using Radio-Frequency Accelerated Electron Bunches

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Shear-band cavities and strain hardening in a metallic glass revealed with phase-contrast x-ray tomography

Using high-energy x-ray tomography we show that deformed Zr-based metallic-glass samples contain large amounts of shear-band cavities (internal cracks). Since the investigated samples were unloaded prior to fracture, the three-dimensionally reconstructed samples can be used to determine the true load-bearing area, which leads to the conclusion that the samples have hardened considerably during deformation. We propose how such apparent strain hardening can be caused by a change in friction condition between the detached surfaces instead of searching for an intrinsic hardening mechanism. These results indicate the importance of knowing the true load-bearing area for correct flow-stress determinations of metallic glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Measurement of the Spin Tune Using the Coherent Spin Motion of Polarized Protons in a Storage Ring

This Letter reports the first spin tune measurement at high energies (24 and 255 GeV) with a driven coherent spin motion. To maintain polarization in a polarized proton collider, it is essential to know the spin tune of the polarized proton beam, which is defined as the number of full spin precessions per revolution. A nine-magnet spin flipper has demonstrated high spin-flip efficiency in the presence of two Siberian snakes. The spin flipper drives a spin resonance with a given frequency (or tune) and strength. When the drive tune is close to the spin tune, the proton spin direction is not vertical anymore, but precesses around the vertical direction. By calculating the precession frequency of the horizontal component, the spin tune can be precisely measured. A driven coherent spin motion and fast turn-by-turn polarization measurement are keys to the measurement. The vertical spin direction is restored after turning the spin flipper off and the polarization value is not affected by the measurement. In conclusion, the fact that this manipulation preserves the polarization makes it possible to measure the spin tune during the operation of a high energy accelerator.

43 PARTICLE ACCELERATORS↗