IPAC2015 - List of Authors (Cullinan, F.J.)

Paper	Title	Page
MOPWA011	The Damping of Transverse Coherent Instabilities by Harmonic Cavities	102
	F.J. Cullinan, R. Nagaoka SOLEIL, Gif-sur-Yvette, France G. Skripka, P.F. Tavares MAX-lab, Lund, Sweden
	At nonzero chromaticity, the threshold current due to transverse coupled bunch instabilities in an electron storage ring is defined by intrabunch head-tail motion of higher than zeroth order. Multibunch tracking simulations predict that this threshold can be increased to several times its original value through the introduction of bunch lengthening harmonic cavities. One previously suggested explanation is the narrower spectra of the elongated bunches but reliable estimates for the threshold currents are not obtainable for anything other than rigid beam motion since the usual Sacherer formulism is not directly applicable to beams in a non-harmonic potential. A new scheme has been developed in which the decay time of a higher than zeroth order transverse head-tail mode may be estimated by taking into account the synchrotron tune spread generated by the harmonic cavity potential. This scheme is presented along with the results of numerical simulations performed in order to confirm the analytical predictions and justify the assumptions made. The extension of the scheme to more complex scenarios is also discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA011
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MOPWA012	Study of Optimal MBA Lattice Structures for the SOLEIL Upgrade	106
	R. Nagaoka, P. Brunelle, F.J. Cullinan, X.N. Gavaldà, A. Loulergue, A. Nadji, L.S. Nadolski, M.-A. Tordeux SOLEIL, Gif-sur-Yvette, France
	Within the context of a future upgrade of the SOLEIL ring, a series of lattice studies has been made with the aim of reducing the current 4 nm-rad horizontal emittance ex by more than an order of magnitude, with a dynamic aperture allowing off-axis injection. As in most upgrades, the important constraint imposed is to keep all the existing straight sections and photon source points. A particularity of SOLEIL are the short straight sections in half of the 16 double-bend cells, created in between the dipoles, which limits the number of dipoles in a MBA cell. In the previous studies, a combination of 5- and 4BA was followed, where with the use of longitudinal gradient bends (LGBs), ex ~440 pm-rad was obtained. The present paper reports on studies extended along the same strategy: In particular, the feasibility and the attainable ex are pursued with a combination of 7- and 6BA, by employing dipoles with transverse gradient and LGBs. In addition, the effectiveness of a few known nonlinear optimization methods, such as the resonance driving term cancellation, interleaved sextupoles with proper phases, and genetic algorithm-based numerical searches shall be explored.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA012
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

The Damping of Transverse Coherent Instabilities by Harmonic Cavities

102

F.J. Cullinan, R. Nagaoka
SOLEIL, Gif-sur-Yvette, France
G. Skripka, P.F. Tavares
MAX-lab, Lund, Sweden

At nonzero chromaticity, the threshold current due to transverse coupled bunch instabilities in an electron storage ring is defined by intrabunch head-tail motion of higher than zeroth order. Multibunch tracking simulations predict that this threshold can be increased to several times its original value through the introduction of bunch lengthening harmonic cavities. One previously suggested explanation is the narrower spectra of the elongated bunches but reliable estimates for the threshold currents are not obtainable for anything other than rigid beam motion since the usual Sacherer formulism is not directly applicable to beams in a non-harmonic potential. A new scheme has been developed in which the decay time of a higher than zeroth order transverse head-tail mode may be estimated by taking into account the synchrotron tune spread generated by the harmonic cavity potential. This scheme is presented along with the results of numerical simulations performed in order to confirm the analytical predictions and justify the assumptions made. The extension of the scheme to more complex scenarios is also discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA011

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPWA012

Study of Optimal MBA Lattice Structures for the SOLEIL Upgrade

106

R. Nagaoka, P. Brunelle, F.J. Cullinan, X.N. Gavaldà, A. Loulergue, A. Nadji, L.S. Nadolski, M.-A. Tordeux
SOLEIL, Gif-sur-Yvette, France

Within the context of a future upgrade of the SOLEIL ring, a series of lattice studies has been made with the aim of reducing the current 4 nm-rad horizontal emittance ex by more than an order of magnitude, with a dynamic aperture allowing off-axis injection. As in most upgrades, the important constraint imposed is to keep all the existing straight sections and photon source points. A particularity of SOLEIL are the short straight sections in half of the 16 double-bend cells, created in between the dipoles, which limits the number of dipoles in a MBA cell. In the previous studies, a combination of 5- and 4BA was followed, where with the use of longitudinal gradient bends (LGBs), ex ~440 pm-rad was obtained. The present paper reports on studies extended along the same strategy: In particular, the feasibility and the attainable ex are pursued with a combination of 7- and 6BA, by employing dipoles with transverse gradient and LGBs. In addition, the effectiveness of a few known nonlinear optimization methods, such as the resonance driving term cancellation, interleaved sextupoles with proper phases, and genetic algorithm-based numerical searches shall be explored.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA012

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)