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 collimator will be nominally open with a full horizontal gap of ~6 cm, but each jaw will be
independently controlled in order to select any energy band. The collimator will be very useful in
diagnosing tails in the electron beam. It is not envisioned that any significant collimation will be
made during normal LCLS operations. This might otherwise introduce an intolerably large pulse-
to-pulse charge jitter or wakefields within BC2.
∆x,∆y (mm)
∆b 1 /b 1 (%)
1
0.1
10
1
Q24701
WIGGLER
QM21
B21
CQ21
B22
400 405 410
S (m)
415 420
Figure 7.31 Alignment (top: black is x, and green/white is y) and gradient sensitivities (bottom) for
BC2 quadrupoles. Each bar individually corresponds to a ‘filamented’ emittance dilution
of ∆ε x/ε x0 + ∆ε y/ε y0 = 2%.
7.4.2.7 Tuning and Correction
Dispersion errors (typically in the horizontal plane) may be generated by small quadrupole
field components in the center two dipoles of the chicane (see Table 7.15). A pair of small
correction quadrupoles are included in the chicane with the first quadrupole (CQ21) placed near
the end of B21 at ηx ≈ 139 mm, βx ≈ 65 m, and the second (CQ22) just upstream of B24
(ηx ≈ 41 mm , , βx ≈ 4 m). Two orthogonal linear combinations of these quadrupoles can then be
used to correct up to ~250% horizontal emittance dilution due to dispersion errors. Since the
dispersive beam size at these two quadrupoles is ηxσδ ≈ 1 mm and 310 µm, respectively and the
betatron beam size is much smaller at (βx,yεx,y) 1/2 < 86 µm, these quadrupoles have little effect on
the final beta functions. The specifications for these correction quadrupoles are given in Table
7.16 and their locations are shown in Figure 7.26.
The four main dipoles of the chicane will be powered in series with one power supply so that
field regulation tolerances are met (see Table 7.4). The rms regulation tolerance for this main
supply is 0.05%. Trim coils will be included in each BC2 main dipole for compensation of
magnet-to-magnet construction errors in the dipole field strengths. This will also allow some
horizontal steering. In addition, vertical dipole correctors will be included nearby to facilitate
vertical steering.
B23
CQ22
B24
QM22
Q24901
A C C E L E R A T O R ♦ 7-53