Direct Simulation of Friction Forces for Heavy Ions Interacting with a Warm Magnetized Electron Distribution.

A proposed luminosity upgrade to RHIC includes a novel electron cooling section, which would use ∼55 MeV electrons to cool fully-ionized 100 GeV/nucleon gold ions. High-current bunched electron beams are required for the RHIC cooler, resulting in very high transverse temperatures and relatively low values for the magnetized cooling logarithm. The accuracy of analytical formulae in this regime requires careful examination. Simulations of the friction coefficient, using the VORPAL code, for single gold ions passing once through the interaction region, are compared with theoretical calculations. Charged particles are advanced using a fourth-order Hermite predictor-corrector algorithm. The fields in the beam frame are obtained from direct calculation of Coulomb’s law, which is more efficient than multipole-type algorithms for less than ∼106 particles. Because the interaction time is so short, it is necessary to suppress the diffusive aspect of the ion dynamics through the careful use of positrons in the simulations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]