Abstract
Photocathodes are a limiting factor for the next generation of ultrahigh brightness photoinjectors. We studied the behavior of a superconducting Pb cathode in the cryogenic environment of a superconducting rf gun cavity to measure the quantum efficiency, its spatial distribution, and the work function. We will also discuss how the cathode surface contaminants modify the performance of the photocathode as well as the gun cavity and we discuss the possibilities to remove these contaminants.
Highlights
Superconducting radio-frequency (SRF) gun cavities are well suited for the production of a high brightness electron beam with high average current, low beam emittance, and long cathode lifetime [1]
In contrast to normal conducting guns, low rf power losses in the SRF guns allow an operation in a continuous wave (CW) mode at high field gradient on the cathode surface, which allows production of an electron beam with high average current and low beam emittance
The electron beam produced in the SRF gun was characterized in the test stand [17] shown in Fig. 2, which is mounted behind the Horizontal Bi-Cavity Test (HoBiCaT) cryostat
Summary
Superconducting radio-frequency (SRF) gun cavities are well suited for the production of a high brightness electron beam with high average current, low beam emittance, and long cathode lifetime [1]. The implementation of a photocathode with high quantum efficiency (QE) and low contribution to the dark current in a way preserving the quality factor of the SRF cavity prior to the cathode deposition is one of the main challenges of the development of SRF electron guns. A choke filter prevents rf losses downstream the cathode Another option to integrate a photocathode into an SRF gun is to use a superconducting cathode. The use of a lead photocathode had been restricted to witness sample measurements at 300 and 80 K only with no measurement data at 2 K, where the cathode is a superconductor [5]. We report on laser cleaning of the superconducting Pb film in an SRF photoinjector cavity
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