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Lanfa Wang

Bio: Lanfa Wang is an academic researcher from SLAC National Accelerator Laboratory. The author has contributed to research in topics: Storage ring & Beam (structure). The author has an hindex of 8, co-authored 28 publications receiving 178 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, an accelerator-based ultrafast transmission electron microscope (u-TEM) capable of producing a full field image in a single-shot with simultaneous picosecond temporal resolution and nanometer spatial resolution is presented.
Abstract: We present feasibility study of an accelerator-based ultrafast transmission electron microscope (u-TEM) capable of producing a full field image in a single-shot with simultaneous picosecond temporal resolution and nanometer spatial resolution. We study key physics related to performance of u-TEMs and discuss major challenges as well as possible solutions for practical realization of u-TEMs. The feasibility of u-TEMs is confirmed through simulations using realistic electron beam parameters. We anticipate that u-TEMs with a product of temporal and spatial resolution beyond 10 −19 ms will open up new opportunities in probing matter at ultrafast temporal and ultrasmall spatial scales.

36 citations

Journal ArticleDOI
TL;DR: In this article, the authors derived a simple formula for the buildup of ion cloud and instability growth rate with the multibunch train filling pattern, which can significantly reduce the ion density near the beam.
Abstract: The ion-caused beam instability in the future light sources and electron damping rings can be serious due to the high beam current and ultrasmall emittance of picometer level. One simple and effective mitigation of the instability is a multibunch train beam filling pattern which can significantly reduce the ion density near the beam, and therefore reduce the instability growth rate up to 2 orders of magnitude. The suppression is more effective for high intensity beams with low emittance. The distribution and the electric field of trapped ions are benchmarked to validate the model used in the paper. The wakefield of ion cloud and the beam-ion instability is investigated both analytically and numerically. We derived a simple formula for the buildup of ion cloud and instability growth rate with the multibunch train filling pattern. The simulation in NSLSII, PEPX, SuperKEKB, and the observation in SPEAR3 are used to compare with our analyses. The analyses agree well with simulations and observations.

20 citations

Journal ArticleDOI
TL;DR: In this article, the insertion of an isosceles-triangular groove surface and a flat surface were compared and compared, and a large reduction of almost one order of magnitude in measured electron-cloud current was observed when the groove surface was used instead of the flat one.
Abstract: Beam instability caused by an electron cloud is one of the limiting factors in the performance of future advanced positron and proton storage rings. At a wiggler section in the positron ring of the KEK B-factory (KEKB), we installed a test beam chamber with a replaceable insertion and investigated different techniques for the mitigation of electron-cloud effect in a high magnetic field. All techniques were investigated under identical conditions. In this study, the insertions with an isosceles-triangular groove surface and a flat surface were investigated and compared. The groove insertion was composed of grooves running longitudinally along the beam orbit in order to reduce the beam impedance. In this experiment, a large reduction of almost one order of magnitude in the measured electron-cloud current was observed when the groove surface was used instead of the flat one. This is the first experimental demonstration of the concept of the groove surface in a magnetic field. The results are also compared with those obtained in a previous experiment in which a clearing electrode insertion was used.

17 citations

Journal ArticleDOI
TL;DR: In this article, a weak vertical coupled-bunch instability with oscillation amplitude of the order of a few µm was observed in SPEAR3 at nominal vacuum pressure, and the instability becomes stronger with increasing neutral gas pressure as observed by turning off vacuum pumps and becomes weaker when the vertical beam emittance is increased.
Abstract: A weak vertical coupled-bunch instability with oscillation amplitude of the order of a few $\ensuremath{\mu}\mathrm{m}$ has been observed in SPEAR3 at nominal vacuum pressure. The instability becomes stronger with increasing neutral gas pressure as observed by turning off vacuum pumps, and becomes weaker when the vertical beam emittance is increased. These observations indicate that the vertical beam motion is driven by ions trapped in the periodic potential of the electron beam. In this paper we present a series of comprehensive beam measurements, impedance-based stability analysis, and numerical simulations of beam-ion interactions in SPEAR3. The effects of vacuum pressure, gas species, beam current, bunch fill pattern, chromaticity, and vertical beam emittance are investigated.

13 citations

Journal ArticleDOI
TL;DR: In this article, the International Linear Collider (ILC) positron damping ring was modeled for electron cloud buildup and instability in the vacuum chamber of the ILC positron ring, including the effects of diffuse and specular photon scattering.
Abstract: We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications

13 citations


Cited by
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01 Sep 1994
TL;DR: In this article, the authors present a review of Charged Particle Dynamics and Focusing Systems without Space Charge, including Linear Beam Optics with Space Charge and Self-Consistent Theory of Beams.
Abstract: Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

1,311 citations

Journal ArticleDOI
01 Aug 1952-Nature
TL;DR: Lang as discussed by the authors reviewed Lang's work in the Journal of Scientific Instruments (JSI) and Supplement No 1, 1951 Pp xvi + 388 + iii + 80 (London: Institute of Physics, 1951).
Abstract: Journal of Scientific Instruments Editor: Dr H R Lang Vol 28 and Supplement No 1, 1951 Pp xvi + 388 + iii + 80 (London: Institute of Physics, 1951) Bound, £3 12s; unbound, £3

725 citations

ReportDOI
TL;DR: The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV center-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures.
Abstract: The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a "push-pull" configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.

182 citations

01 Jan 2015
TL;DR: In this article, a coded-aperture imaging system for fast neutrons is presented, which consists of a 32-element array of 15 cm, 15 cm � 15 cm -15 cm 15 cm liquid scintillation detectors (EJ-309) mounted behind a 12 -12 pseudorandom coded aperture.
Abstract: This work discusses a large-scale, coded-aperture imager for fast neutrons, building off a proof-of concept instrument developed at the U.S. Naval Research Laboratory (NRL). The Space Science Division at the NRL has a heritage of developing large-scale, mobile systems, using coded-aperture imaging, for long-range γ-ray detection and localization. The fast-neutron, coded-aperture imaging instrument, designed for a mobile unit (20 ft. ISO container), consists of a 32-element array of 15 cm � 15 cm � 15 cm liquid scintillation detectors (EJ-309) mounted behind a 12 � 12 pseudorandom coded aperture. The elements of the aperture are composed of 15 cm � 15 cm � 10 cm blocks of high-density polyethylene (HDPE). The arrangement of the aperture elements produces a shadow pattern on the detector array behind the mask. By measuring of the number of neutron counts per masked and unmasked detector, and with knowledge of the mask pattern, a source image can be deconvolved to obtain a 2-d location. The number of neutrons per detector was obtained by processing the fast signal from each PMT in flash digitizing electronics. Digital pulse shape discrimination (PSD) was performed to filter out the fastneutron signal from the γ background. The prototype instrument was tested at an indoor facility at the NRL with a 1.8-μCi and 13-μCi 252Cf neutron/γ source at three standoff distances of 9, 15 and 26 m (maximum allowed in the facility) over a 15-min integration time. The imaging and detection capabilities of the instrument were tested by moving the source in half- and one-pixel increments across the image plane. We show a representative sample of the results obtained at one-pixel increments for a standoff distance of 9 m. The 1.8-μCi source was not detected at the 26-m standoff. In order to increase the sensitivity of the instrument, we reduced the fastneutron background by shielding the top, sides and back of the detector array with 10-cm-thick HDPE. This shielding configuration led to a reduction in the background by a factor of 1.7 and thus allowed for the detection and localization of the 1.8 μCi. The detection significance for each source at different standoff distances will be discussed. Published by Elsevier B.V.

115 citations