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Your search keyword '"Liu, J. C."' showing total 21 results
Start Over Author "Liu, J. C." Publisher edp sciences
21 results on '"Liu, J. C."'

13. Radiation containment at a 1 MWhigh energy electron accelerator: Status of LCLS-II radiation physics design.

Author

Santana Leitner, M., Blaha, J., Guetg, M. W., Li, Z., Liu, J. C., Mao, S. X., Nicolas, L., Rokni, S. H., Xiao, S., and Ge, L.

Subjects
ELECTRON accelerators, RADIATION, ELECTRON beams, X-rays, PHOTON beams
Abstract

LCLS-II will add a 4 GeV, 1 MHz, SCRF electron accelerator in the first 700 meters of the SLAC 2- mile Linac, as well as adjustable gap polarized undulators in the down-beam electron lines, to produce tunable, fully coherent X-rays in programmable bunch patterns. This facility will work in unison with the existing Linac Coherent Light Source, which uses the legacy copper cavities in the last third of the linac to deliver electrons between 2 and 17 GeV to an undulator line. The upgrade plan includes new beam lines, five stages of state of the art collimation that shall clean the high-power beam well up-beam of the radio-sensitive undulators, and new electron and photon beam dumps. This paper describes the challenges encountered to define efficient measures to protect machine, personnel, public and the environment from the potentially destructive power of the beam, while maximizing the reuse of existing components and infrastructure, and allowing for complex operational modes. [ABSTRACT FROM AUTHOR]

Published
2017
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14. Radiation containment at a 1 MWhigh energy electron accelerator: Status of LCLS-II radiation physics design.

Author

Blaha, J., Guetg, M. W., Li, Z., Liu, J. C., Mao, S. X., Nicolas, L., Rokni, S. H., Xiao, S., Ge, L., and Leitner, M. Santana

Subjects
PHYSIOLOGICAL effects of radiation, RADIATION, ELECTRON accelerators, WIGGLER magnets, PHOTON beams
Abstract

LCLS-II will add a 4 GeV, 1 MHz, SCRF electron accelerator in the first 700 meters of the SLAC 2- mile Linac, as well as adjustable gap polarized undulators in the down-beam electron lines, to produce tunable, fully coherent X-rays in programmable bunch patterns. This facility will work in unison with the existing Linac Coherent Light Source, which uses the legacy copper cavities in the last third of the linac to deliver electrons between 2 and 17 GeV to an undulator line. The upgrade plan includes new beam lines, five stages of state of the art collimation that shall clean the high-power beam well up-beam of the radio-sensitive undulators, and new electron and photon beam dumps. This paper describes the challenges encountered to define efficient measures to protect machine, personnel, public and the environment from the potentially destructive power of the beam, while maximizing the reuse of existing components and infrastructure, and allowing for complex operational modes. [ABSTRACT FROM AUTHOR]

Published
2017
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15. Possible systematics in the VLBI catalogs as seen from Gaia.

Author

Liu, N., Zhu, Z., and Liu, J.-C.

Subjects
VERY long baseline interferometry, QUASARS, ASTRONOMICAL catalogs, DEFORMATIONS (Mechanics)
Abstract

Aims. In order to investigate the systematic errors in the very long baseline interferometry (VLBI) positions of extragalactic sources (quasars) and the global differences between Gaia and VLBI catalogs, we use the first data release of Gaia (Gaia DR1) quasar positions as the reference and study the positional offsets of the second realization of the International Celestial Reference Frame (ICRF2) and the Goddard VLBI solution 2016a (gsf2016a) catalogs. Methods. We select a sample of 1032 common sources among three catalogs and adopt two methods to represent the systematics: considering the differential orientation (offset) and declination bias; analyzing with the vector spherical harmonics (VSH) functions. Results. Between two VLBI catalogs and Gaia DR1, we find that: i) the estimated orientation is consistent with the alignment accuracy of Gaia DR1 to ICRF, of ~0.1 mas, but the southern and northern hemispheres show opposite orientations; ii) the declination bias in the southern hemisphere between Gaia DR1 and ICRF2 is estimated to be +152 μas, much larger than that between Gaia DR1 and gsf2016a which is +34 μas. Between two VLBI catalogs, we find that: i) the rotation component shows that ICRF2 and gsf2016a are generally consistent within 30 μas; ii) the glide component and quadrupole component report two declination-dependent offsets: dipolar deformation of ~+50 μas along the Z-axis, and quadrupolar deformation of ~-50 μas that would induce a pattern of sin2δ. Conclusions. The significant declination bias between Gaia DR1 and ICRF2 catalogs reported in previous studies is possibly attributed to the systematic errors of ICRF2 in the southern hemisphere. The global differences between ICRF2 and gsf2016a catalogs imply that possible, mainly declination-dependent systematics exit in the VLBI positions and need further investigations in the future Gaia data release and the next generation of ICRF. [ABSTRACT FROM AUTHOR]

Published
2018
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16. Astrophysical SE2 factor of the 12C(α, γ)16O reaction through the 12C(11B, 7Li)16O transfer reaction.

Author

Guo, B., Du, X. C., Li, Z. H., Li, Y. J., Pang, D. Y., Su, J., Yan, S. Q., Fan, Q. W., Gan, L., Han, Z. Y., Li, E. T., Li, X. Y., Lian, G., Liu, J. C., Pei, C. J., Qiao, L. H., Shen, Y. P., Su, Y., Wang, Y. B., and Zeng, S.

Subjects
CARBON isotopes, OXYGEN isotopes, ANGULAR distribution (Nuclear physics), POTENTIAL barrier, MAGNETIC spectrometer, NUCLEAR astrophysics, TANDEM accelerators
Abstract

The 12C(α, γ)16O reaction plays a key role in the evolution of stars with masses of M > 0.55 M⊙. At the Gamow peak (Ec.m. = 300 keV, T9 = 0.2), the cross section of the 12C(α, γ)16O reaction is so small (about 10-17 barn) that the direct measurement in ground laboratory is not feasible with the existing technology. Up to now, the cross sections at lower energies can only be extrapolated from the data at higher energies. However, two subthreshold resonances, locating at Ex = 7.117 MeV and Ex = 6.917 MeV, make this extrapolation more complicated. In this work the 6.917 MeV subthreshold resonance in the 12C(α, γ)16O reaction was investigated via the 12C(11B,7Li)16O reaction. The experiment was performed using the Q3D magnetic spectrograph at HI-13 tandem accelerator. We measured the angular distribution of the 12C(11B,7Li)16O transfer reaction leading to the 6.917 MeV state. Based on DWBA analysis, we derived the square of ANC of the 6.917 MeV level in 16O to be (2.45 ± 0.28) x1010 fm-1, with which the reduced-α width can be computed. Finally, we calculated the astrophysical SE2 factor of the 6.917 MeV resonance to be 67.6 ± 7.7 keV b. [ABSTRACT FROM AUTHOR]

Published
2016
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