Plasma physics at the final focus of high-energy colliders

The plasma physics associated with intense electron and positron beams in high-energy colliders is discussed. The focusing and plasma oscillation of these beams are studied in the presence of an externally supplied plasma (a plasma lens) and in the self-consistent fields of the interpenetrating beams. A plasma lens can provide strong focusing of a beam by shielding the beam’s radial space-charge electric field and allowing it to self-pinch in its self-generated azimuthal magnetic field. The focusing force of a plasma lens can be equivalent to quadrupole magnet strengths of the order of hundreds of MG/cm. Theoretical and computational work characterizing the aberrations and final spot sizes possible with plasma lenses is presented. Furthermore, when the e+ and e− beams overlap at the interaction point (i.e., collide), they behave (temporarily) as a two-component plasma. The self-pinching or disruption of one beam by another in the e+e− plasma is modeled analytically and with two-dimensional particle-in-cell simulations.