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
disturbing nominal operations during the ‘quad-scan’. The two methods are complementary, and
the 3-PR system envisioned allows either method to be used.
7.8.1.2 ED1 Emittance Station
The ED1 station (Figure 7.19) is placed directly after BC1. It is crucial for the measurement
and empirical correction of dispersion errors generated in BC1. The BC1 chicane can also be
switched off to help isolate the different errors of BC1, L1, and DL1. Like ED0, ED1 is a
dedicated three-monitor (wire-scanners) emittance measurement section. At 250 MeV the rms
matched beam sizes are 80 µm on the two outboard monitors, and 40 µm on the middle monitor.
As in the case of ED0, three wire scanners will be used, and an OTR monitor will also be located
at the center location where a waist nominally exists.
7.8.1.3 L2-ED Emittance Station
The L2-linac is the most sensitive to orbit variation (note large emittance growth in Figure
7.15) and therefore can be expected to require frequent, perhaps daily, emittance optimization.
The L2-ED station is placed at the end of L2 (Figure 7.16). It is a space-constrained, four-profile-
monitor (wire-scanners) station with non-optimal phase advance and an expected emittance
resolution of ~10%. This section will be used to empirically minimize the wakefield emittance
dilution of L2. Due to space constraints, it is, at present, the least optimized system.
7.8.1.4 L3-ED Emittance Station
The L3-ED station (Figure 7.18) is composed of four existing sector-28 profile monitors
(wire scanners). The linac optics, however, change somewhat in this area for LCLS operation and
therefore a small modification to the existing scanner locations is called for. The first sector-28
scanner will be moved upstream by one cell (24 meters) and the last scanner will be moved
downstream by one cell. The LCLS optics then produce an average of 54° per plane between
scanners, which is nearly optimal. In fact, the statistical resolution of the SLC configuration is
also marginally improved (Figure 7.62: dots). The rms beam sizes are not identical at each
monitor; however, the phase advance between scanners provides nearly optimal statistical
measurement resolution. The L3-ED station will be used primarily to guide BC2 dispersion
corrections. Emittance dilution occurring within L3 (see Figure 7.17) is expected to be very small
due to the short bunch and small energy spread there.
7.8.1.5 ED2 Emittance Station
A final emittance measurement section (Figure 7.36) is included just upstream of the
undulator entrance. This section will be used to make precise adjustments to the final horizontal
and vertical beta functions (using quadrupoles QM33-36 of Figure 7.36) and to confirm and
optimize the final emittance immediately before the undulator. This emittance measurement
section is also used to diagnose potential emittance dilution arising in DL2 through dispersion
errors or CSR. Like ED0 and ED1, ED2 is a dedicated emittance measurement section, but with a
16-µm beam size at each monitor in both planes at 14.3 GeV. Four wire-scanners (and redundant
OTR monitors at one of these locations) will be used for the profile monitors.
A C C E L E R A T O R ♦ 7-91