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Exploring Beam-Beam Limits in Electron-Positron Storage Rings: LEP Experience

This presentation discusses the complex topic of beam-beam limits in electron-positron storage rings, focusing on the experiences gathered at CERN's LEP. It outlines several defining limits and introduces an empirical stochastic model that relates the beam-beam parameter to energy and time. The key takeaway is that beam-beam interactions lead to the growth of vertical emittance, which ultimately constrains the achievable beam-beam parameter and overall luminosity. Measurements indicate a maximum vertical beam-beam parameter of 0.083, with achievable values around 0.11 - 0.12 at approximately 100 GeV.

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Exploring Beam-Beam Limits in Electron-Positron Storage Rings: LEP Experience

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Presentation Transcript

  1. LEP Beam-Beam Limit R. Assmann LEP3 Day, 18.6.2012, CERN

  2. Introduction • The beam-beam limit in e+e- storage rings is a difficult subject, studied by many colleagues over the years. No complete overview in 10 min! • Several limits can be defined and exist. • Here: Experience at LEP. • Empirical stochastic model for the achievable beam-beam parameter versus energy and time. • Basically: Beam-beam interaction blows up vertical emittance which in turn limits achievable beam-beam parameter and luminosity.

  3. Reference EPAC 2000

  4. LEP Measurements

  5. Theory I Vertical beam-beam parameter Prediction S. Peggs Damping Decrement

  6. Parametric Model simple stochastic theory of the beam-beam interaction to derive the relationship between the vertical beam-beam parameter and bunch current i A is a machine and optics dependent number times the zero current (unperturbed) vertical emittance(if the horizontal beam-beam blow-up is small).

  7. B gives the inverse asymptotic vertical beam-beam parameter

  8. Unperturbed Vertical Emittance • Means: Vertical emittance unperturbed by beam-beam. • For zero vertical orbit and therefore zero vertical dispersion, it is assumed to approach zero (of course it would then be limited by other effects). • Here it is assumed that the driving blow-up will be generated by beam-beam, damped by radiation damping.

  9. Beam-Beam Limits Luminosity(Blowing up the Unperturbed Vertical Emittance)

  10. LEP Result on Scaling with Energy

  11. Conclusion • Measured max. vertical beam-beam parameter: 0.083 • Fitted, achievable vertical beam-beam parameter at ~100GeV: 0.11 – 0.12 • Scaling with damping decrement:

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