Photocathode Physics

Sponsoring University:

Northern Illinois University

Course:

Photocathode Physics

Instructors:

Jared Maxson, Cornell University; Sid Karkare, Arizona State University
TA: Alimohammed Kachwala, Jefferson Lab

Purpose and Audience
Photocathodes are a ubiquitous choice for electron source in high brightness linear accelerator applications ranging from x-ray free-electron lasers, high-average-current Energy Recovery Linacs, polarized electron sources for future colliders, and more recently for ultrafast time-resolved electron diffraction and microscopy experiments. This course is designed to provide an overview of the physics, fabrication and operation of photocathodes in these accelerator applications. It is appropriate for graduate students in physics/materials-science, and engineering and practicing accelerator physicists and engineers who wish to broaden their knowledge. It is strongly suggested that the students take this course in conjunction with the High Brightness Electron Injectors course offered in the 2nd week of the USPAS session.

Prerequisites
Undergraduate level Classical Mechanics and Electricity and Magnetism are required.  Basic knowledge of Quantum Mechanics and familiarity with programming languages are necessary.  Familiarity with Accelerator Science and Technology at the level of USPAS Fundamentals of Accelerator Physics and Technology with Simulations and Measurements Lab or USPAS graduate Accelerator Physics is recommended.

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

Objectives
This course aims to give the students an understanding of the photoemission process and how various materials and surface properties of cathodes affect the performance of the photoinjector, dictate the demands on the drive lasers, and hence impact the design and performance of different accelerator applications. It will also introduce students to the various cathode materials and their typical performance in accelerators and thereby provide a basic understanding of why one technology may be chosen over the other.

Instructional Method
This course includes a series of lectures in the morning and afternoon sessions. Daily problem sets will be assigned for each session to reinforce materials taught in the lectures. The instructors will be available for guidance during evening homework sessions.

Course Content
This course will provide an overview of the requirements from photocathodes for various accelerator applications and discuss how the various cathode materials fulfil those requirements and perform in photoinjectors. The physics of photoemission and how photoemission properties relevant to accelerators emerge from materials physics and the surface properties of the photocathode will be discussed. The theoretical maximum beam brightness achievable from photocathode sources will be formulated in terms of the material properties of the cathode. We will overview materials, growth processes, and surface characterization techniques that can determine the quality of a photocathode. Various photoemission diagnostics used to measure the accelerator relevant properties of photocathodes will be discussed.

Reading Requirements
Class notes will be provided on a course web site that will serve as the primary reference.  Supplemental text provided by the USPAS: Future of Electron Sources, report of the BES DOE Workshop, 2016 and Advances in Bright Electron Sources, Nuclear Instruments and Methods in Physics Research Section A 907 (2018) 209.

Credit Requirements:
Students will be evaluated based on performance as follows: homework assignments (75% of course grade), class participation (25% of course grade).

USPAS Computer Requirements
There will be no Computer Lab and all participants are required to bring their own portable computer to access online course notes and computer resources. This can be a laptop or a tablet with a sufficiently large screen and keyboard. Windows, Mac, and Linux-based systems that are wifi capable and have a standard web browser and mouse are all acceptable. You should have privileges for software installs. If you are unable to bring a computer, please contact uspas@fnal.gov ASAP to request a laptop loan. Very limited IT support and spare loaner laptops will be available during the session.

Indiana University course number: Physics 671, Advanced Topics in Accelerator Physics
MIT course number: 8.790, Accelerator Physics