Multipactor in Accelerating Cavities

This book is written by two world-recognized experts in radio frequency (RF) systems for particle accelerators and is based on many years of experience in dealing with the multipactor phenomenon. The authors introduce and review multipactor in RF cavities for scientists and engineers working in the field of accelerator physics and technology. The multipactor phenomenon of unintended electron avalanches occurs in the RF cavities commonly and quite often is a performance-limiting factor. The book starts with an Introductory Overview which contains historical observations and brief description of most common aspects of the phenomenon. Part I deals with the multipactor in a flat gap. It starts with description of the dynamics of electrons, derivation of the stability condition and analyzing influence of several factors on the multipactor. Then, the initial considerations are extended to derive a generalized phase stability and finally a particular case, called ping-pong multipacting, is considered. The part one is concluded with a brief review of computer codes used in multipactor simulations. Part II is dedicated to the multipactor in crossed RF fields, the typical situation in accelerating cavities. Two cases of MP are considered: a two-point multipactor near the cavity equator in elliptical cavities and a one-point multipactor. Part III describes optimization of the cavity shapes geared toward designing multipactor-free structures. The book will serve as an importance reference on multipactor for those involved in developing and operating radio frequency cavities for particle accelerators.

Offers a comprehensive description of multipactor in accelerating cavities for scientists and engineers Provides theoretical treatment of the phenomenon, ties it up with experimental results, and provides insights on developing multipactor-free accelerating cavities Includes historical overview of advances in understanding multipactor

Auteur
Dr. Valery Shemelin received his M.S. degree from Novosibirsk State Technical University and his Ph.D. degree from Budker Institute of Nuclear Physics (Novosibirsk, Russia) where he worked for many years on accelerator projects. Dr. Shemelin joined Cornell University's Laboratory for Elementary Particle Physics in 2000 where he stayed until retirement in 2014. His research interests are concentrated mainly around designing accelerating structures and cavities, optimization of their geometries, studying multipactor discharge, along with simulations and measurements of RF properties of various material at room and cryogenic temperatures. In particular, he made significant contributions to developing superconducting radio frequency cavities and higher order mode absorbers for Energy Recovery Linac (ERL) project at Cornell.
Dr. Sergey Belomestnykh is a Senior Scientist, Chief Technology Officer and Head of Applied Physics and Superconducting Technology Division at Fermi National Accelerator Laboratory (Fermilab). He received his M.S. degree from Novosibirsk State Technical University and his Ph.D. degree from Budker Institute of Nuclear Physics (Novosibirsk, Russia) where he worked for many years and was involved in several accelerator projects developing radio frequency (RF) systems. He joined Cornell University's Laboratory for Elementary Particle Physics in 1994, working on developing superconducting RF (SRF) systems for Cornell Electron Storage Ring (CESR) and Cornell ERL as a CESR RF group leader. In 2010, he joined Brookhaven National Laboratory. In his capacity as a Scientists and Superconducting RF group leader, Dr. Belomestnykh led development of SRF and RF systems for several projects. Since 2015, he is with Fermilab overseeing research and operations of a large Division and coordination technology development throughout the laboratory. He is an Adjunct Professor at the Department of Physics and Astronomy, Stony Brook University. Dr. Belomestnykh is a Fellow of the American Physical Society and a recipient of the 2015 IEEE NPSS Particle Accelerator Science and Technology Award "for achievements in the science and technology of RF and SRF for particle accelerators.

Contenu
Preface.- Introductory Overview.- Part I: Multipactor in a planar gap.- Existence zones for a multipactor discharge.- Introduction.- Distribution of the normal velocity components.- Analysis of the equation of motion.- Stability condition.- Returning electrons.- Energy constraints.- Conclusion.- Generalized phase stability in multipacting.- Introduction.- Distribution of initial velocities and the SEY = 1 boundary.- Stability condition for different points of the multipacting zone.- Other approaches to the phase stability in a flat gap.- Conclusion.- Ping-pong modes.- Introduction.- Boundaries of the ping-pong modes.- Stability boundaries.- Cutoff boundaries.- Lines of equal impact energy.- Boundaries of the two-surface MP and overlapping with the ping-pong MP.- Conclusion.- Simulation of multipactor in a planar gap.- General codes.- Codes ad hoc.- Part II: Multipactor in crossed RF fields.- Effect of the RF cavity magnetic field on multipactor in a gap.- Experimental cavity for 430 MHz.- Inclusion of magnetic field into equations of motion.- Multipactor near the cavity equator.- Introduction.- Fields near equator.- Dependence of the upper arc fields on the lower arc geometry.- Equations of motion.- Condition of stability.- Multipacting maps.- Deviations from the elliptic geometry.- Comparison with experiment.- Conclusion.- Belomestnykh.- One-point multipactor in crossed fields of RF cavities.- Introduction.- Fields and equations of motion in a known geometry with one-point MP.- Comparison of analytical calculations with simulations and experiment.- Influence of change of the surface electric field. Multipactor map.- Phase and space stability. Traveling multipactor.- Comparison of the equations of motion for MP1 and MP2.- Discussion and conclusions.- Part III: Multipacting-free cavities and transitions between cavities and beampipes.- Optimized shape cavities free of MP.- Introduction.- Elliptic geometry and surface fields.- Some definitions.- Method of optimization.- More constraints to the shape of the elliptic cavity.- An example of optimization for the TESLA cavity.- An example of optimization for the SNS elliptic cavity with bgeo = 0.81.- Multipactor consideration.- Conclusion.- Multipacting-free transitions between cavities and beam-pipes. Theorem on minimal electric field.- Introduction.- Cavity with transition from iris to a larger diameter beam-pipe.- Cavity with a tapered end port.- Mechanism of the motion.- Conclusion.