# RF Superconductivity for Particle Accelerators

Instructors:

* Sergey Belomestnykh* and

**Alexander Romanenko**Fermi National Accelerator Laboratory

Two-week course at USPAS 2017, Lisle, IL

June 12-23, 2017

## Purpose and Audience

The two-week course will cover the science fundamentals and practical manufacturing, processing, and operational aspects of the superconducting RF cavities – the state-of-the-art technology used for both pulsed and CW particle acceleration. The course is intended to give a comprehensive introduction to the field for students, engineers, and physicists interested in entering this field, as well as to deepen understanding of the technology for those already exposed to some aspects of SRF.

## Prerequisites

Basic knowledge of electromagnetism, microwave techniques, and solid state/condensed matter physics at an undergraduate level.

## Objectives

Upon completion of the course students are expected to have a clear understanding of the advantages, basic underlying physics, open questions, and domain of applicability of SRF technology, as well as state-of-the-art infrastructure and techniques required for successful implementation of SRF-based accelerators.

## Instructional Method

The course will include lectures, computer lab, practical laboratory demonstrations, and instructional lab exercises performed at the extensive Fermilab SRF infrastructure. Homework problems will be assigned during the course, and a final exam at the end of the course will be given.

## Course Content

The course lectures will start from an introduction to the principles of RF acceleration and a general mathematical description of microwave cavities. The phenomenon of superconductivity, and the advantages it brings for RF cavities will then be discussed in detail. In-depth coverage of principles of RF superconductivity and various types of SRF cavities used for different applications will follow. Extrinsic phenomena adversely affecting the performance will be discussed including multipacting, field emission, hydrogen Q-disease. Modern cavity manufacturing, processing, and basic measurement techniques will then be reviewed. Key steps and challenges in engineering and operating of complete SRF cryomodules (cryostats, cavities, input couplers, higher order mode couplers and loads, frequency tuners) will be fully discussed. Beam-cavity interaction issues in operation will also be reviewed. Overview of the recent scientific progress and future outlook with standing challenges and promising research directions will conclude the course. Several practical exercises and demonstration for key topics will be integrated in the course. The practical exercises will utilize world-class SRF facilities at Fermilab.

## Reading Requirements and Suggestions

**The following textbook provided by USPAS will be extensively used during the course:**

**H. Padamsee, J. Knobloch, and T. Hays, RF Superconductivity for Accelerators, John Wiley and Sons, 2^{nd} edition (2008)**

It is recommended that students refresh their knowledge of the fundamentals of electrodynamics at the level of one of the following textbooks:

- S. Ramo, J. R. Whinnery, and T. Van Duzer,
*Fields and Waves in Communication Electronics*(Chapters 1 through 11), John Wiley & Sons, 3rd edition (1994) - J. D. Jackson,
*Classical Electrodynamics*(Chapters 1 through 8), John Wiley & Sons, 3rd edition (1999) - R. E. Collins,
*Foundations for Microwave Engineering*(Chapters 1 through 8), John Wiley & Sons (2001)

and their knowledge of condensed matter physics/superconductivity at the level of:

- N. W. Ashcroft and N. D. Mermin,
*Solid State Physics*(Chapter 34-Superconductivity), Cengage Learning (1976) - M. Tinkham,
*Introduction to superconductivity: second edition*(Chapters 1-2), Dover Books on Physics (2004)

Additional suggested reference books:

*Handbook of Accelerator Physics and Engineering,*edited by A. W. Chao, K. H. Mess, M. Tigner and F. Zimmermann, World Scientific, 2nd Edition (2013)- H. Padamsee,
*RF Superconductivity: Science, Technology, and Applications,*Wiley-VCH (2009).

Reference materials on wakefileds, wake potentials and beam loading:

*"Introduction to Wakefields and Wake Potentials"**by P. B. Wilson, SLAC-PUB-4547 (1989).**"High Energy Electron Linacs: Application to Storage Ring RF Systems and Linear Colliders"**by P. B. Wilson, SLAC-PUB-2884 (1982).**"Fundamental-Mode RF Design in e+e- Storage Ring Factories"**by P. B. Wilson, SLAC-PUB-6062 (1993).*

## Credit Requirements

Students will be evaluated based on the following performances: final exam (40%), homework assignments and class participation (35%) and lab exercises (25%).

