ERL 2009 WG1 Summary Paper Drive Lasers and RF Gun Operation and Challenges

Abstract

Working Group I of the 2009 Energy Recovery Linac Workshop focused on high brightness, high power electron beam sources for energy recovery linacs ERLs , and relevant technology such as development of drive lasers. The WG1 summary paper was broken into two parts DC guns and loadlocks; and RF guns and drive lasers. This was done both to retain more manageable paper sizes, and because SRF guns are in an earlier stage of development than DC guns. This paper describes the advances, concepts, and thoughts for the latter topics presented at the workshop. There are many challenges to the successful operation of SRF guns as high brightness, high average current beam sources. These combine the set of challenges for high current SRF cavities fabrication, cleaning and processing, HOM extraction, etc. , with challenges for high average current photocathode sources photocathode fabrication, quantum efficiency and lifetime, drive laser technology, etc. . New challenges also arise from this combination, such as the requirement for having removable cathodes in an SRF cavity. Practical approaches have been, and are currently being, found to address the problems, and the base of knowledge and experience continues to grow. Alternate ideas are also beginning to make inroads. Hybrid DC SRF guns, pioneered by Peking University, offer promise for combining the best features of both technologies. Quarter wave SRF cavities offer compact size for a given frequency, potentially easier fabrication than elliptical cells, and very high transit time factors for quasi DC operation. Also, the use of normal conducting cavities, usually dismissed out of hand due to the required RF power consumption, may become practical with advanced cavity designs. This paper summarizes the state of the art of drive lasers, cathode development and RF gun based injectors for ERL beam sources The focus in the field has been on DC and SRF guns to date, but interesting approaches for hybrid DC SRF guns and normal conducting RF guns are also presented. The paper concludes with discussions of operational issues and concerns, technical issues related to beam source realization, and future concept