Convective instabilities of bunched beams with space charge
- Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
For a single hadron bunch in a circular accelerator at zero chromaticity, without multiturn wakes and without electron clouds and other beams, only one transverse collective instability is possible, the mode-coupling instability (TMCI). For sufficiently strong space charge (SC), the instability threshold of the wake-driven coherent tune shift normally increases linearly with the SC tune shift, as independently concluded by several authors using different methods. This stability condition has, however, a very strange feature: at strong SC, it is totally insensitive to the number of particles. Thus, were it correct, such a beam with sufficiently strong SC, being stable at some intensity, would remain stable at higher intensity, regardless of how much higher. This paper suggests a resolution of this conundrum: while SC suppresses the TMCI, it introduces head-to-tail convective amplifications, which could make the beam even less stable than without SC, even if all the coherent tunes are real, i.e., all the modes are stable in the conventional absolute meaning of the word. This is done using an effective new method of analysis of the beam’s transverse spectrum for arbitrary space charge and wake fields. Two new types of beam instabilities are introduced: the saturating convective instability and the absolute-convective instability.
- Research Organization:
- Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
- Grant/Contract Number:
- AC02-07CH11359
- OSTI ID:
- 1474429
- Alternate ID(s):
- OSTI ID: 1503728
- Report Number(s):
- arXiv:1807.04887; FERMILAB-PUB--18-327-AD-APC; 1682349
- Journal Information:
- Physical Review Accelerators and Beams, Journal Name: Physical Review Accelerators and Beams Journal Issue: 3 Vol. 22; ISSN 2469-9888; ISSN PRABCJ
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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