Diamond Amplified Photocathodes
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1039-P09-02
Diamond Amplified Photocathodes John Smedley1, Ilan Ben-Zvi1, Jen Bohon2, Xiangyun Chang1, Ranjan Grover1, Abdel Isakovic1, Triveni Rao1, and Qiong Wu3 1 Brookhaven National Laboratory, Upton, NY, 11973 2 Case Western Reserve University, Clevand, OH, 44106 3 Indiana University, Bloomington, IN, 47405 ABSTRACT High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogenterminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds. INTRODUCTION Linear electron accelerators have long been capable of producing high average currents (>1A) or low emittance/high brightness (ε ~1µm·rad). Many emerging applications of these accelerators, such as free-electron lasers, linac light sources and ion cooling [1,2] require a high quality beam and a high average current. Direct generation of high currents from photocathodes requires highly efficient cathodes and very powerful lasers. High quantum efficiency (QE) cathodes tend to have short operational lifetimes in accelerator environments, especially when operated at high current. High QE cathodes also tend to use cesium, which has the potential to adversely affect the performance of superconducting photoinjector cavities. In order to alleviate these problems, we are investigating the use of a secondary emitter that will amplify the primary current while acting as a barrier between the primary cathode and the cavity. Synthetic diamond has exhibited secondary electron yield (gain) exceeding 100 [3]. The electrical, mechanical and thermal properties of diamond also make it an ideal candidate for this application. The field of electron transport in and emission from diamond has received considerable work in recent years. Electron emission has been directly measured in a reflection geometry by Yater et al. [4] using hydrogen as well as cesium termination to achieve NEA. This work also measured the energy spectrum of the emitted electrons, showing that the majority of the emitted electrons have energies near the vacuum level, with a FWHM energy spre
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