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Beam-Beam in the ISR (1975)

Beam-Beam in the ISR (1975). Steve Myers.

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Beam-Beam in the ISR (1975)

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  1. Beam-Beam in the ISR (1975) Steve Myers

  2. In the ISR we had to worry about 4 beams: 2 beams per ring. The bunched beam at injection and during acceleration and the debunched already accumulated beam For beams that have significantly different revolution frequencies (caused by different p/p or different charge/mass ratios)Overlap Knock outis an effect where the longitudinal harmonics of the bunch spectrum have components which are equal (“overlap”) to the transverse betatron frequencies and thereby can excite the beam at its transverse resonant frequency (“RF knock-out”) Overlap (n+Q)frev Beam 1 (n-Q)frev hfrev Beam 2 Overlap

  3. Frequency Overlap Conditions (resonance) Harmonic of fbunch Betatron tune of excited beam Region of overlap for test p/p difference between beams

  4. Effect of Two Ring Overlap Knock-out after 360s with injected beam in other ring 3A remain 8A before Top +44mm Top +40mm 0.26A/mm 0.5A/mm

  5. Resonance Conditions and Coupling Mechanism 2 ring machines with particles of different species LHC, RHIC, RF frequencies must always be locked!!

  6. Cures for 2 Beam OLKO • Reduce the higher harmonics of the bunch spectrum by bunch lengthening (lower RF voltage) • Use separations in the interaction regions so that the vector sum of beam beam kicks over one turn is minimized

  7. Effect of Bumps

  8. Dependence on Tune Value

  9. Dependence on Bunch Length

  10. Conclusions • These beam-beam effects in the ISR had a crucial effect on the beam size and hence luminosity • Final Cures • “good” bumps in the IRs • Double decay RF cycle to reduce the higher harmonics of the bunch frequency as quickly as possible

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