LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

Charge (nC)
0.8
0.4
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
1.2 Charge Data
Linear (charge data)
Q e = 6.1 x 10 –5
0
0 0.040
1-2002
8560A90
Laser Energy (mJ)
100 MV/m
50° Phase
0.080
Figure 6.4 The measured charge extracted from a Cu photocathode as a function of laser energy
with 100 MV/m peak rf field and 50° laser injection phase.
QE (10 –6 )
20
10
0
1
4-2001
8560A93
y (mm)
0
–1
–2
0
x (mm)
2
QE (10 –6 )
0
1
(A) (B)
40
20
0
y (mm)
–1 –2
0
x (mm)
Figure 6.5 The measured quantum efficiency is plotted for a Cu cathode both before (A) and after
(B) laser cleaning. The error in the QE values is indicated by the green slices at the top
of each QE column.
6.2.2 Transverse Emittance Measurements
The history of the lowest emittance measurements for 1 nC of charge is summarized
Figure 6.6. The lowest emittances to date have been achieved with solenoidal emittance
compensated photoinjectors with the lowest measured values near 2 µm as described below.
These measurements are consistent with the predictions of tracking codes like PARMELA if the
physical parameters of the experiments are taken into account. PARMELA simulations also
indicate that emittances on the order of 1 µm should be achievable if the Gaussian temporal
6-10 ♦ I NJECTOR
2