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
The quadrupole is designed in such a way that top and bottom halves of the assembly are
symmetrical about the beam center. The outer housing of the assembly is fabricated from low
carbon steel, thus providing a complete magnetic shield on all six sides. The top and bottom
housing sections are fitted with aluminum inserts used to define the location of the magnets and
poles. These sections, once fitted with the aluminum inserts, are precisely machined together side
by side to ensure that the holders and inserts end up in the same plane. Similarly, the two carbon
steel side shields are clamped together and precisely ground, thus creating two identical halves.
As a result of this machining approach, the assembly, once bolted together, precisely defines the
X and Y-dimensions (the Z-dimension is the beam direction). These in turn determine the gaps
for the poles and magnets.
In the center of the four poles are the two central magnets. On the outside of each pole are
pairs of magnets located side by side. Each of the magnets is slightly larger than the neighboring
poles and overlaps the poles on three sides. All of the magnets in the assembly are the same size;
thus, the outer magnet pairs are twice the thickness of the inner magnets.
Each end of the quadrupole assembly is fitted with a shield that has a 20-mm wide groove
that allows insertion of a Hall probe for magnetic measurement purposes. The two side shields
each contain a pair of precise holes in the median plane that are used to house standard tooling
balls for alignment of the assembly in the beam line.
The quadrupoles are supported by the same Anocast ® piers as the BPM modules but
otherwise not coupled to them. Their transverse position (horizontal and vertical) can is remotely
controllable by x,y-slides. The quadrupoles have a bore of 11.5 mm and thus provide plenty of
aperture for the 6 mm OD vacuum chamber to fit without interference. There will be horizontal
and vertical corrector coils connected to each quadrupole.
8.8 Vacuum Chamber
The undulator vacuum chamber is 120 meters long and must fit into the 6-mm undulator gap.
The chamber will be segmented in the same way as the undulator with a diagnostics section
between each undulator segment. It will be pumped by ion pumps at each diagnostics chamber.
The diagnostics chambers need to be designed with a relatively smooth bore to minimize
wakefields.
The proposed chamber through the undulator segments is formed from a stainless steel tube
with copper plating on the inside to reduced the resistivity as seen by the beam. The following
analysis shows that such a chamber can meet the LCLS requirements and withstand missteering
events. It cannot withstand continuous missteering into the wall for extended periods of time. The
Machine Protection System will prevent this.
U N D U L A T O R ♦ 8-39