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
deflection in the "Y" direction for one of the model cases where the force was distributed along a
line corresponding to the location of the magnetic jaws; the maximum deflection is 7.19 µm.
Figure 8.19 Calculated deflection of the titanium bar due to the magnetic forces.
8.6.2 Provisions for Magnetic Tuning
The magnets and poles of each jaw are assembled onto a base plate of aluminum, as
mentioned above. The base plate for each jaw consists of five blocks placed end to end with three
long blocks approximately 1-m long in the middle and a shorter block at each end. The design
allows precision shims of various thicknesses to be placed between the core and jaw blocks in
order to achieve precision tuning of the undulator segment. A series of these shims in 2-micron
increments is being made for this purpose by precisely nickel-plating brass shims. There is also a
design provision to achieve the same results using "push-pull" screws.
The magnetic structure can also be magnetically tuned using low carbon steel screws, referred
to as side shims, which can be screwed in towards the poles in order to divert some of the
magnetic flux and decrease the field under the pole. These side shims can be installed anywhere
along the length of the undulator segment as required for precise tuning. The shim block
assembly is shown in Figure 8.20.
The two end blocks of the base plate for each jaw can also be bent slightly, up to 80 microns,
in order to change the gap at the end of the undulator segment. While this provides another means
of tuning the undulator field strength, its primary function is for adjusting the phasing between
the undulator segments. For this purpose, four PZT (Lead Zirconate Titanate) translators are
housed inside holes within the titanium core as shown in Figure 8.21. The resolution of these
translators is on the sub-micron level allowing very precise tuning of the undulator taper.
U N D U L A T O R ♦ 8-33