|
In high-energy colliders (such as
the LHC at CERN), particles are made to collide with each other to produce new
particles (like the Higgs) that could confirm theories such as super-symmetry.
However, when two beams of particles collide, the probability of collision and
annihilation is very small. The major interaction between the two beams of
particles is the electromagnetic interaction: each particle in one beam seems a
very nonlinear force due to all the particles in the other beam. This is the beam-beam
interaction.
Because of the highly nonlinear
nature of the beam-beam force, the beam-beam interaction (BBI) could disrupt
the trajectories of particles, thus rendering the colliders ineffective. It is
widely accepted that the beam-beam interaction is responsible for observed
performance limitations in present-day colliders, but the underlying mechanism
remains unknown.
In our work, in the Beam Physics
& FEL Laboratory, we have focused on the study of collective
instabilities in the beam-beam interaction, and have shown, for the
first time, that these collective instabilities are the most likely candidates
for the observed limitations. In particular we have developed a unique computer
code called cbi (for Collective
Beam-beam Interactions) that correctly and fully models the transverse dynamics
in the beam-beam interaction. This is a particle-in-cell (PIC) code that solves
for the beam-beam force self-consistently. Using this code we have been able to
obtain qualitative agreement with experiment: in particular we are able to
observe both kinds of instabilities (period-n oscillations and pitchfork
bifurcations) that have been observed in colliders around the world. This
code has been used to study colliders such as CESR at Cornell, PEP-II at
Stanford, and LHC at CERN.
In future work we plan to extend
the code to include the longitudinal dynamics, and use it to make quantitative
predictions for operating colliders.
Relevant References
- Luminosity-limiting coherent phenomena in electron-positron colliders, S. Krishnagopal, Phys. Rev. Lett. 76, 235 (1996).
- Studies of the beam-beam interaction for the LHC, S. Krishnagopal, M. A. Furman, W. C. Turner, Proceedings of the 1999 Particle Accelerator
Conference, New York, 1999; (IEEE, New York, 1999), p. 1674.
- Energy-transparency and symmetries in the beam-beam interaction, S. Krishnagopal, Phys. Rev. ST Accel. Beams 3, 22401 (2000).
|
