TMCI and Space Charge

TL;DR

This paper investigates how space charge influences the transverse mode-coupling instability (TMCI) thresholds, revealing that the effect varies with wake type and can either increase or decrease stability depending on the parameters.

Contribution

The study extends understanding of TMCI by analyzing the impact of space charge on instability thresholds for different wake oscillation types.

Findings

Threshold increases with space charge for negative wakes.

Threshold decreases inversely with space charge for oscillating wakes.

Results align with previous theoretical predictions.

Abstract

Transverse mode-coupling instability (TMCI) is known to limit bunch intensity. Since space charge (SC) changes the spectra of the collective modes, it affects the TMCI threshold as well. In agreement with results of M. Blaskiewicz and V. Balbekov, we found that, when the wake is negative or it essentially negative, the instability threshold increases as fast as the space charge tune shift when the latter is large enough. In contrast, for oscillating wakes, when the oscillations are sufficiently pronounced, the threshold dependence on SC is non-monotonic; at sufficiently high SC tune shift the threshold goes inversely proportional to that.