The minimum achievable emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. This is measurable as the mean longitudinal and transverse energy spreads in the photoemitted electrons.
ASTeC constructed the Transverse Energy Spread Spectrometer (TESS) experimental facility to measure both the transverse and longitudinal electron energy spectra from III–V semiconductor, multi–alkali and metal photocathodes. Our R&D facilities also include in–vacuum quantum efficiency measurement, XPS, STM, plus ex–vacuum optical and STM microscopy for surface metrology.
Photocathode intrinsic emittance is strongly affected by surface roughness, and the development of techniques to manufacture the smoothest photocathode is a priority for the electron source community. We present energy distribution measurements for electrons emitted from polycrystalline and single–crystal (100) copper photocathodes as a function of their measured surface roughness.
Jones, L., Juarez-Lopez, D., Militsyn, B., Noakes, T. and Welsch, C., 2018, June. Transverse Energy Distribution Measurements for Polycrystalline and (100) Copper Photocathodes with Known Levels of Surface Roughness. In 9th Int. Particle Accelerator Conf.(IPAC'18), Vancouver, BC, Canada, April 29-May 4, 2018 (pp. 4438-4441). JACOW Publishing, Geneva, Switzerland.
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