U.S. Particle Accelerator School

High Brightness Electron Injectors for Light Sources course

Sponsoring University:

University of California, Santa Cruz


High Brightness Electron Injectors for Light Sources


David H. Dowell and John F. Schmerge, SLAC and Steve Lidia, LBNL

Purpose and Audience
The purpose of this course is to introduce students to the physics of electron sources and the technology of high-brightness injectors for light sources. The course is suitable for students with an undergraduate degree in physics, electrical engineering or a related field. It is also appropriate for practitioners of accelerator physics wishing to increase their understanding of the fundamentals of modern electron injectors.

Undergraduate Classical Mechanics, Electromagnetism and Solid State courses plus basic knowledge of accelerator physics.

Instructional Method
The course consists of morning lectures (3 hrs. per class day) and afternoon sessions (2 hrs. per day) for the one week course. Homework will be assigned and explained during the afternoon sessions.

Course Content
The development of the modern RF photo-injector is one of the principal enabling technologies for 4th generation light sources and other free electron lasers. In this course we present a brief history and motivation for research of electron injectors used in free electron lasers. The basic elements of the electron injector are defined. The physical principle of electron emission for thermionic, photo-electric and field emission cathodes is described in detail. The thermal (cathode) emittance is derived and examples given for the three emission processes. The theory of space charge limited emission and the effects of image charge forces on electron dynamics very close to the cathode surface is presented along with experimental examples. Acceleration from the cathode is described by comparing DC and RF acceleration in conjunction with longitudinal and transverse focusing dynamics, and the unequal partitioning of the longitudinal and transverse emittances or temperatures of the beam. The concept of slice or time-dependent emittance is introduced for bunched beams and the fundamental principle of emittance compensation is presented first for the RF gun and then developed as a more general principle to control emittance growth during RF compression and for beam transport such as ERL beam merger systems. System design and the use of modeling codes will be discussed and demonstrated. A description of diagnostics used to measure the beam properties will also be discussed. The course concludes with a discussion of how these ideas are implemented into current state-of-the-art photocathode and thermionic injectors and presents areas of future research to advance the brightness of electron beams for the next generation of injectors.

Reading Requirements
(to be provided by the USPAS) “Theory and Design of Charged Particle Beams” by Martin Reiser, (1994) John Wiley & Sons, Inc. Additional suggested reference: “Electron Physics of Vacuum and Gaseous Devices” by Miroslav Sedlacek, (1996) John Wiley & Sons, Inc. Instructors will provide additional lecture notes and references.

Credit Requirements
Students will be evaluated based on performance: final exam (60%) and homework (40%).