## Computer Lab and Codes

During the Computer Lab sessions students will be working on a project using computer codes ABCI and SUPERFISH. The codes will be installed on the USPAS computers. The other codes that will be available on the USPAS computers are: MATLAB, Microsoft Office.

Please keep in mind that commercial software (MATLAB, Microsoft Office) will not be available for installation on students' laptops due to licensing issues. Students will have to use USPAS computers to have access to these software packages if they do not have it. However, it will be sufficient to use LibreOffice or Google Docs instead.

- ABCI code and documentation can be downloaded from the ABCI Home Page. It is available in Windows and Linux versions.
- SUPERFISH can be downloaded from the LANL Accelerator Code Group Download Area for Poisson Superfish. It has only Windows version.

## Computer Lab Project

## Lecture Notes and Homework Problems

**Monday, June 12**

*Lecture 1: Introduction: Advantages and limitations of SRF technology**(S. Belomestnykh)**Lecture 2: Fundamentals of RF and microwave engineering**(S. Belomestnykh)**Lecture 3: Basic concepts of RF superconductivity**(A. Romanenko) - 2-hour lecture**Lecture 4: Related phenomena: Field emission, multipacting, ponderomotive effects**(A. Romanenko)**Lecture 5: Cavity testing techniques**(S. Belomestnykh)*

*Monday 1 homework problems with solutions*

**Tuesday, June 13**

*Lecture 6: SRF systems: Requirements and challenges**(S. Belomestnykh)**Lecture 7: Beam-cavity interaction: Fundamental mode beam loading, wake fields and higher-order modes, instabilities and cures**(S. Belomestnykh)**Computer Lab: Introduction**Lecture 8: Systems engineering approach to SRF system design: interconnectedness, cost optimization**(S. Belomestnykh)**Homework review*

*Derivation of the RF power formula for a beam loaded cavity can be found in RF_power_with_beam_loading.pdf*

*Tuesday 1 homework problems with solutions*

**Wednesday, June 14**

*Lecture 9: Cavity design and optimization**(A. Romanenko)**Lecture 10: Cryomodule design**(S. Belomestnykh)**Computer Lab**Guest lecture: Nitrogen doping and infusion: state-of-the-art and practical aspects**(A. Grassellino)**Lecture 11: Case study: LCLS-II**(A. Romanenko)**Homework review*

*Wednesday 1 homework problems with solutions*

**Thursday, June 15**

*Contemporary 3D computer codes: ANSYS**(S. Cheban)**Contemporary 3D computer codes: COMSOL**(M. Hassan)**Computer Lab**Contemporary 3D computer codes: Microwave Studio**(A. Lunin)**Contemporary 3D computer code demos (S. Cheban, M. Hassan, A. Lunin)**Homework review*

**Friday, June 16**

Hands-on experience day at Fermilab

*RF measurements (M. Hassan and P. Berrutti)**Vertical cavity testing (A. Melnychuk and M. Checchin)*

* Notes for VTS hands-on experience at Fermilab*

*Friday 1 homework problems with solution*

**Monday, June 19**

*Lecture 12: Cavity frequency tuners**(A. Romanenko)**Lecture 13: Fundamental power couplers**(S. Belomestnykh)**Lecture 14: HOM dampers**(S. Belomestnykh)**Computer Lab - 2 hours**Homework review*

**Tuesday, June 20**

*Lecture 15: Cavity fabrication and preparation techniques**(A. Romanenko)**Lecture 16: Cryomodule production cycle**(A. Romanenko)**Lecture 17: High-power RF systems**(S. Belomestnykh)**Computer Lab - 2 hours**Homework review*

*Tuesday 2 homework problems with solution*

**Wednesday, June 21**

Hands-on experience day at Fermilab

*Materials science (Y. Trenikhina and Z. Sung)**Clean room and chemical facilities (D. Bice, A. Rowe and C. Crawford)*

**Thursday, June 22**

*Lecture 18-19 (2 hours): Basic SRF science puzzles**(A. Romanenko)**Final exam intro**Computer Lab**Homework review*

*Take home exam problems with solutions*

**Friday, June 23**

*Final exam Q&A**Lecture 20: Remaining challenges and outlook**(S. Belomestnykh)**Students' feedback, general discussion*