LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

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Figure 6.25 Transverse distribution in the x-x' plane of particles in a slice (red/light) at the exit of
L0 for 100K particles shown against a background of the full projection (blue/dark). Scales are the same
as for the upper right plot of Figure 6.24. In each plot read left to right, the location of the slice along
the z-axis of the bunch can be identified by the corresponding asterisk in the lower right plot of
Figure 6.24.
The longitudinal distribution of particles at the exit of L0 is shown in Figure 6.26. The
energy as a function of axial position within the bunch is shown in the upper left with the
corresponding particle distributions projected out from both planes shown in the upper right and
lower left. The lower right distribution is the same as the lower left, but in terms of peak current
instead of number of particles, and time instead of axial position.
The rms energy spread of the distribution shown in the upper right of Figure 6.26 is
σγ γ o = 0.18% . The L0-2 phase is set such that when the wakefields are included the total
energy spread will be minimized. The effects of longitudinal wakefields in the booster are
calculated using the 2D simulation code LiTrack (see Section 7.2.5, 2D Tracking Studies) with
the PARMELA results at the exit of L0 as input. The rms energy spread in this case is reduced to
0.1%. As indicated in Section 6.1.1, Beam Requirements, a low value of slice energy spread is
also desired. The slice energy spread is plotted as a function of axial position in Figure 6.27. It
can be seen that for the core of the distribution the slice energy spread is σγ slice γ o < 0.005% .
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