A new approach to linac resonances and equipartition ?

Abstract

In this note we refer to a recent paper "Equipartition, Reality or Swindle?" presented by Lagniel at HB2012, Beijing, which claims to challenge the currently used approach to describe space charge resonances and emittance exchange with the help of linac-specific stability charts. On the one hand we agree with the general observation that enforcing equipartition (EP)would be an unnecessary constraint; however, we find that the heuristic single-particle arguments and examples presented by Lagniel are speculative and cannot be reconciled with results from self-consistent computer simulation. Thus, we see no justification for Lagniel's suggestions, which include a modified EP definition (treating x and y as correlated). Instead, we suggest to maintain the current approach and to continue using the "conventional" EP definition. With our findings we also respond in some detail to Lagniel's "Topics of Discussion".