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MOP019 Transient Thermal Stress Wave Analysis of a Thin Diamond Crystal Under Laser Heat Load ion, laser, FEL, electron 72
  • J. Wu
    SLAC, Menlo Park, California, USA
  • B. Yang
    University of Texas at Arlington, Arlington, USA
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
When a laser pulse impinges on a thin crystal, energy is deposited resulting in an instantaneous temperature surge in the local volume and emission of stress waves. In the present work, we perform a transient thermal stress wave analysis of a diamond layer 200 μm thick in the low energy deposition per pulse regime. The layer thickness and laser spot size are comparable. The analysis reveals the characteristic non-planar stress wave propagation. The stress wave emission lasts by hundreds of nanoseconds, at a time scale relevant to the high-repetition-rate FELs at the megahertz range. The kinetic energy converted from the thermal strain energy is calculated, which may be important to estimate the vibrational amplitude of the thin crystal when excited under repeated heat loads. The transient heat transfer plays an important role in draining the mechanical energy during the dynamic wave emission process.
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WEP015 Current Experimental Work with Diamond Field-Emitter Array Cathodes ion, cathode, experiment, electron 450
  • H.L. Andrews, R.L. Fleming, J.W. Lewellen, K.E. Nichols, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  • B.K. Choi
    Vanderbilt University, Nashville, USA
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
Diamond Field-Emitter Array (DFEA) cathodes are arrays of micron-scale diamond pyramids with nanometer-scale tips, thereby providing high emission currents with small emittance and energy spread. To date they have been demonstrated in a close-diode configuration, spaced only a few hundred microns from a solid anode, and have shown very promising results in terms of emittance, energy spread, and per-tip emission currents. We present recent results investigating DFEA performance in a large-gap configuration, such that the cathodes are a few millimeters from a solid anode, and show that performance is the same or better as the close-diode geometry previously studied. However, array performance is still limited by anode damage. We are redesigning our cathode test stand to overcome the inherent limitations of a solid anode, allow for transport of the emitted beam, and further explore real-world DFEA performance.
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