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 stages used to position the apertures will have positioning precision < 10 µm and angular
precision of < 1 mrad.
Attenuator
Some experiments require a local attenuator for calibration and to prevent damage to
sensitive components during alignment. The local attenuator will have a design very similar to the
solid attenuator located upstream in the Front End Enclosure (see Section 9.2.2.1).
Beam Intensity Monitors
Beam intensity monitors are required to measure the absolute flux incident on the samples
and the amount of flux transmitted through the samples. These monitors will be of the ion
chamber type described in the facility diagnostics section (Section 9.4.2.3).
Sample Chamber
The sample chamber in Hutch A2 will be instrumented for studies required to characterize the
interaction between the FEL pulse and matter. In addition to sample holders and photon
spectrometers, it will include electron and ion time-of-flight spectrometers.
Beam Stop
At the back end of Hutch A2 is an insertable beam stop with integral burn-through detector.
9.2.2.4 Hutch A4
Hutch A4 will initially be used for commissioning diagnostics, which will be housed in a
diagnostics tank. See Section 9.4.2.
Fixed Mask and Beam Stop
At the back end of Hutch A4 is an insertable beam stop with integral burn-through detector.
Behind the beam stop is a fixed mask with 4.5 mm diameter aperture, identical to the fixed masks
in the Front End Enclosure. As with those masks, its purpose is to cut the divergence of the
spontaneous radiation, so that all transmitted radiation remains within the beam pipe. The
coherent FEL radiation cannot strike this mask, and so peak power is not a concern.
9.2.2.5 Inter-Hall Transport
A beam pipe connects the two main halls through a tunnel. It is about 250 m long. Access
will be available along the length of the tunnel. In the center of the tunnel, a diagnostics tank will
permit beam intensity and position measurements.
9.2.2.6 Hutch B1
The first hutch in Hall B will contain optical elements, which condition the x-ray beam for
the Hall B experiments (see Figure 9.14). Only one such element will be included in the initial
LCLS, though space is made available for future optics. Hall B is intended primarily for
experiments, which prefer to be far from the source, in order to reduce the peak intensity or to
allow focusing to a minimum spot size.
9-20 ♦ — R A Y B E A M T R A N S P O R T A N D D I A G N O S T I C S