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. Furthermore, the photocathode in the injector, where the electrons are generated, 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. The program described in this SBIR seeks to bring together a proven high volume growth method, with a proven commercial sealing solution to provide cathodes for the electron cooler for RHIC. These cathodes would have the appropriate design to be inserted into the photoinjector, and would have a surface roughness under 1 nm, and thus be able to meet the 5µm emittance specification of the electron cooler. These cathodes, in their self-contained packaging, would be air stable, with a storage lifetime of many years – allowing a sufficient supply for an entire RHIC run to be stockpiled. RMD proposes to develop a low-cost commercial photocathode in a demountable cartridge by meeting the following three objectives: (1) Demonstrate process-reliability for the photocathode sputtering using the proprietary pre-synthesized target, (2) Demonstrate the reproducibility of the sputter-grown cathodes, and (3) Demonstrate the feasibility of sealing and unsealing the cathode from a cartridge without impacting the cathode’s pristine performance. Commercial Applications and Other Benefits: The availability of cathodes in a demountable cartridge 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. The proposed technology has the potential to disrupt the commercial photocathode manufacturing in order to realize large area cathodes with >40% QE in a consistent manner, which will enable manufacturing of such cathodes in the United States. 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 full body scanners for 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.