U.S. Particle Accelerator School
U.S. Particle Accelerator School
Education in Beam Physics and Accelerator Technology

Femtosecond Electron Sources for Ultrafast Sciences

Sponsoring University:

Michigan State University

Course Name:

Femtosecond Electron Sources for Ultrafast Sciences


Chong-Yu Ruan and Phillip M. Duxbury, Michigan State University

Purpose and Audience
The development of ultrafast electron-based diffraction, imaging, and spectroscopy techniques has the potential to revolutionize lab-based diagnostic tools for material characterization and for studying dynamical processes involving different time and length scales. These developments yield capabilities that in many cases are complementary to the ultrafast X-ray approaches; moreover, high quality electron injectors underpin the success of ultrafast x-ray systems such as LCLS and plans for LCLS II.   Remarkably rapid progress in many different forms of electron-based techniques has occurred in recent years, ranging from low energy to mega-eV accelerator-based approaches, which are excelling in different applications. However, critically, independently of the injector designs that separate these different approaches, well designed beam optics, including RF compression and monochromatization technologies for high-density pulses, are required for the generation of high-quality electron beams. The ultimate performance of such electron sources relies on the characteristics of the beam in phase space, namely high-brightness and minimal distortions from the photoelectron injector. This course is organized to cover the design of modern femtosecond electron sources from the perspectives of accelerator physics and beam dynamics; and including ultrafast photophysics at photocathodes. Relevant topics to be covered include the physics and dynamics of high brightness beams in the presence of space charge, to the description of the different electron gun and beam column designs to enable high resolution in time, energy and space. The course is suitable for entry-level graduate students in physics, chemistry, and engineering or for accelerator scientists and engineers interested in the field of small-scale ultrafast electron technologies for ultrafast characterization of fundamental physical, chemical and biological processes; in the gas; solid; plasma and liquid phases.

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

It is the responsibility of the student to ensure that they meet the course prerequisites or have equivalent experience.

This course is intended to give the student a broad overview of electron injectors with the characteristics for designing table-top electron beamlines for ultrafast sciences applications.  The course will cover both theoretical and experimental aspects as well as technology related issues and limitations. Aspects of analytical and numerical methods used in optimizing and designing high brightness injectors for applications such as ultrafast electron diffraction, imaging and spectroscopy will 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 sessions where students will work with simulation and design tools. During the afternoon sessions the students, organized into small groups, will be introduced to computer simulation codes and techniques; and will be gradually guided to design their own electron beam systems. Each student will be required to keep a portfolio of their own work during the laboratory sessions; and during the design project. 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 and discussion sessions. There will be a final 2-hour exam on the last day of class.

Course Content
The course topics include: electron sources and optics for ultrafast electron diffraction, microscopy and spectroscopy; optimization and control of the photocathode properties and beam optics elements for improving the source performance.    Some key topics to be covered include: models of photoemission, phase space, emittance, brightness, nonlinear effects such as aberrations; collective and stochastic space-charge effects, the virtual cathode limit, and emittance compensation.   A range of existing and emerging electron source technologies will be discussed including: thermal and field emitters, DC and AC photoguns, planar and tip photocathode geometries, spin polarized and trapped atom photocathodes.  Beam optics components to be covered include magnetic lenses; RF cavities and energy filters.  Applications to scientific problems in physics, chemistry, biology, medicine; and to industry will be included in the discussions.

Computer Requirements
Students are asked to bring their own laptop computer to class. Please contact the USPAS if you are not able to bring a laptop, we will arrange a loaner for you. The course will use freely available software that is capable of treating strong space charge effects, including WARP (a PIC code) and an N-particle MD solver.  A Fortran code simulating the three step model of photoemission will also be provided.

Reading Requirements
(to be provided by the USPAS) "Theory and Design of Charged Particle Beams" second edition, updated and expanded by Martin Reiser (Wiley 2008). Electronic references will be provided by the instructors..

Credit Requirements
Students will be evaluated based on performance: daily computational exercises during the afternoon sessions (35% of final grade); evening homework assignments (35% of final grade), final exam (30% of final grade).

Michigan State University course number: PHY 905 - 301 - Femtosecond Electron Sources for Ultrafast Sciences
Indiana University course number: Physics 671, Advanced Topics in Accelerator Physics
MIT course number: 8.790, Accelerator Physics