U.S. Particle Accelerator School

Electron Injectors for 4th Generation Light Sources course

Sponsoring University:

University of Texas at Austin


Electron Injectors for 4th Generation Light Sources


Fernando Sannibale, Daniele Filippetto and Christos Papadopoulos, Lawrence Berkeley National Laboratory

Purpose and Audience
With the advent of 4th generation light sources (based on free electron lasers and energy recovery linacs), the need for high-quality electron beams became of utmost importance. The ultimate performance of such light sources relies on the characteristics of the beam from the injector. This course is organized to cover the relevant aspects of this accelerator sub-system, from the requirements to operate in 4th generation light sources, through the physics and dynamics of high brightness beams in the presence of space charge, to the description of the different injector schemes and sub-systems, including the advantages and limitations of the main technologies in use. The course is suitable for entry-level graduate students in physics and engineering or for accelerator scientists and engineers interested in the field of electron injectors.


Students should have had Electromagnetism, Special Relativity, Classical Mechanics and Electrodynamics at the junior level or higher. Some familiarity with accelerator physics is recommended.

It is the responsibility of the student to ensure that he or she meets the course prerequisites or has equivalent experience.

This course is intended to give the student a broad overview of electron injectors with the characteristics for operating in a 4th generation light source. The course will cover both theoretical and experimental aspects as well as technological related issues and limitations. Aspects of analytical and numerical methods used in optimizing and designing high brightness injectors will also be covered. The course material will provide a foundation to design practical injector architectures and to understand the physics of high brightness electron injectors.

Instructional Method
The course will offer a series of lectures during morning sessions, followed by afternoon simulation sessions. During the simulation sessions, the students, organized in small groups, will be introduced to computer simulation codes and techniques and will be gradually guided to design their own electron injector. Each student group will be required to keep a ‘logbook’ during the simulation lab to document the work done. Homework problems will be assigned each day and instructors will be available to help answer questions about the homework and lectures during the evening exercise sessions. There will be a final exam on the last day of class.

Course Content
The course topics include: the role of the electron injector in 4th Generation Light Souces; quality requirements for an electron injector in terms of charge, transverse and longitudinal emittances, brightness, degeneracy parameter, bunch length, peak current, energy, energy spread, repetition rate and reliability; beam dynamics including space charge limit, transverse and longitudinal space charge effects, linear space charge regime (pulse shaping, beam blowout), emittance compensation, low and high gun gradient regimes, bunch compression (‘zero crossing’ buncher, velocity bunching), emittance manipulation (eigen-emittances, flat beams, emittance exchange); simulation tools, popular simulation codes, multi-objective optimization; the cathode system including “thermal” or intrinsic emittance, thermionic cathodes, photo-cathodes, quantum efficiency, laser systems, pulse shaping, metal cathodes, semiconductor cathodes, other cathodes; electron gun technologies including DC Guns, super-conducting RF guns, high frequency RF guns, low frequency RF guns, hybrid guns, DC-SRF, DC-RF; RF systems; injector beam diagnostics.

Reading Requirements
Electronic references will be provided during the course that will serve as the primary reference. Also (to be provided by the USPAS) "The Theory and Design of Charged Particle Beams" Second Edition, Updated and Expanded by Martin Reiser, Wiley & Sons 2008.

Credit Requirements
Students will be evaluated based on performance: homework assignments (60% of final grade), simulation laboratory logbook (15% of final grade), final exam (25% of final grade).

IU/USPAS course: Physics 671