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TPAT088 | Consideration of Relativistic Dynamics in High-Energy Electron Coolers | |
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Funding: Work supported by U.S. DOE grant DE-FG02-04ER84094. A proposed electron cooler for RHIC would use ~55 MeV electrons to cool fully-ionized 100 GeV/nucleon gold ions.* At two locations in the collider ring, the electrons and ions will co-propagate for ~13 m, with velocities close to c and gamma>100. To lowest-order, one can Lorentz transform all physical quantities into the beam frame and calculate the dynamical friction forces assuming a nonrelativisitc, electrostatic plasma. However, we show that nonlinear space charge forces of the bunched electron beam on the ions must be calculated relativistically, because an electrostatic beam-frame calculation is not valid for such short interaction times. The validity of nonrelativistic friction force calculations must also be considered. Further, the transverse thermal velocities of the high-charge (~20 nC) electron bunch are large enough that some electrons have marginally relativistic velocities, even in the beam frame. Hence, we consider relativistic binary collisions treating the model problem of two charged particles on a line, comparing nonrelativistic dynamics, marginally relativistic (in the Darwin approximation) and fully relativistic, with retarded potentials. *A.V. Fedotov et al., Proc. 33rd ICFA Advanced Beam Dynamics Workshop (2004), in press. |