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Title: Initial Performance Measurements of Multi-GHz Electron Bunch Trains

Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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Conference: Presented at: 8th International Particle Accelerator Conference, Copenhagen, Denmark, May 14 - May 19, 2017
Country of Publication:
United States

Citation Formats

Marsh, R A, and Gibson, D J. Initial Performance Measurements of Multi-GHz Electron Bunch Trains. United States: N. p., 2017. Web.
Marsh, R A, & Gibson, D J. Initial Performance Measurements of Multi-GHz Electron Bunch Trains. United States.
Marsh, R A, and Gibson, D J. Thu . "Initial Performance Measurements of Multi-GHz Electron Bunch Trains". United States. doi:.
title = {Initial Performance Measurements of Multi-GHz Electron Bunch Trains},
author = {Marsh, R A and Gibson, D J},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu May 11 00:00:00 EDT 2017},
month = {Thu May 11 00:00:00 EDT 2017}

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  • We demonstrate the generation of a train of electron bunches with variable spacing at the Argonne Wakefield Accelerator. The photocathode ultraviolet laser pulse consists of a train of four pulses produced via polarization splitting using two alpha-BBO crystals. The photoemitted electron bunches are then manipulated in a horizontally-bending dogleg with variable longitudinal dispersion. A downstream vertically-deflecting cavity is then used to diagnose the temporal profile of the electron beam. The generation of a train composed of four bunches with tunable spacing is demonstrated. Such a train of bunch could have application to, e.g., the resonant excitation of wakefield in dielectric-linedmore » structures. We have presented preliminary measurements on a simple technique to generate a train of electron bunches with variable separation. In the initial experiment appreciable density modulation down to wavelengths of {approx}1.8 mm (corresponding to a temporal separation of {approx}6 ps) were achieved for a total charge of 0.5 nC. Finding ways to reach smaller separations is being explored with the help of numerical simulations and will be presented elsewhere.« less
  • By scanning gated cameras and gated tune monitors across the bunch pattern during normal colliding-bunch operation of PEP-II, the tunes and beam sizes of individual bunches were measured simultaneously in the high and low energy storage rings of PEP-II. The measurements were made with 1561 colliding bunches in PEP-II, arranged in trains of 66 bunches, with each bunch in the train separated by 4.2 ns. The tune and beam size measurements were correlated with the current, luminosity, and specific luminosity of the bunch. The results show a vertical tune shift at the start and end of the mini-trains, a luminositymore » droop along the mini-train, and specific luminosity drop in the first and last bunches of the train, since they experience a different parasitic crossing on either side of the interaction point (IP).« less
  • No abstract prepared.
  • Measurement of time-of-arrival or instantaneous longitudinal position is a fundamental beam diagnostic. We present results from a stripline transversal periodic coupler structure which forms the heart of a sub-ps beam timing detector. This filter structure approximates a sinx/x response in the frequency domain which corresponds to a limited pulse length response in the time domain. These techniques have been used extensively in beam feedback systems at 3 GHz center frequencies with operational single-shot resolutions of 200 fs [1]. We present a new design, based on a 11.424 GHz center frequency, which is intended to offer a factor of four improvementmore » in time resolution. Two-dimensional electromagnetic simulation results are shown, and the design optimization approach leading to the final circuit implementation is illustrated. The prototype circuit has been fabricated on 64mil Rogers 4003 and lab frequency domain and time domain data are compared to the 2-D simulation results. Performance of the prototype circuit is shown with applicability to sub-ps beam measurements in LINAC and FEL applications.« less
  • The first of three MW-level 110 GHz was operated into the DIII-D tokamak in late 1996. Two additional units will be commissioned during 1997. Each gyrotron is connected to the Tokamak by a low-loss-windowless evacuated transmission line using circular corrugated waveguide carrying the HE{sub 11} mode. The microwave beam spot is well focused with a spot size of approximately 6 cm and can be steered poloidially from the center to the outer edge of the plasma. The initial operation with about 0.5 MW delivered to a low density plasma for 0.5 s showed good central electron heating with peak temperaturemore » in excess of 10 keV. The system status will be described and the initial physics results will be presented, including heating efficiencies, power deposition profiles, and overall system performance.« less