  A magnetic bunch compressor has been designed and is being commissioned for
the APS linac to provide higher peak current for the LEUTL FEL. Of primary
concern is control of emittance growth due to coherent synchrotron radiation
(CSR). In addition, tolerances must be carefully evaluated in order to choose
the most stable operating conditions and ensure that the system can meet
operational goals. The computer code ELEGANT was used to design the bunch
compressor, set tolerances, and simulate likely performance. This 6-D code
includes a fast, simple simulation of CSR effects as well as longitudinal and
transverse wakefields. It also is believed to be unique in allowing
optimization of actual tracking results, such as bunch length, energy spread,
and emittance. Automated setup and analysis of matching and tolerance
simulations allowed consideration of numerous configurations without excessive
effort. This permitted choosing configurations that reduce sensitivity to
errors. Simulations indicate that emittance growth should be tolerable for up
to 600 A peak current, for which the normalized emittance will increase from 5
to about 6.8 pi-um. The simulations also provide predictions of emittance
variation with chicance parameters, which we hope to verify experimentally. *
Work supported by the U.S. Department of Energy, Office of Basic
  Energy Sciences, under Contract No. W-31-109-ENG-38.
