A new approach to linac resonances and equipartition ?

TL;DR

This paper defends the conventional approach to space charge resonances and emittance exchange in linacs, criticizing recent speculative arguments and advocating for continued use of established definitions supported by simulation results.

Contribution

It refutes Lagniel's proposed modifications to equipartition and affirms the validity of the traditional approach based on self-consistent simulations.

Findings

Lagniel's heuristic arguments are speculative and inconsistent with simulations.

The conventional equipartition definition remains valid and justified.

No need to adopt Lagniel's modified equipartition concept.

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".