Book Synopsis A Mulitple Cathode Gun Design for the ERHIC Polarized Electron Source by :
Download or read book A Mulitple Cathode Gun Design for the ERHIC Polarized Electron Source written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The future electron-ion collider eRHIC requires a high average current (≈50 mA), short bunch (≈3 mm), low emittance (≈20 [mu]m) polarized electron source. The maximum average current of a polarized electron source so far is more than 1 mA, but much less than 50 mA, from a GaAs:Cs cathode. One possible approach to overcome the average current limit and to achieve the required 50 mA beam for eRHIC, is to combine beamlets from multiple cathodes to one beam. In this paper, we present the feasibility studies of this technique. The future eRHIC project, next upgrade of RHIC, will be the first electron-heavy ion collider in the world. It requires polarized electron source with a high average current (≈50 mA), short bunch (≈3 mm), emittance of about 20 [mu]m and energy spread of ≈1% at 10 MeV. The state-of-art polarized electron cathode can generate average current of about more than 1 mA, but much less than 50 mA. The current is limited by the low quantum efficiency, space charge and ultra-high vacuum requirement of the polarized cathode. A possible approach to achieve the 50 mA beam is to employ multiple cathodes, such as 20 cathodes, and funnel the multiple bunched beams from cathodes to the same axis. Fig.1 illustrates schematically the concept of combining the multiple beams. We name it as 'Gatling gun' because it bears functional similarity to a Gatling gun. Laser beams strike the cathodes sequentially with revolution frequency of 700 kHz. Each beam bunch is focused by a solenoid and is bent toward the combiner. The combiner with rotating bending field bends all bunches arriving the combiner with a rotational pattern to the same axis. The energy of each bunch is modified by a bunching cavity (112MHz) and a 3rd harmonic cavity (336MHz). The bunch length is compressed ballistically in the drift space and is frozen after energy has been boosted to 10 MeV by the Booster linac. Each beam bunch contains 3.5 nC charge. The space charge is very strong at energy of 200 keV. A long bunch, [sigma] of 250 ps, is adopted to reduce the space charge on cathode. To compress the beam to final length of 3 mm (10 ps) can be achieved by ballistic compression with a 3rd harmonic cavity.
