Beam Instabilities at Strong Space Charge Alexey Burov

Beam Instabilities at Strong Space Charge Alexey Burov Fermilab December 9, 2019 GARD ABP Workshop, LBNL

Space Charge (SC) Is Important for Collective Instabilities SC significantly modifies conditions for beam stability at low and medium energy hadron accelerators. Even at the LHC injection, it changes the transverse instability threshold (TMCI) by about a factor of two. SC effects are important for the Fermilab Booster, CERN PS and SPS, other hadron rings, existing and designed, especially close to transition energy and its crossing. 2

State of the Art. Coasting Beam • Longitudinal Instabilities: all clear, SC is an impedance. • Transverse: SC is not an impedance, but the problem is solved. 3

State of the Art. Bunched Beam, Longitudinal SC is an impedance. Instability: Loss of Landau Damping. Solved. 4

State of the Art. Bunched Beam, Transverse: LD SC is NOT an impedance. Work in progress Landau Damping versus SC parameter 5

State of the Art. Bunched Beam, Transverse: TMCI & SCI dipole moment, SPS 6 H. Bartosik, Ph. D Th. offset, ABS model

State of the Art. Bunched Beam, Transverse: CHI https: //arxiv. org/pdf/1808. 08498. pdf 7 CHI was recently confirmed by Yu. Alexahin

State of the Art. Means of Mitigation 8

Observation vs Theory: CERN PS no fitting at all 9

Observation: Convective Instability at Fermilab Booster at the transition crossing 10

Problems: Theory, Simulations, Measurements Convective instabilities is a recently discovered family of collective effects, which has yet to be studied in many aspects, by all available means. Theoretically and in Simulations, to study • Dependence on chromaticity; • Possibilities of octupoles and e-lenses to mitigate; • Modification by coupled-bunch motion; • Effects of feedbacks; • How it all works at stationary and non–stationary cases. To make measurements wherever possible (Booster, MI, IOTA, PS, SPS, …) for various parameters and compare with models and simulations. 11

The Biggest Problem: People The proclaimed GARD Grand Challenges to increase beam intensities by orders of magnitude are very impressive. However, an opposite scenario is rather going to happen, I think. The expert qualification we have today will be lost tomorrow, unless young people will be trained, and new positions will be opened. This is surely the case for the area of theory and simulations of collective beam dynamics, where the leading experts in the US are 60+, and there are nobody at 40 or younger with comparable skills or even trained by the leaders. When we retire, relatively soon, it’s going to be nobody understanding our papers, nobody able even to run the existing software. The degradation is a real danger. This is the main challenge I see. 12

Thanks for your attention! 13