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| TUPPH007 | JAEA Photocathode DC-Gun for an ERL Injector | electron, gun, laser, vacuum | 319 | ||
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ERL light source and FEL require an electron beam of large current and small emittance. In order to realize an electron gun satisfying such requirements, we started developments of a photocathode DC-gun and a new-type NEA-photocathode. The DC-gun consists of a chamber to activate NEA-surface, a 250keV acceleration chamber, and a mode-locked Ti:Sapphire laser. Since extreme high vacuum is essential to obtain a long-life photocathode, we adopt a load-lock system for transporting a photocathode between the chambers, each of which is equipped with an NEG pump. Up to now, we fabricated an electrodes chamber and a high voltage terminal of 250kV and we succeeded in a 250kV high voltage test. We also have suggested a superlattice photocathode as a new-type photocathode with higher performance than an existing technology. Up to now, we fabricated photocathode samples by molecular beam epitaxy and measured quantum efficiency after NEA-surface activation.
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| THPPH063 | In-Situ Cleaning of Metal Photo-Cathodes in RF Guns | gun, cathode, laser, electron | 732 | ||
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Cu cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to "clean" the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and the laser is scanned across the cathode. However, this can also damage the cathode since the laser is operated near the damage threshold and the QE degrades over days and must be cleaned regularly. Alternatively Hydrogen ion beams can be used to clean the cathode and improve the QE but this cleans only the area exposed to the ion beam. In this paper we measure the QE and the dark current emitted from a cathode before and after exposing the gun to a hydrogen plasma created with an rf discharge. With this technique the entire surface of the gun is cleaned simultaneously with no apparent detrimental effects.
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| THPPH069 | Experimental Progress Toward Low Workfunction Controlled Porosity Dispenser Photocathodes | cathode, laser, electron, photon | 748 | ||
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High efficiency, long-lived photocathodes are crucial for continued development of high power FELs. Most photocathodes with high quantum efficiency in the visible range suffer from short lifetime, due to chemical instability of the photosensitive surface layer that evaporates or is contaminated during operation in a RF-injector environment. We propose a controlled porosity dispenser (CPD) concept as a means of rejuvenating photosensitivity and performance. In many high-QE photocathodes, degradation over time is due to the loss of a surface coating of cesium. In CPD cathodes, cesium is replaced at near-room temperature via diffusion, maintaining high QE and extending effective lifetime. Measurements of increasingly complex photoemitting surfaces were performed, yielding QE as a function of cesium coating thickness, temperature, and photon wavelength. These measurements validate a photoemission model* that allows calculation of emission distribution, photocathode performance, and surface conditions of the cathode. Techniques for room-temperature cleaning of the CPD surface were determined and a prototype CPD photocathode based on cesiated sintered tungsten was evaluated.
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* K. L. Jensen, et al., (this conference) |
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