1. Single Side Coupler for input coupler of L0-1
Jan27-04
Agenda:
C.Limborg
Tolerances based on maximum emittance growth
Review of Blue book analytical computation
Zenghai Li
Computations with S3P of angular kicks from single side input coupler
Discussion of geometry
define dual coupler geometry to be run by Zenghai
Discussion on other studies
gun dual feed, gun geometry, wakefields at first iris

2. Reminder:
The 80% emittance is around 0.9 mm.mrad
Tolerance : No more than 1-2% growth from Head-Tail & Wakefield effects
Linear Head-Tail kick at entrance of L0-1
No Solenoid, No Wakefield
With Solenoid, No Wakefield

3. First Linac Section Alignment: Wakefield effects
Effects of Wakefields (ignoring ):
Position : 150 m maximum
Angular :  120 rad maximum
Position Misalignement
150 m maximum
Angular Misalignment
 120 rad
~2% increase level
~2% increase level
At end beamline
At end beamline

5. “PHASE TERM”
In phase with force Fz
Centroid deflection if field on crest
“AMPLITUDE TERM”
In quadrature with force Fz
Strong Head-to-tail effect if field on crest
Without cavity offset :
With cavity offset :
determined from microwave perturbation measurements , but conditions are not described in blue book

6. Without Cavity Offset
Amplitude term dominant (around crest)
With Cavity Offset = Amplitude term corrected but not phase term (which becomes dominant beyond +/- 20 degrees off crest)

7. Conclusions:
Tolerance is 120 rad for a 10 ps bunch (due to wakefields along the structure)
Without cavity offset , amplitude term is dominant with a 1.2 mrad head-to-tail differential kick when cavity operated around crest
With the cavity offset, only amplitude term is corrected. The amplitude of the head-to-tail is now small enough around crest for a 10 ps bunch, however we want to be able to operate :
at least +/- 40 degrees off-crest
run ~20ps bunch l
This result is based on the 0.1% factor measured many years ago (in conditions that we ignore in particular for the field gradient)
For all those reasons a numerical computation was needed