Paper  Title  Page 

WEBX03  Modeling of Nonlinear Effects in RF Cavities  0 


Emerging accelerator applications require electron beam radii comparable to RF cavity apertures, placing more stringent demands on the modeling of particle motion in RF cavities using mapbased techniques. Highgradient cavities and cavities with significant axial asymmetries also demand improvements in modeling capabilities. A new method has been developed for computing highorder nonlinear maps for arbitrary RF cavities*. It has been implemented through fifth order in MaryLie/IMPACT, so simulations can include the effects of spacecharge. We describe this new approach and present comparisons with more traditional approaches.
* D. T. Abell, submitted to PRSTAB. 

WEBY05  Simulating dynamical friction in wigglerbased highenergy electron coolers, including finitetime effects  0 


The proposed RHICII luminosity upgrade includes a novel electron cooling section, using ~55 MeV electrons to cool fullyionized gold. We present simulations of the dynamical friction force exerted on the Au ions. Rather than a strong solenoid, a long helical wiggler magnet is used to provide focusing and suppress recombination. In the rest frame of the relativistic electron and ion beams, with nonrelativistic motion and electrostatic fields, the Lorentz transformed wiggler field yields strong, rapidlyvarying electric fields. The VORPAL simulation framework applies a semianalytic binary collision algorithm, in which ionelectron collisions are modeled pairwise. This model is combined with standard particleincell (PIC) techniques, through an operatorsplitting approach, to include the effects of external fields. Charge shielding due to electronelectron interactions is also included via PIC. Simulated friction results are compared with BETACOOL, which integrates the standard unmagnetized formulas. With finite interaction times and electron wiggle motion correctly included, we find good agreement with VORPAL. 