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Title: Convective instabilities of bunched beams with space charge

Abstract

For a single hadron bunch in a circular accelerator at zero chromaticity, without multiturn wakes and without electron clouds and other beams, only one transverse collective instability is possible, the mode-coupling instability (TMCI). For sufficiently strong space charge (SC), the instability threshold of the wake-driven coherent tune shift normally increases linearly with the SC tune shift, as independently concluded by several authors using different methods. This stability condition has, however, a very strange feature: at strong SC, it is totally insensitive to the number of particles. Thus, were it correct, such a beam with sufficiently strong SC, being stable at some intensity, would remain stable at higher intensity, regardless of how much higher. This paper suggests a resolution of this conundrum: while SC suppresses the TMCI, it introduces head-to-tail convective amplifications, which could make the beam even less stable than without SC, even if all the coherent tunes are real, i.e., all the modes are stable in the conventional absolute meaning of the word. This is done using an effective new method of analysis of the beam’s transverse spectrum for arbitrary space charge and wake fields. Two new types of beam instabilities are introduced: the saturating convective instability and themore » absolute-convective instability.« less

Authors:
 [1]
  1. Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1503728
Alternate Identifier(s):
OSTI ID: 1474429
Report Number(s):
arXiv:1807.04887; FERMILAB-PUB-18-327-AD-APC
Journal ID: ISSN 2469-9888; PRABCJ; 1682349
Grant/Contract Number:  
AC02-07CH11359
Resource Type:
Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Volume: 22; Journal Issue: 3; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Burov, A. Convective instabilities of bunched beams with space charge. United States: N. p., 2019. Web. doi:10.1103/PhysRevAccelBeams.22.034202.
Burov, A. Convective instabilities of bunched beams with space charge. United States. doi:10.1103/PhysRevAccelBeams.22.034202.
Burov, A. Thu . "Convective instabilities of bunched beams with space charge". United States. doi:10.1103/PhysRevAccelBeams.22.034202.
@article{osti_1503728,
title = {Convective instabilities of bunched beams with space charge},
author = {Burov, A.},
abstractNote = {For a single hadron bunch in a circular accelerator at zero chromaticity, without multiturn wakes and without electron clouds and other beams, only one transverse collective instability is possible, the mode-coupling instability (TMCI). For sufficiently strong space charge (SC), the instability threshold of the wake-driven coherent tune shift normally increases linearly with the SC tune shift, as independently concluded by several authors using different methods. This stability condition has, however, a very strange feature: at strong SC, it is totally insensitive to the number of particles. Thus, were it correct, such a beam with sufficiently strong SC, being stable at some intensity, would remain stable at higher intensity, regardless of how much higher. This paper suggests a resolution of this conundrum: while SC suppresses the TMCI, it introduces head-to-tail convective amplifications, which could make the beam even less stable than without SC, even if all the coherent tunes are real, i.e., all the modes are stable in the conventional absolute meaning of the word. This is done using an effective new method of analysis of the beam’s transverse spectrum for arbitrary space charge and wake fields. Two new types of beam instabilities are introduced: the saturating convective instability and the absolute-convective instability.},
doi = {10.1103/PhysRevAccelBeams.22.034202},
journal = {Physical Review Accelerators and Beams},
number = 3,
volume = 22,
place = {United States},
year = {2019},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1103/PhysRevAccelBeams.22.034202

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