Instructors: Sergey Belomestnykh and Wencan Xu, Brookhaven National Laboratory Oneweek course at USPAS 2011
Purpose and Audience
This
graduate level course covers application of superconducting radio frequency
(SRF) technology to contemporary highbeta accelerators: storage rings, pulsed and
CW linacs, including energy recovery linacs (ERLs). The course will address physics and
engineering aspects of using SRF in accelerators. It will cover beamcavity interactions issues
specific to superconducting cavities, a systems approach to designing SRF
systems and engineering of superconducting cavity cryomodules. The course is intended for graduate students
pursuing accelerator physics and graduate engineers and physicists who want to
familiarize themselves with superconducting RF systems.
Prerequisites: Classical mechanics,
thermodynamics, electrodynamics, and physical or engineering mathematics, all
at entrance graduate level.
Objectives
Upon
completion of this course, the students are expected to understand the physics
underlying RF superconductivity and its application to accelerators, the
advantages and limitations of SRF technology.
The aim is to provide students with ideas and approaches enabling them
to evaluate and solve problems related to application of superconducting
cavities to accelerators, as well actively participate in engineering of SRF
systems for various accelerators.
Instruction Method
This course includes a series of about 20 lectures and exercise
sessions. Homework problems will be assigned which will be graded and answers
provided in the exercise sessions. There will be an openbook, “takehome”
final exam at the conclusion of the course.
Course Content
The
course will include a brief introduction of the basic concepts of microwave
cavities and the basic concepts of RF superconductivity. Then it will cover the beamcavity
interaction issues in accelerators: wake fields and higherorder modes (HOMs)
in superconducting structures, associated with them bunched beam instabilities and
approaches to deal with these instabilities (HOM absorbers and couplers,
polarized cavities, etc.), bunch length manipulation with SRF cavities, beam
loading effects, etc. Following that we
will discuss a systems approach and its application to engineering of SRF
systems for accelerators. Finally, we will address issues related to
engineering of the SRF system components: cryostats, cavities, input couplers,
HOM loads, and frequency tuners.
Reading Requirements
(to be provided by USPAS) “RF Superconductivity
for Accelerators”, by H. Padamsee, J. Knobloch, and T. Hays, John
Wiley & Sons, 2nd edition (2008).
It
is recommended that students refamiliarize themselves with the fundamentals of
electrodynamics at the level of “Fields and Waves in Communication Electronics“
(Chapters 1 through 11) by S. Ramo, J. R. Whinnery, and
T. Van Duzer, John Wiley & Sons, 3rd edition (1994) or
“Classical Electrodynamics” (Chapters 1 through 8) by J. D. Jackson, John
Wiley & Sons, 3rd edition (1999).
Additional suggested reference books (not
provided by USPAS): “Handbook of Accelerator Physics and Engineering”,
edited by A. W. Chao and M. Tigner, World Scientific, 3rd print (2006) “RF Superconductivity: Science, Technology, and Applications,”
by H. Padamsee, WileyVCH (2009). "FundamentalMode RF Design in e+e Storage Ring Factories" by P. B. Wilson, SLACPUB6062 (1993).
Credit Requirements
Students
will be evaluated based on the following performances: final exam (40%), homework
assignments and class participation (30%), Computer Lab project (20%).
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: MathCAD, MATLAB, Microsoft Office.
 Please keep in mind that commercial software (MathCAD, 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 if they do not have it. However, it will be sufficient to use Open Office or Google Docs instead although it may be a bit less convenient.
 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 ProjectThe objective of this project is to compare two different singlecell geometries of superconducting RF cavities for a highcurrent storage ring, such as a thirdgeneration light source, using two computer codes: SUPERFISH and ABCI. The cavity fundamental mode frequency is 500 MHz, the accelerating voltage is 2 MV, the beam pipe diameter is 100 mm, the peak surface electric filed should not exceed 40 MV/m, the peak surface magnetic field should not exceed 100 mT, the Nb cavity is assumed to operate at 4.5 K. Beam parameters: the average current is 500 mA, the rms bunch length is 10 mm, the beam repetition frequency is 50 MHz. Elliptical cavity  Start with the provided sample ABCI input file.
 Run ABCI, make sure you understand how to run the program and review the results. Consult ABCI manual as necessary.
 Make an input file for SUPERFISH. Run SUPERFISH, review the results. Confirm that the fundamental mode frequency if 500 MHz (±1 MHz). Consult SUPERFISH manual as necessary.
 If the beam pipe diameter is not 100 mm, modify the geometry correspondingly, keeping the resonant frequency at 500±1 MHz.
 Calculate the cavity figures of merit, make sure that the peak fields stay within constrains.
 Calculate parameters of at least 5 lowest HOMs.
 Try to optimize the cavity geometry for better performance. Keep the geometry nonreentrant (Why do we want to do this?). Stay within constrains.
 We encourage you to develop a script using you favorite software (MATLAB, MathCAD, Excel,...) for generating new geometries.
 For the optimal geometry create ABCI input file.
 Run ABCI for the rms bunch length of 10 mm. Calculate the HOM loss factor.
Quarter Wave Resonator (QWR)  Start with the provided sample SUPERFISH input file.
 Run SUPERFISH, make sure you understand how to run the program and review the results. Confirm that the fundamental mode frequency if 500 MHz (±1 MHz). Consult SUPERFISH manual as necessary.
 If the beam pipe diameter is not 100 mm, modify the geometry correspondingly, keeping the resonant frequency at 500±1 MHz.
 Calculate the cavity figures of merit, make sure that the peak fields stay within constrains.
 Calculate parameters of at least 5 lowest HOMs.
 Try to optimize the cavity geometry for better performance. Keep the geometry to be QWR (your optimization may try to morph the cavity to become more like a pillbox cavity with a nosecone, so make sure that the length of the cavity coaxial part is close to the quarterwave). Stay within constrains.
 We encourage you to develop a script using you favorite software (MATLAB, MathCAD, Excel,...) for generating new geometries.
 For the optimal geometry create ABCI input file.
 Run ABCI for the rms bunch length of 10 mm. Calculate the HOM loss factor.
Comparison of two geometries Based on the simulation results: i) compare performance of two cavities at fundamental mode (R/Q, Q0, RF power loss, peak fields, …); ii) compare HOM performance of two cavities (frequencies of HOMs, R/Q’s, HOM power, …).
 Write a report summarizing the results of your simulations and comparison of two geometries, make conclusions.
Lecture Notes and Homework Problems
Monday
Tuesday
Questions? Send email to S. Belomestnykh or W. Xu.

