LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

L C L S C O N C E P T U A L D E S I G N R E P O R T
Figure 7.49 Beam and FEL evaluation of the sliced beam at 14.35 GeV using 80% of beam core.
The dotted lines represent the bunch-length-integrated values, which are irrelevant.
7.6.3 Beam Jitter Simulations
Full start-to-end jitter simulations have been performed using the tightest (bold) tolerances
from Table 7.5 and repetitively tracking the entire system while varying machine parameters
such as charge, gun timing, rf phases, and rf voltages, etc. The gun-laser timing jitter is reduced to
0.5 psec here (as compared to 0.7 psec in Table 7.5) to reduce the final energy jitter level from
0.1% to 0.06% rms. The simulations apply repeated 6D particle tracking, with 10 5 macroparticles
per tracked beam pulse, using the computer codes Parmela [11], Elegant [10], and Genesis [39].
No misalignments are added, so the effects of transverse wakes are not yet included here.
Parmela is used to simulate the photoinjector, ending at 150 MeV, because it includes space
charge forces, which are important in the gun and L0-linac. Elegant is used for the remainder of
the linac, ending at the entrance to the undulator. The macroparticle output of Parmela is used
directly as input to Elegant, which is a 6-D tracking code that includes rf curvature effects,
longitudinal and transverse wakefields of the accelerating structures, coherent synchrotron
radiation, incoherent synchrotron radiation, and chromatic effects in quadrupoles and dipoles.
Elegant ignores space-charge forces, which is acceptable because of the high beam energy
beyond the 150-MeV injector.
A C C E L E R A T O R ♦ 7-75