Arizona State University, Tempe, USA
Cornell University, Ithaca, New York, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Intrinsic emittance of photocathodes limits the brightness of electrons beams produced from photoemission guns. Recent advancements have shown that an order of magnitude improvement in intrinsic emittance over the commonly used polycrystalline metal and semiconductor cathodes is possible via use of single crystalline ordered surfaces of metals, semiconductors and other exotic materials at cryogenic temperatures as cathodes. However, due to practical design considerations, it is not trivial to test such cathodes in existing electron guns. Here we present the design of a 200kV DC electron gun being developed at the Arizona State University for this purpose.
Cornell University, Ithaca, New York, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A better understanding of the properties of photocathode materials can be achieved by integrating advanced growth and surface science techniques in their synthesis and analysis. This is a main research theme of the Center for Bright Beams, whose goal is increasing the brightness of linear electron accelerators. Alkali antimonides are efficient photocathode materials and have very low intrinsic emittance at cryogenic temperatures.* A limiting factors is the surface roughness and chemical inhomogeneity of the films.** We studied the influence of growth parameters on the morphology and composition of Cs3Sb thin films. The films are codeposited using pure element sources and transferred via UHV suitcase to a STM/XPS analysis chamber, to study in particular the influence of substrate temperature and material. This platform can be expanded to more analysis and growth systems thanks to a specially designed sample holder and suitcase. An example is a new cryogenic instrument for intrinsic emittance measurements.
* L. Cultrera et al., Phys. Rev. ST ’ Acc. Beams 18 (2015) 113401
** G. Gevorkian et al., Phys. Rev. Accel. Beams, 21 (2018) 093401
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Alkali antimonides photocathodes are a popular choice of electron source for high average brightness beams, due to their high quantum efficiency (QE) and low mean transverse energy (MTE). This paper describes the first measurements of their nonlinear photoemission properties under sub-ps laser illumination. These measurements include wavelength-resolved power dependence, pulse length dependence, and temporal response. The transition between linear and nonlinear photoemission is observed through the wavelength-resolved scan, and implications of nonlinear photoemission are discussed.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Operational lifetime of GaAs photocathodes is the primary limit for applications as high current spin polarized electron sources in future nuclear physics facilities, such as Electron Ion Collider. Recently, ultrathin Cs2Te on GaAs has shown a successful negative electron affinity (NEA) activation with an improved lifetime by a factor of 5 *. In this work, we report activation of GaAs with Cs, Sb and oxygen. Four different methods of introducing oxygen during the growth was investigated. Cs-Sb-O activated GaAs has shown up to a factor of 40 and 13 improvement in charge extraction lifetime and dark lifetime, respectively.
* Bae, et al. (2018). Rugged spin-polarized electron sources based on negative electron affinity GaAs photocathode with robust Cs2Te coating. Applied Physics Letters, 112(15), 154101.