Manufacturing and Packaging of Reliable Bialkali Photocathodes via Sputtering

The Relativistic Heavy Ion Collider (RHIC) at BNL is the nation’s premier quantum chromodynamics (QCD) research facility. Its future upgrade calls for the implementation of electron cooling strategies, where ultra-cold electron beams will be generated by photoinjectors. The photocathode, where the electron beam is produced, is required to deliver a significantly high average current (~50 mA) to meet the upgrade requirement. Bialkali cathodes are capable of delivering this high average current, however, based on their lifetimes, they have to be replaced daily. Hence, there’s a need for commercially-available photocathodes than can be produced reliable and supplied in sufficient quantities.How this problem is being addressed: To address this problem, RMD proposed to develop a reliable manufacturing method for bialkali cathodes and for successful sealing/unsealing them in transportable cartridges. By doing so, these cathodes can be mass produced and stockpiled for their daily use at RHIC. The sealed cathodes can be unsealed at the accelerator and handed off easily to a photoinjector gun to produce the electron beam with the desired emittance and brightness.What is to be done in Phase II: The program described in this SBIR seeks to integrate a revolutionary cathode growth method proven for its high volume manufacturing with a reliable cathode sealing technology to provide transportable cathodes for the electron cooler. Specifically, RMD will design and build a cathode growth system, which can reliable produce bialkali cathodes, measure the QE and seal them in a transportable cartridge. Later, these cathodes will be unsealed to re-measure their QE and handed off to a DC gun to produce electron beam and measure its lifetime and current.Commercial Applications and Other Benefits: Key advantage of industrial production and availability of photocathodes is to meet the needs of the burgeoning ultra-fast electron diffraction community. The proposed technology can also disrupt the commercial photocathode manufacturing if QE >40% can be realized, which will boost US’s market share in cathode manufacturing. The technology will enable cost effective photocathode deposition over large areas, which will impact the realization of cost competitive new detectors such as the Large Area Picosecond Photo Detectors (LAPPDs). Availability of such detectors will have a profound impact on medical investigations using PET, tomographic x-ray imaging, border security investigations, scattering neutron detectors for spallation sources to perform basic sciences, deep underground neutrino experiments (DUNE), or the large water neutrino detection systems. The proposed technology could not only streamline the supply of commercial cathodes for accelerators at various national labs but also bring cutting-edge physics into small industries and university labs.