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Li, Y.

Publications and source records attributed to Li, Y..

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Proton-driven plasma wakefield acceleration in AWAKE

In this paper, we briefly summarize the experiments performed during the first Run of the Advanced Wakefield Experiment, AWAKE, at CERN (European Organization for Nuclear Research). The final goal of AWAKE Run 1 (2013–2018) was to demonstrate that 10–20 MeV electrons can be accelerated to GeV-energies in a plasma wakefield driven by a highly-relativistic self-modulated proton bunch. We describe the experiment, outline the measurement concept and present first results. Lastly, we outline our plans for the future.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Design and construction of the MicroBooNE Cosmic Ray Tagger system

The MicroBooNE detector utilizes a liquid argon time projection chamber (LArTPC) with an 85 t active mass to study neutrino interactions along the Booster Neutrino Beam (BNB) at Fermilab. Additionally, with a deployment location near ground level, the detector records many cosmic muon tracks in each beam-related detector trigger that can be misidentified as signals of interest. To reduce these cosmogenic backgrounds, we have designed and constructed a TPC-external Cosmic Ray Tagger (CRT). This sub-system was developed by the Laboratory for High Energy Physics (LHEP), Albert Einstein center for fundamental physics, University of Bern. The system utilizes plastic scintillation modules to provide precise time and position information for TPC-traversing particles. Successful matching of TPC tracks and CRT data will allow us to reduce cosmogenic background and better characterize the light collection system and LArTPC data using cosmic muons. Here, we describe the design and installation of the MicroBooNE CRT system and provide an overview of a series of tests done to verify the proper operation of the system and its components during installation, commissioning, and physics data-taking.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Equipment Protection System for CBETA

The ultimate goal of CBETA is to be the first high-current multi turn Energy Recovery Linac operating at 40 mA. The power of highest energy beam at this configuration is going to be 6 MW. Hence equipment protection against radiation is an important issue. Through our stages of commissioning we will slowly increase the beam current, starting from 100 pA all the way to 1 mA during the current commissioning phase. The electron beams hitting any in-vacuum component either on purpose (e.g. view screens, beam stops or during commissioning) or due to some component failure will generate a radiation shower which has the potential to damage various parts of the accelerator. In this document, we describe the various scenarios which generate unwanted radiation in our machine and list the damage thresholds of critical components. Then we discuss our diagnostic systems which can detect component failure and the resulting radiation generated. We further list the possible beam modes of the machine which we have designed taking into account the damage thresholds and the sensitivity of the diagnostics. Finally, we document our design of the Equipment Protection System (EPS) and outline protocols of calibration and operation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Comparison of $\nu_\mu$-Ar multiplicity distributions observed by MicroBooNE to GENIE model predictions

We measure a large set of observables in inclusive charged current muon neutrino scattering on argon with the MicroBooNE liquid argon time projection chamber operating at Fermilab. We evaluate three neutrino interaction models based on the widely used GENIE event generator using these observables. The measurement uses a data set consisting of neutrino interactions with a final state muon candidate fully contained within the MicroBooNE detector. These data were collected in 2016 with the Fermilab Booster Neutrino Beam, which has an average neutrino energy of $800~\hbox {MeV}$ , using an exposure corresponding to $ 5.0\times 10^{19}$ protons-on-target. The analysis employs fully automatic event selection and charged particle track reconstruction and uses a data-driven technique to separate neutrino interactions from cosmic ray background events. We find that GENIE models consistently describe the shapes of a large number of kinematic distributions for fixed observed multiplicity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

A Comparison of the Fatigue Life of Shot-Peened 4340M Steel with 100, 200, and 300% Coverage

Shot peening has been widely used for improving the fatigue performance of structural components. The objectives of this study are to increase the fatigue life of 4340M steel by shot peening and to compare performance at three different shot-peening coverages (100, 200, and 300%). The results show that the optimum coverage for 4340M steel is 200% in this experiment. Scanning electron microscopy (SEM) was used to evaluate the microstructural properties and estimate the depth and length of the resulting cracks. A proposed innovative technique, which still needs further verification, was applied to enable SEM to differentiate between the appearances of the three coverages. Residual stresses measured using x-ray diffraction showed that 200% coverage had comparatively the highest residual compressive stresses.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low-carrier density and fragile magnetism in a Kondo lattice system

Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states in the dilute carrier limit. It is thus important to explore the routes to understand such systems. One established pathway is through the Kondo effect in metallic nonmagnetic analogs, in the so called half-filling case of one conduction electron and one 4f electron per site. Here, we demonstrate that Kondo-based semimetals develop out of conduction electrons with a low-carrier density in the presence of an even number of rare-earth sites. We do so by studying the Kondo material Yb 3 Ir 4 Ge 13 along with its closed-4f-shell counterpart, Lu 3 Ir 4 Ge 13 . Through magnetotransport, optical conductivity, and thermodynamic measurements, we establish that the correlated semimetallic state of Yb 3 Ir 4 Ge 13 below its Kondo temperature originates from the Kondo effect of a low-carrier conduction-electron background. In addition, it displays fragile magnetism at very low temperatures, which in turn, can be tuned to a Griffiths-phase-like regime through Lu-for-Yb substitution. These findings are connected with recent theoretical studies in simplified models. Furthermore, our results can pave the way to exploring strong correlation physics in a semimetallic environment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Full suppression of runaway electron generation by the mode penetration of resonant magnetic perturbations during disruptions on J-TEXT

The avoidance and suppression of runaway electron (RE) generation during disruptions is of great importance for the safe operation of tokamaks. Massive gas injection is enacted to suppress the generation of REs, but the poor gas mixing efficiency and extremely high density required to suppress RE generation make the full RE suppression unreliable. The magnetic perturbations provide an alternative RE suppression during disruptions. The use of mode penetration induced by resonant magnetic perturbations (RMPs) to suppress RE generation has been investigated on the J-TEXT tokamak. For a sufficiently long mode penetration duration, robust runaway suppression has been reached during the disruptions. The m/n = 2/1 mode RMP with high amplitude excites large magnetic islands inside the plasma and leads to the large-scale destruction of magnetic surfaces during disruptions, which results in RE loss and runaway-free disruptions. The essential island width required for runaway suppression is estimated to be larger than 0.16 as the minor radius. This value might be slightly underestimated because of the misalignment between the electron cyclotron emission diagnostic and the island O-point. NIMROD simulations are used to investigate the effect of magnetic islands on RE generation during disruption, showing that the large magnetic islands have the ability to enhance RE seed loss during disruptions. RMP can excite large magnetic islands in the target plasma without tearing mode and might be a way to prevent RE generation during disruptions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Revealing Color Forces with Transverse Polarized Electron Scattering

The Spin Asymmetries of the Nucleon Experiment measured two double spin asymmetries using a polarized proton target and polarized electron beam at two beam energies, 4.7 and 5.9 GeV. A large acceptance open-configuration detector package identified scattered electrons at 40° and covered a wide range in Bjorken $\mathcal{x}$ (0.3< $\mathcal{x}$ <0.8). Proportional to an average color Lorentz force, the twist-3 matrix element, $\tilde{d}$$p\atop{2}$, was extracted from the measured asymmetries at Q 2 values ranging from 2.0 to 6.0 GeV 2 . The data display the opposite sign compared to most quark models, including the lattice QCD result, and an unexpected scale dependence. Moreover, when combined with the neutron data in the same Q 2 range the results suggest a flavor independent average color Lorentz force.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the decays Λ c → Σ π π at Belle

We report measurements of the branching fractions of the decays Λ c + → Σ + π - π + , Λ c + → Σ 0 π + π 0 and Λ c + → Σ + π 0 π 0 relative to the reference channel Λ c + → p K - π + . The analysis is based on the full data sample collected at and near the Υ ( 4 S ) resonance by the Belle detector at the KEKB asymmetric-energy e + e - collider, corresponding to an integrated luminosity of 711 fb - 1 . We measure B ( Λ c + → Σ + π - π + ) / B ( Λ c + → p K - π + ) = 0.7 19 ± 0.003 ± 0.02 4 , B ( Λ c + → Σ 0 π + π 0 ) / B ( Λ c + → p K - π + ) = 0. 575 ± 0.005 ± 0.0 36 and B ( Λ c + → Σ + π 0 π 0 ) / B ( Λ c + → p K - π + ) = 0. 247 ± 0.006 ± 0.01 9 . The listed uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