Transverse mode-coupling instability with Landau cavities at the MAX IV laboratory 1.5 GeV ring

Collective effects can have a strong influence on the beam
stability and performance in synchrotron light sources. Lan-
dau cavities or RF harmonic cavities are a tool that is em-
ployed at 4th generation storage ring light sources to reduce
the impact of or even prevent instabilities arising from collec-
tive effects. The positive effect of Landau cavities is based
on the lengthening of the electron bunches and an increase in
synchrotron tune spread. Recent theoretical calculations by
M. Venturini (2018) predict however, that at zero chromatic-
ity, the threshold current of the transverse mode-coupling
instability (TMCI) was reduced in the presence of Landau
cavities.