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 7.40 Horizontal position, x, without CSR (left) and with CSR (right), versus z, for the LCLS
bunch profile (i.e., tracked through upstream systems) after DL2 bends. Projected
emittance growth is 2.5 due to CSR in BC2, but dominated by bunch head and tail.
7.5.2.3 Beam Size, Aperture, and Field Quality
The beam size in DL2 reaches a peak value of ~50 µm. A 2.5-cm full aperture is, therefore,
completely adequate. The large dispersion in the DL2 quadrupoles sets the tolerances on field
quality and gradient errors. Table 7.20 lists dipole tolerances, while the alignment and field
strength sensitivities for quadrupole magnets in the DL2 area are shown in Figure 7.41. Each
sensitivity shown corresponds individually to a filamented x and y emittance dilution of
∆εx/εx0 + ∆εy/εy0 = 2%.
Table 7.20 Dipole magnet tolerances for DL2 with an exaggerated 0.05% rms energy spread. Field
harmonics are evaluated on a 20-mm radius and each entry individually corresponds to a 2%
emittance dilution.
Magnet Quantity Roll Angle [mrad] |b1/b0| [%] |b2/b0| [%]
B31-B34 4 80 2.1 100
VB1 & VB2 1 each 170 5.4 100
The most challenging of these sensitivities are the absolute gradient errors of some of the
quadrupoles, |∆b1/b1| < 1.5%. Although many of these magnets are powered in series, their
gradients may differ slightly due to construction errors. A tolerance of