Abstract
In the article of K. Kojima, H. Okamoto, and Y. Tokashiki [Phys. Rev. Accel. Beams 22, 074201 (2019)PRABCJ2469-988810.1103/PhysRevAccelBeams.22.074201] the authors claim that the optimum working point on the tune diagram of circular accelerators at high intensity should be determined by using a framework of coherent resonances instead of the commonly accepted and widely used “standard” diagrams based on incoherent resonance conditions. However, their proposal is based on a questionable interpretation of Vlasov’s equation as well as an over-interpretation of their multi-particle simulations in the case of Gaussian-like distributions. Furthermore, the suggested coherent diagram is not supported by detailed published data from operating synchrotrons at GSI and CERN, which are in line with the incoherent resonance picture. As far as waterbag (or similar truncated) distributions, the authors model of coherent resonance diagrams is not questioned in this Comment.
Highlights
Beams 22, 074201 (2019)] the authors claim that the optimum working point on the tune diagram of circular accelerators at high intensity should be determined by using a framework of coherent resonances instead of the commonly accepted and widely used “standard” diagrams based on incoherent resonance conditions
The suggested coherent diagram is not supported by detailed published data from operating synchrotrons at GSI and CERN, which are in line with the incoherent resonance picture
Resonance diagrams have been used since the early days of circular accelerators
Summary
Technische Universität Darmstadt, Schlossgartenstrasse 8, 64289 Darmstadt, Germany; GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany and Goethe Universität, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany (Received 31 July 2019; accepted 28 January 2020; published 27 February 2020). Beams 22, 074201 (2019)] the authors claim that the optimum working point on the tune diagram of circular accelerators at high intensity should be determined by using a framework of coherent resonances instead of the commonly accepted and widely used “standard” diagrams based on incoherent resonance conditions. It is common to incorporate space charge on a diagram with zero intensity resonance lines by means of a “necktie” including the shift (and spread) of incoherent tunes. Quite a number of authors have considered resonant phenomena going beyond the incoherent picture and investigating a possible role of coherent effects due to space charge. Efforts have been made to demonstrate these second order coherent effects experimentally in circular accelerators, but so far with very limited success. As far as higher than second order coherent (including parametric) resonance effects in circular accelerators the situation is different. The authors claim—already in the abstract—that their coherent resonance condition based on the 1D Vlasov theory in their Ref. [27] (Okamoto and Yokoya), mðν0
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