Engineering topics
Publications and source records attributed to Li, Y..
The NSLS-II accelerators finished commissioning in the fall of 2014, with beamline commissioning underway. Part of the design for the NSLS-II is to operate in top off mode. The Top Off Safety System (TOSS) is presently being installed. In this report we discuss the Top Off Safety System design and implementation, along with the necessary tracking results and radiological calculations.
The NSLS-II storage ring (SR) phase I commissioning has been successfully completed in May 12, 2014. In accordance to the project milestone, 25 mA average current was achieved in the storage ring with PETRA III 500 MHz 7-cell PETRA-III RF cavity but w/o ID’s and Landau cavities. In about 5 weeks we delivered a 3 GeV beam to the ring injection straight section, made the 1st turn around the ring, achieved hundreds of turns optimizing injection, stored beam having sextupoles and RF turned ON. Injection efficiency was achieved 95%, close orbit rms value is ~100 um, tune and chromaticity were measured and adjusted as desired, and beam lifetime was a few hours depending on the stored beam current. This report consists of a summary, a chronological part, the injector system performance in Ch3, SR commissioning experience in Ch4 and the outlook of remaining work in Ch5. The SR commissioning experience includes the software experience, hardware (timing, diagnostics, RF, vacuum, PS) operation experience, the strategy for initial injection beam to the stored beam, measurement of the linear optics and control to the desired value, nonlinear beam dynamics study, beam instability study, the subsystem reliability and fault study at different scenarios.
We report the measurement of the direct CP asymmetry in the radiative B¯?Xs+d? decay using a data sample of (772±11)×106 BB¯ pairs collected at the ?(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The CP asymmetry is measured as a function of the photon energy threshold. For E*?=2.1 GeV, where E*? is the photon energy in the center-of-mass frame, we obtain ACP(B¯?Xs+d?)=(2.2±3.9±0.9)%, consistent with the Standard Model prediction.
We report a search for the rare charmless decay B+ → K¯ *0 K *+ using a data sample of 772 × 10 6 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. Here, no statistically significant signal is found and a 90% confidence-level upper limit is set on the decay branching fraction of B(B + → K¯K *0 K *+ ) < 1.31 × 10 –6 .
Here, we report results on studies of the e + e - annihilation into three-body Υ ( n S ) π + π - ( n = 1 , 2 , 3 ) final states including measurements of cross sections and the full amplitude analysis. The cross sections measured at s = 10.866 GeV and corrected for the initial state radiation are σ ( e + e - → Υ ( 1 S ) π + π - ) = ( 2.27 ± 0.12 ± 0.14 ) pb , σ ( e + e - → Υ ( 2 S ) π + π - ) = ( 4.07 ± 0.16 ± 0.45 ) pb , and σ ( e + e - → Υ ( 3 S ) π + π - ) = ( 1.46 ± 0.09 ± 0.16 ) pb . Amplitude analysis of the three-body Υ ( n S ) π + π - final states strongly favors I G ( J P ) = 1 + ( 1 + ) quantum-number assignments for the two bottomonium-like Z b ± states, recently observed in the Υ ( n S ) π ± and h b ( m P ) π ± ( m = 1 , 2 ) decay channels. The results are obtained with a 121.4 fb - 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e - collider.
Verifying the structural integrity of passive components in light water and advanced reactors will be necessary to ensure safe, long-term operations of the existing U.S. nuclear fleet. This objective can be achieved through nondestructive condition monitoring techniques, which can be integrated with plant operations to quantify the “state of health” of structural materials in real-time. While nondestructive methods for monitoring many classes of degradation (such as fatigue or stress corrosion cracking) are relatively advanced, this is not the case for degradation caused by irradiation. The development of nondestructive evaluation technologies for these types of degradation will require advanced materials characterization techniques and tools that enable comprehensive understanding of nuclear reactor material microstructural and behavioral changes under extreme operating environments. Irradiation-induced degradation of reactor steels causes changes in their microstructure that impacts their micro-magnetic properties. In this paper, we describe preliminary results of integrating advanced material characterization techniques with meso-scale computational models. In the future, this will help to provide an interpretive understanding of the state of degradation in structural materials. Microstructural data are presented from monocrystalline Fe and are correlated with variable-field magnetic force microscopy and micro-magnetic measurements. Ongoing research is focused on extending the measurements and models on thin films to gain insights into the structural state of irradiated materials and the resulting impact on magnetic properties. Preliminary conclusions from these correlations are presented, and next steps described.
We present a search for the rare leptonic decays B + → e + ν e and B + → μ + ν μ , using the full Υ(4S) data sample of 772 × 10 6 BB¯ pairs collected with the Belle detector at the KEKB asymmetric-energy e + e – collider. One of the B mesons from the Υ(4S) → BB¯ decay is fully reconstructed in a hadronic mode, while the recoiling side is analyzed for the signal decay. Here, we find no evidence of a signal in any of the decay modes. Upper limits of the corresponding branching fractions are determined as B(B + → e + ν e ) < 3.5 × 10 –6 and B(B + → μ + ν μ ) < 2.7 × 10 –6 at 90% confidence level.
