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 tolerances of Table 7.5 apply only for pulse-to-pulse jitter, which is too fast to be
corrected with fast feedback systems. For variations slower than a few seconds, such as those
induced by a temperature change, it is quite simple to hold the beam energy constant in each bend
system by monitoring a few beam position monitors (see Section 7.8.4). It is also possible to hold
the bunch length constant after each of the two compressors by employing a bunch length
monitor (see Section 7.8.2) and feeding back on both rf phase and voltage upstream of the bends.
Table 7.4 Individual rms sensitivities (p sen) each cause a +12% peak current change (column 3) or
+0.1% electron energy change at 14.35 GeV (column 4). All sensitivities listed are
approximately linear. These are not tolerances, but individual sensitivities used to form a
tolerance budget.
Parameter Symbol ∆I/I 0 = +12% 〈∆E/E 0〉 = +0.1% Unit
mean L0 rf phase ϕ0 +0.67 −3.6 S-band deg
mean L1 rf phase ϕ1 +0.16 † −0.24 †
S-band deg
mean LX rf phase ϕx −1.1 +12. X-band deg
mean L2 rf phase ϕ2 −0.22 ‡ +0.36 ‡ S-band deg
mean L3 rf phase ϕ3 >+20 +0.47 S-band deg
mean L0 rf voltage ∆V0/V0 +0.29 −0.33 %
mean L1 rf voltage ∆V1/V1 +0.33 −0.34 %
mean LX rf voltage ∆Vx/Vx −1.5 +1.9 %
mean L2 rf voltage ∆V2/V2 −1.0 +0.64 %
mean L3 rf voltage ∆V3/V3 >+20 +0.15 %
Gun timing jitter ∆t 0 −1.8 +1.3 psec
Initial bunch charge ∆Q/Q 0 −5.6 −46. %
BC1 chicane ∆B1/B1 −0.15 +0.17 %
BC2 chicane ∆B2/B2 +0.76 +0.69 %
Initial bunch length ∆σz/σz 0 +5.3 −37.8 %
common L1/LX timing ϕx=4ϕ1 +0.43 −0.26 S-band deg
common net phase ϕ0=ϕ1=ϕx=ϕ2=ϕ3 −4.0 +1.4 S-band deg
† The L1 phase sensitivities become 0.47˚ and 1.6˚ (left to right) if BC1 energy is held constant.
‡ The L2 phase sensitivities become 0.36˚ and 2.7˚ (left to right) if BC2 energy is held constant.
The tolerances are quite tight for many of the parameters, especially those systems driven by
a single klystron (e.g., L1). Since the rf tolerances represent a demand on the average phase or
average voltage over the klystrons of that linac, multiple-klystron linacs such as L2 and L3
A C C E L E R A T O R ♦ 7-19