In-Situ Cleaning of Metal Cathodes using a Hydrogen Ion Beam

Dowell, D.H. ; King, F.K. ; Kirby, R.E. ; Schmerge, J.F. ; /SLAC

Stanford Linear Accelerator Center

关键词: Copper;    Data Analysis;    Work Functions;    Cathodes;    Photons;   

DOI  :  10.2172/878343
RP-ID  :  SLAC-PUB-11788
RP-ID  :  AC02-76SF00515
RP-ID  :  878343

美国|英语

来源: UNT Digital Library

【 摘 要 】

Metal photocathodes are commonly used in high-field RF guns because they are robust, straightforward to implement and tolerate relatively poor vacuum compared to semi-conductor cathodes. However these cathodes have low quantum efficiency (QE) even at UV wavelengths, and still require some form of cleaning after installation in the gun. A commonly used process for improving the QE is laser cleaning. In this technique the UV drive laser is focused to a small diameter close to the metal's damage threshold and then moved across the surface to remove contaminants. This method does improve the QE, but can produce non-uniform emission and potentially damage the cathode. Ideally an alternative process which produces an atomically clean, but unaltered surface is needed. In this paper we explore using a hydrogen ion (H-ion) beam to clean a copper cathode. We describe QE measurements over the wavelength range of interest as a function of integrated exposure to an H-ion beam. We also describe the data analysis to obtain the work function and derive a formula of the QE for metal cathodes. Our measured work function for the cleaned sample is in good agreement with published values, and the theoretical QE as a function of photon wavelength is in excellent agreement with the cleaned copper experimental results. Finally, we propose an in-situ installation of an H-ion gun compatible with existing s-band RF guns.