Instability studies at the CERN Proton Synchrotron during transition crossing

Migliorati, M.; Aumon, Sandra; Koukovini-Platia, Eirini; Huschauer, Alexander; Métral, E.; Sterbini, Guido; Wang, Ning

doi:10.1103/physrevaccelbeams.21.120101

Cited by 17 publications

(18 citation statements)

References 5 publications

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“…Among several geometries, the elliptic cross section is of particular interest because it can be found in circular machines [11][12][13] as well as in undulators for free electron lasers [14].…”

Section: Introductionmentioning

confidence: 99%

Resistive wall impedance in elliptical multilayer vacuum chambers

Migliorati

Palumbo

Zannini

et al. 2019

Phys. Rev. Accel. Beams

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The resistive wall impedance of a vacuum chamber with elliptic cross section is of particular interest for circular particle accelerators as well as for undulators in free electron lasers. By using the electric field of a point charge and of a small dipole moving at arbitrary speed in an elliptical vacuum chamber, expressed in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls by means of the surface impedance, and evaluate the longitudinal and transverse driving and detuning impedances for any beam velocity. We also extend the definition of the Yokoya form factors, valid in the thick wall regime, at any beam energy, and show that, in the ultra-relativistic limit, they coincide with the ones that are found in literature. The method is also extended to the multilayer vacuum chamber case. Under conditions generally satisfied with particle accelerator beam pipes, the classical transmission line theory can be used to modelling the impedance seen by a bunch in a vacuum chamber with several layers as an equivalent circuit with the same number of load impedances, giving, as result, a surface impedance that can be used in combination with the fields of the elliptic geometry to obtain the resistive wall impedance in an elliptical multilayer vacuum chamber. The results are also compared with a more time consuming 3D electromagnetic code and with solutions for known cases of circular and flat beam pipe.

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Section: Introductionmentioning

confidence: 99%

Resistive wall impedance in elliptical multilayer vacuum chambers

Migliorati

Palumbo

Zannini

et al. 2019

Phys. Rev. Accel. Beams

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“…Collective effects due to self-induced electromagnetic fields in a particle accelerator are generally studied by introducing the concepts of wakefield and coupling impedance [1][2][3], which represent, in time and frequency domain respectively, the response of the environment to a point charge traveling inside the beam vacuum chamber or in any of the accelerator devices. These effects can be very important [4], and in some cases they could compromise the machine performance leading to partial or total beam losses [5]. For low energy accelerators with nonrelativistic beams, a not negligible contribution to the total impedance is given by the so-called space charge effects [6,7], which are generated directly by the charge distribution and indirectly by the image charges on the pipe wall.…”

Section: Introductionmentioning

confidence: 99%

Space charge impedance and electromagnetic fields in elliptical vacuum chambers

Migliorati

Biancacci

Masullo

et al. 2018

Phys. Rev. Accel. Beams

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Starting from the electric fields produced by a point charge and a dipole traveling inside a circular vacuum chamber, in this paper we derive a formalism for a complete set of equations that describe the electromagnetic fields and the longitudinal and transverse coupling impedances arising by the interaction of a beam with a perfectly conducting pipe in the case of elliptic geometry. The expressions, which are valid for any frequency and beam energy, are written in terms of expansions of Mathieu functions, allow to range from a circular geometry to the parallel plates, and show an interesting parallelism with the well-known expressions for a circular pipe. We also obtain that, under the approximation of low frequency, the formalism allows us to derive the Laslett coefficients for parallel plates, circular and elliptic beam pipe.

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“…In the Comments to the article [1], the Author asks why we do not mention a possible role of transverse mode coupling instability (TMCI) as mechanism which could explain the instability observed during transition crossing in the proton synchrotron (PS).…”

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confidence: 99%

“…The idea behind the simple approach [beam break-up (BBU)] was that each PyHEADTAIL simulation, as those reported in Fig. 13 of [1], took about one day, and, with the inclusion of space charge effect, as in Fig. 14 of [1], one week by using Graphics Processing Units (GPU). The simple BBU code takes a few seconds, giving the possibility to test in a completely independent way the impedance model of the PS and quickly investigate the sensitivity of some parameters.…”

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confidence: 99%