Author: Coleman, J.E.
Paper Title Page
MOPA79 Studying the Emission Characteristics of Field Emission Cathodes with Various Geometries 226
  • M.R. Howard, S.M. Lidia
    FRIB, East Lansing, Michigan, USA
  • J.E. Coleman
    LANL, Los Alamos, New Mexico, USA
  Funding: Work supported by the NNSA of US DOE under contract 89233218CNA000001 and partially supported by the US DOE under Cooperative Agreement award number DE-SC0018362 and Michigan State University.
The cathode test stand (CTS) at LANL is designed to hold off voltages of up to 500kV and can supply pulse durations up to 2.6 μs. Using this test stand, we are able to test both field emission and photocathodes with different geometries and materials at various pulse lengths and PFN voltages. Currently, the test stand is used to evaluate field emission using a velvet cathode over various pulse lengths. The CTS employs various diagnostic tools, including E-dots, B-dots, and a scintillator coupled with a pepperpot mask in order to measure the extracted voltage, current, beam distribution, and transverse emittance. Xenos [1] has been used to create and simulate diode geometries that permits study to optimize various beam parameters. These geometries include changing the size and recess of the cathode as well as implementing a Pierce geometry. Here, we will discuss comparisons for various simulated cathodes and how changes in geometry impact given beam parameters.
[1] See for information about the Xenos software.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA79  
About • Received ※ 02 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022
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TUPA55 Progress Toward Improving Accelerator Performance and Automating Operations with Advanced Analysis Software 465
  • J.E. Koglin, J.E. Coleman, M. McKerns, D. Ronquillo, A. Scheinker
    LANL, Los Alamos, New Mexico, USA
  Funding: Research presented in this conference paper was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project numbers XXG2, XX8R and XXB6.
The penetrating radiography provided by the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility is a key capability in executing a core mission of the Los Alamos National Laboratory (LANL). A new suite of software is being developed in the Python programming language to support operations of the of two DARHT linear induction accelerators (LIAs). Historical data, built as hdf5 data structures for over a decade of operations, are being used to develop automated failure and anomaly detection software and train machine learning models to assist in beam tuning. Adaptive machine learning (AML) that incorporate physics-based models are being designed to use non-invasive diagnostic measurements to address the challenge of time variation in accelerator performance and target density evolution. AML methods are also being developed for experiments that use invasive diagnostics to understand the accelerator behavior at key locations, the results of which will be fed back into the accelerator models. The status and future outlook for these developments will be reported, including how Jupyter notebooks are being used to rapidly deploy these advances as highly-interactive web applications.
poster icon Poster TUPA55 [1.919 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA55  
About • Received ※ 15 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 12 August 2022
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Using Off-Axis Undulator Radiation as a Longitudinal Electron-Beam Diagnostic  
  • Q.R. Marksteiner, H.L. Andrews, J.E. Coleman, W.P. Romero, N.A. Yampolsky, M.R.A. Zuboraj
    LANL, Los Alamos, New Mexico, USA
  • S.K. Barber, R.D. Ryne, J. van Tilborg
    LBNL, Berkeley, California, USA
  • C. Emma
    SLAC, Menlo Park, California, USA
  • B. Ostler
    University of Chicago, Chicago, Illinois, USA
  Funding: This project was supported by funding from the Los Alamos National Laboratory Laboratory Research and Development program.
A novel diagnostic has been developed that uses off-axis undulator radiation to characterize the longitudinal bunch profile of an electron beam. The diagnostic uses a small, ~0.1-m long undulator with mirrors that focus the undulator radiation onto an array of pyrometers. The mirrors both focus the radiation onto the pyrometer and remove the chirping effect that comes from the finite length of the undulator. Numerical and analytical models have been developed to calculate the radiation for a given bunch length, and a phase retrieval algorithm has been developed to extract the bunch profile from measured data. The diagnostic has been installed at the BELLA laser-plasma wakefield accelerator, and will be used to characterize the bunch length there. The concept and relevant results will be presented.
slides icon Slides WEZD4 [3.577 MB]  
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The Challenging Physics Regimes of High Current Electron Beams  
  • J.E. Coleman
    LANL, Los Alamos, New Mexico, USA
  Electrons with intense space charge produce truly challenging physics regimes every step of the way. Hollow electron beams produced in the injector with thin enhanced edges are subject to the diocotron instability or a velocity shear, which is related to the Kelvin Helmholtz instability. Misaligned focusing elements and non-uniform current densities lead to non-linear transport effects in accelerator transport. Electrons focused to intensities >105 J/cm2 or ne ~ 1019 m-3 can produce hot, Te > 1 eV, solid density plasmas that expand slowly over several hundred nanoseconds. The subsequent temperature and density gradients that are produced can generate magnetic fields. Example measurements and calculations of each of these phenomena are presented.  
slides icon Slides THYD2 [7.608 MB]  
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