Speaker
Description
Lead talk of session C-1.
Space Charge: Friend or Foe of Transverse Coherent Stability?
Transverse coherent stability of bunches is a key factor in the performance of high-intensity accelerators. As the brightness frontier is pushed further, space charge plays an increasingly important -- and seemingly contradictory -- role, both modifying and driving collective instabilities as well as providing intrinsic Landau damping.
At the dipole order, space charge can stabilise the centroid through Landau damping of non-rigid head-tail modes [Balbekov 1976] and strongly modify or mitigate transverse mode-coupling instability [Blaskiewicz 1998]. At the same time, strong space charge can destabilise the bunch distribution through spatial amplification of centroid perturbations [Burov 2019 and others].
At second and higher orders, coherent transverse space-charge modes can undergo parametric resonance in periodic focusing systems. The best known example is the second-order envelope instability [Hofmann, Laslett, Smith, and Haber 1982]; analogous coherent resonances occur at higher orders. However, nonlinear space charge forces of realistic beam distributions also generate an incoherent tune spread and hence Landau damping. For Gaussian-like beams, this suppresses instability of third- and higher-order moments [Hofmann, Oeftiger, and Boine-Frankenheim 2021].
This contribution reviews these stabilising and destabilising effects of space charge. Can present and future high-intensity accelerator facilities exploit space-charge-induced Landau damping to intrinsically stabilise bunches when pushing the brightness frontier?