We use ultradeep SCUBA-2 850 μm observations (∼0.37 mJy rms) of the 2 Ms Chandra Deep Field-North (CDF-N) and 4 Ms Chandra Deep Field-South X-ray fields to examine the amount of dusty star formation taking place in the host galaxies of high-redshift X-ray active galactic nuclei (AGNs). Supplementing with COSMOS, we measure the submillimeter fluxes of the 4–8 keV sources at z>1, finding little flux at the highest X-ray luminosities but significant flux at intermediate luminosities. We determine graybody and MIR luminosities by fitting spectral energy distributions to each X-ray source and to each radio source in an ultradeep Karl G. Jansky Very Large Array (VLA) 1.4 GHz (11.5 μJy at 5σ) image of the CDF-N. We confirm the far-infrared (FIR)-radio and mid-infrared (MIR)-radio correlations to z = 4 using the non-X-ray detected radio sources. Both correlations are also obeyed by the X-ray less luminous AGNs but not by the X-ray quasars. We interpret the low FIR luminosities relative to the MIR for the X-ray quasars as being due to a lack of star formation, while the MIR stays high due to the AGN contribution. We find that the FIR luminosity distributions are highly skewed and the means are dominated by a small number of high-luminosity galaxies. Thus, stacking or averaging analyses will overestimate the level of star formation taking place in the bulk of the X-ray sample. We conclude that most of the host galaxies of X-ray quasars are not strong star formers, perhaps because their star formation is suppressed by AGN feedback.
We use 772 × 106 BB meson pairs collected at the Yð4SÞ resonance with the Belle detector to measure the branching fraction for B → Xsγ. Our measurement uses a sum-of-exclusives approach in which 38 of the hadronic final states with strangeness equal to þ1, denoted by Xs, are reconstructed. The inclusive branching fraction for MXs < 2.8 GeV=c2, which corresponds to a minimum photon energy of 1.9 GeV, is measured to be BðB¯ → XsγÞ¼ð3.51 0.17 0.33Þ × 10 -4 , where the first uncertainty is statistical and the second is systematic.
We report the first observation of B 0 →X(3872)(K + π – ) and evidence for B + → X(3872)(K 0 π + ). We measure the product of branching fractions for the former to be B(B 0 → X(3872)(K + π – )) × B(X(3872) → J/ψπ + π – ) = (7.9 ± 1.3(stat) ± 0.4(syst)) × 10 –6 and find that B 0 → X(3872)K*(892) 0 does not dominate the B 0 → X(3872)K + π – decay mode. We also measure B(B + → X(3872)(K 0 π + )) × B(X(3872) → J/ψπ + π – ) = (10.6 ± 3.0(stat) ± 0.9(syst)) × 10 –6 . Furthermore, this study is based on the full data sample of 711 fb –1 (772 × 10 6 BB¯ pairs) collected at the Υ(4S) resonance with the Belle detector at the KEKB collider.
Recent measurements using an X-ray Free Electron Laser (XFEL) and an Electron Beam Ion Trap at the Linac Coherent Light Source facility highlighted large discrepancies between the observed and theoretical values for the Fe xvii 3C/3D line intensity ratio. This result raised the question of whether the theoretical oscillator strengths may be significantly in error, due to insufficiencies in the atomic structure calculations. We present time-dependent spectral modeling of this experiment and show that non-equilibrium effects can dramatically reduce the predicted 3C/3D line intensity ratio, compared with that obtained by simply taking the ratio of oscillator strengths. Once these non-equilibrium effects are accounted for, the measured line intensity ratio can be used to determine a revised value for the 3C/3D oscillator strength ratio, giving a range from 3.0 to 3.5. We also provide a framework to narrow this range further, if more precise information about the pulse parameters can be determined. We discuss the implications of the new results for the use of Fe xvii spectral features as astrophysical diagnostics and investigate the importance of time-dependent effects in interpreting XFEL-excited plasmas.
We report a measurement of the B 0 and B + meson decays to the D$^{–}_{s}$K$^{0}_{S}$π + and D$^{–}_{s}$K + K + final states, respectively, using 657 × 10 6 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. Using the D$^{–}_{s}$ → Φπ – , K* (892) 0 K – and K$^{0}_{S}$K – decay modes for the D s reconstruction, we measure the following branching fractions: B(B 0 → $^{–}_{s}$K$^{0}_{S}$π + ) = [0.47± 0.06(stat) ± 0.05(syst)] × 10 –4 and B(B + → $^{–}_{s}$K + K + ) = [0.93 ± 0.22(stat) ± 0.10(syst)] × 10 –5 . We find the ratio of the branching fraction of B + → $^{–}_{s}$K + K + to that of the analogous Cabibbo-favored B + →$^{–}_{s}$K + π + decay to be R B = 0.054 ± 0.013(stat) ± 0.006(syst), which is consistent with the naive factorization model. We also observe a deviation of the D s K invariant-mass distribution from the three-body phase-space model for both studied decays.
The degradation and breakdown mechanisms of a SiOCH low-k material with k = 2.3 (25% porosity) and thicknesses ranging from 90 nm to 20 nm were investigated. By combining the time dependent dielectric breakdown data at positive/negative bias stress with the thickness scaling results, dielectric failure is proven to be intrinsic and not influenced by copper drift or metal barrier deposition induced dielectric damage. It is shown that stress induced leakage current (SILC) can be used as a measure of dielectric degradation. Therefore, low field lifetimes can be safely estimated using SILC extrapolation. Based on our results, both the impact damage model and the power law model have a good accuracy for low field lifetime prediction. Recovery and anneal experiments are used to study the physical nature causing the observed negative flatband voltage shifts in our metal-insulator-semiconductor planar capacitor structures, where hydrogen induced unstable fast and slow donor type interface states are hypothesized to be the root cause of the observed shifts. We suggest that atomic hydrogen is released from the dielectric during electron injection and migrates to the interfacial region. Our model is further supported by an observed irreversible SILC change during the recovery and anneal studies. The degradation mechanism proposed in this work, supported by the low field lifetime data, provides a feasible explanation for intrinsic low-k dielectric failure.
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