BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
We observed, for the first time, the emission of an electron beam from a hydrogenated diamond in the emission mode on a phosphor screen. Our experimental device is based on the following concept: primary electrons of a few keV energy generate a large number of secondary electron-hole pairs in a diamond. The secondary electrons are transmitted to the opposite face of the diamond, which is hydrogenated, and emitted from its negative-electron-affinity (NEA) surface. Under our present conditions, the maximum emission gain of the primary electron is about 40, and the bunch charge is 50pC/0.5mm2. Our achievement led to new understanding of the hydrogenated surface of the diamond. We propose an electron-trapping mechanism near the hydrogenated surface. The probability of electron trapping in our tests is less than 70%. The hydrogenated diamond was demonstrated to be extremely robust. After exposure to air for days, the sample exhibited no observable degradation in emission.
AES, Medford, NY
BNL, Upton, Long Island, New York
Funding: AES is funded under DOE SBIR contract #DE-FG02-06ER84450. BNL work is performed under DOE contract #DE-AC02-98CH10886.
The use of an RF electron gun with a magnetized cathode in place of a DC gun for ILC may reduce the requirements for emittance damping rings. Maintaining adequate lifetime of the necessary cathode material requires vacuum levels in the 10-11 torr range. While vacuum levels around the 10-9 torr range are common in a normal conducting RF gun, the cryogenic pumping of the cavity walls of a superconducting RF (SRF) gun may maintain vacuum in the range needed for GaAs cathode longevity. Advanced Energy Systems, Inc. is collaborating with Brookhaven National Laboratory to investigate the generation of polarized electron beams using a SRF photocathode gun. The team is developing an experiment to study the quantum lifetime of a GaAs cathode in a SRF cavity and investigate long term cavity performance while integrated with a cesiated GaAs cathode*. In addition to the experimental investigation, a design is being developed that is compatible with the production of high aspect ratio polarized electron beams. The mechanical and physics aspects of this design will be discussed.
*J. Kewisch, et. al., Presentation at PAC09.
BNL, Upton, Long Island, New York
AES, Medford, NY
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Gallium arsenide cathodes are used in electron guns for the production of polarized electrons. In order to have a sufficient quantum efficiency lifetime of the cathode the vacuum in the gun must be 10-11 torr or better, so that the cathode is not destroyed by ion back bombardment. All successful polarized guns are DC guns, because such vacuum levels can not be obtained in normal conducting RF guns. A superconductive RF gun may provide a sufficient vacuum level due to cryo-pumping of the cavity walls. We report on the progress of our experiment to test such a gun.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
Funding: The work at Tech-X Corp. is supported by the U. S. Department of Energy under the DE-FG02-06ER84509 SBIR grant.
The Relativistic Heavy Ion Collider (RHIC) contributes fundamental advances to nuclear physics by colliding a wide range of ions. A novel electron cooling section, which is a key component of the proposed luminosity upgrade for RHIC, requires the acceleration of high-charge electron bunches with low emittance and energy spread. A promising candidate for the electron source is the recently developed concept of a high quantum efficiency photoinjector with a diamond amplifier. To assist in the development of such an electron source, we have implemented algorithms within the VORPAL particle-in-cell framework for modeling secondary electron and hole generation, and for charge transport in diamond. The algorithms include elastic, phonon, and impurity scattering processes over a wide range of charge carrier energies. Results from simulations using the implemented capabilities will be presented and discussed.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
Funding: The work at Tech-X Corp. is supported by the US DoE under grant DE-FG02-06ER84509.
A promising new concept of a diamond amplified photocathode for generation of high-current, high-brightness, and low thermal emittance electron beams was recently proposed* and is currently under active development. To better understand the different effects involved in the generation of electron beams from diamond, we have been developing models (within the VORPAL computational framework) to simulate secondary electron generation and charge transport. The currently implemented models include inelastic scattering of electrons and holes for generation of electron-hole pairs, elastic, phonon, and charge impurity scattering. We will present results from 3D VORPAL simulations with these capabilities on charge gain as a function of primary electron energy and applied electric field. Moreover, we consider effects of electron and hole cloud expansion (initiated by primary electrons) and separation in a surface domain of diamond.
*I. Ben-Zvi et al., Secondary emission enhanced photoinjector, C-AD Accel. Phys. Rep. C-A/AP/149, BNL (2004).