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Equilibrium bunch density distribution with passive harmonic cavities in a storage ring

Fernandes Tavares, Pedro LU ; Andersson, Åke LU ; Rosborg, Anders LU and Breunlin, Jonas LU (2014) In Physical Review Special Topics. Accelerators and Beams 17(6).
Abstract
The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime-such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency... (More)
The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime-such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency spread for the MAX IV 3 GeV ring. The equilibrium longitudinal bunch density distribution was calculated by establishing a self-consistent equation for the bunch form factor, describing the bunch shape. The calculations are fully self-consistent in the sense that not only the amplitude but also the phase of the waves excited by the beam in the harmonic cavity were assumed to be a function of the bunch shape, which allowed us to explore a wide parameter range not restricted to the region close to the conditions for which the first and second derivatives of the total rf voltage are zero at the synchronous phase. Our results indicate that up to a factor 5 increase in rms bunch length is achievable with a purely passive system for the MAX IV 3 GeV ring while keeping a relatively large harmonic cavity detuning, thus limiting the unavoidable Robinson antidamping rate from the fundamental mode of a passively operated harmonic cavity to values below the synchrotron radiation damping rate. The paper is complemented by results of measurements performed in the MAX III storage ring, which showed good agreement with calculations following the fully self-consistent approach. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Review Special Topics. Accelerators and Beams
volume
17
issue
6
publisher
American Physical Society
external identifiers
  • wos:000339092300003
  • scopus:84904015542
ISSN
1098-4402
DOI
10.1103/PhysRevSTAB.17.064401
language
English
LU publication?
yes
id
fcdd1964-b43d-4395-8049-f4144be3995e (old id 4598770)
date added to LUP
2014-09-05 12:36:08
date last changed
2017-08-27 04:36:00
@article{fcdd1964-b43d-4395-8049-f4144be3995e,
  abstract     = {The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime-such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency spread for the MAX IV 3 GeV ring. The equilibrium longitudinal bunch density distribution was calculated by establishing a self-consistent equation for the bunch form factor, describing the bunch shape. The calculations are fully self-consistent in the sense that not only the amplitude but also the phase of the waves excited by the beam in the harmonic cavity were assumed to be a function of the bunch shape, which allowed us to explore a wide parameter range not restricted to the region close to the conditions for which the first and second derivatives of the total rf voltage are zero at the synchronous phase. Our results indicate that up to a factor 5 increase in rms bunch length is achievable with a purely passive system for the MAX IV 3 GeV ring while keeping a relatively large harmonic cavity detuning, thus limiting the unavoidable Robinson antidamping rate from the fundamental mode of a passively operated harmonic cavity to values below the synchrotron radiation damping rate. The paper is complemented by results of measurements performed in the MAX III storage ring, which showed good agreement with calculations following the fully self-consistent approach.},
  articleno    = {064401},
  author       = {Fernandes Tavares, Pedro and Andersson, Åke and Rosborg, Anders and Breunlin, Jonas},
  issn         = {1098-4402},
  language     = {eng},
  number       = {6},
  publisher    = {American Physical Society},
  series       = {Physical Review Special Topics. Accelerators and Beams},
  title        = {Equilibrium bunch density distribution with passive harmonic cavities in a storage ring},
  url          = {http://dx.doi.org/10.1103/PhysRevSTAB.17.064401},
  volume       = {17},
  year         = {2014},
}