High-power, high-brightness electron beams are of interest for many applications, especially as drivers for free electron lasers and energy recovery linac light sources. For these particular applications, photoemission injectors are used in most cases, and the initial beam brightness from the injector sets a limit on the quality of the light generated at the end of the accelerator. At Cornell University, we have built such a high-power injector using a DC photoemission gun followed by a superconducting accelerating module. Recent results will be presented demonstrating record setting performance up to 65 mA average current with beam energies of 4-5 MeV. V
Radiationless transition probabilities to the atomic 1s shell are calculated for all transitions that contribute measurably to the Auger effect. Screened nonrelativis tie hydrogenic wave functions areused. The effective charge for the continuum-electron Coulomb wave function is taken to be the geometric mean of the effective charges appropriate for the state fromwhichtheelectron originates and the next-higher state. The results are combined with Scofield's radiative transition probabilities to derive theoretical K-shell Quorescence yields. Agreement with a selected set of most reliable~z measurements is very good in the range from Z=10 to 55, and total K-level widths agree very well with measured values.
Atomic Lf-level Auger and Coster-Kronig widths have been calculated for 14 elements with 33 «Z 85. Nonrelativistic screened hydrogenic wave functions and j-j coupling were used; all pertinent transitions were included that involve final vacancy configurations through fv~zf7~2. With the aid of Scofield's x-ray emission rates, Lf fluorescence yieMs are calculated. Total L f L2 and L3 level widths are compared.
The Cornell University energy recovery linac (ERL) photoinjector has recently demonstrated operation at 20 mA for approximately 8 hours, utilizing a multialkali photocathode deposited on a Si substrate. We describe the recipe for photocathode deposition, and will detail the parameters of the run. Post-run analysis of the photocathode indicates the presence of significant damage to the substrate, perhaps due to ion back-bombardment from the residual beam line gas. While the exact cause of the substrate damage remains unknown, we describe multiple surface characterization techniques (x-ray fluorescence spectroscopy, x-ray diffraction, atomic force, and scanning electron microscopy) used to study the interesting morphological and crystallographic features of the photocathode surface after its use for high current beam production. Finally, we present a simple model of crystal damage due to ion back-bombardment, which agrees qualitatively with the distribution of damage on the substrate surface.
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