Abstract
We present the results of our investigation of lead as a suitable photocathode material for superconducting rf injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and compared to predictions from the three-step model of photoemission. A variety of cathode preparation methods have been used, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Highlights
Several projects being considered require injectors capable of delivering significant average current ( > 1 mA) with near-continuous operation [1,2,3,4]
The output of the monochromator is measured for each wavelength before and after each Quantum efficiencies (QE) measurement, at a point after the lens but prior to the vacuum window, using a power meter (Newport 918-UV)
Lead appears to be an attractive option for moderate average current sources
Summary
Several projects being considered require injectors capable of delivering significant average current ( > 1 mA) with near-continuous operation [1,2,3,4]. Chemical contamination of the superconducting cavity may be a problem for some cathode materials To address this concern, a group at Brookhaven National Laboratory [7] is investigating the use of a diamond capsule to enclose the cathode, with the diamond acting both as an electron multiplier (via secondary emission) and as a barrier to prevent contamination of the cavity by the cathode and contamination of the cathode by the cavity. As the magnetic field on the beam axis is typically small, we do not expect the maximum electric field in the cavity to be impacted by the lead coating This has been verified in recent tests at Jefferson Laboratory [12]. Portions of the experimental section were previously reported [14] in conference proceedings, and are included here for completeness
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