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
adjustment of the integrated quadrupole gradient will be done during the manufacture of the
quadrupole, before it is installed.
The optical strength of the quadrupoles was one of the parameters that was optimized in order
to minimize the power gain length. The value chosen is 0.112 m -1 for a beam of 14.35 GeV, but
the minimum is very flat and a variation of up to 10% would not significantly affect the power
gain length. When the LCLS is run at an energy other than 14.35 GeV (e.g., at 4.5 GeV), the
strength of the quadrupoles will not be adjusted. At 14.35 GeV the averaged beta function is
about 18 m, whereas at 4.5 GeV it is closer to 7 m.
Each quadrupole magnet is installed on slides so it can be moved, remotely, in both
horizontal and vertical directions. This enables the quadrupoles to also serve as steerers. They
will be used, along with the separate electromagnetic steerers, in the beam-based alignment
procedure.
In the simulations that were run, the quadrupoles were placed in the middle of the break
section. In the final mechanical design, the quads will be displaced to allow for optimal use of the
break. Therefore, the final position of the quadrupoles will not be known until the mechanical
design for the inter-undulator diagnostics is completed. However their relative separation will not
change.
8.7.1 Quadrupole Mechanical Design
The space between undulator segments is very limited. The quadrupole design is very
compact; the length is only 50 mm with an aperture of only 11.3 mm. The quadrupole assembly is
shown in Figure 8.25.
Figure 8.25 Sketch of the permanent magnet quadrupole. Ten identical permanent magnet blocks
are used.
8-38 ♦ U N D U L A T O R