Beam Dynamics Justifications of modification of Linac structures C.Limborg-Deprey

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Beam Dynamics Justifications of modification of
Linac structuresC.Limborg-Deprey

• Parameter goals for the LCLS injector
• Dipole moment
• in L01
• in L02
• Quadrupole moment

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6 MeV ?? 1.6 ??m ??,un. 3keV
63 MeV ?? 1.08 ??m ??,un. 3keV
135 MeV ?? 1.07 ??m ??,un. 3keV
135 MeV ?? 1.07 ??m ??,un. 40keV
Linac tunnel
Laser Heater
DL1
Gun
S1
S2
L0-1 19.8MV/m
L0-2 24 MV/m
Peak Current 100 A
Charge 1 nC
?projected,?slice ? 1.2,1 ??m.rad
Repetition rate 120 Hz
UV Laser 200 ?J, ? 255 nm, 10ps, r 1.2 mm
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Errrors
Nominal tuning Q 1nC,10ps??th 0.72
mm.mrad, rlaser 1.2 mm
Solenoid 1 ?0.3
Egun ?0.5
?gun ?2.5 ?
Balance 3 is ok
Linac Field 12 (EFinal 150 MeV )
Solenoid 2 20
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Combination of errors

• Using extreme values of parameters deviations
  meeting regulation specifications
• Design for 1nC operation even if other operating
  points are being investigated

Param. Nom. Units Stability Requirement
Sol1 2.7235 kG ? 0.02
Sol2 0.748 kG ? 1
Gun Phase 27.25 ? ? /0-X ? 0.1?
Gun Field 120 MV/m ? 0.5
Charge 1 nC ? 5
L01Field 18 MV/m ? 2.5
26 possibilities 64 runs
?? Cannot afford additional emittance growth
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S-Band linac structure

• Correction of amplitude term
• with offset of cell
• No correction of phase term
• See J.Schmerge talk
• and Blue Book P 147, P191

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L01 entrance coupler

• Dipole
• time dependent head-tail kick, integrated over
  the entrance cell and two first full cell
  (see Z.Lis talk)
• 10ps bunch, Phase close to crest , 18MV/m
• ??(???) ?? 2.5.10-3
• ?? increase
• with ??? rms of head-tail kick

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L01 entrance coupler
Rms a 10 ps long bunch
Vrf 18 MV/m
Crest 0
a 10 ps long bunch
Max min for a 10 ps long bunch
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L01 coupler
PARMELA simulations of misalignment including
transverse wakefield show similar magnitude 200
??rad ?? ? ??? 2.4.10-3 ? 4 increase
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L01 exit coupler
The emittance growth will not exceed 1 at the
exit of L01
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L02 entrance coupler
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L02 exit coupler
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Quadrupole moment
Quadrupole moment in L01 entrance
for 10 ps
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Conclusion

• Dual Feed mandatory for both L01 and L02 input
  couplers
• output couplers do not absolutely require dual
  feed
• Racetrack shape of entrance cell is mandatory for
  both L01 and L02