Injector Requirements Ccile Limborg, SLAC November 3, 2003

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Injector RequirementsCécile Limborg,
SLACNovember 3, 2003

• Physics Performance Requirements
• Operating range of parameters
• Tolerances, Safety Factors
• Updated tuning for matching section
• Tuning with longer pulse
• Sensitivity
• LSC simulations
• Conclusion
• Documentation

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Objective

• ?projected lt 1.2 mm.mrad
• ?slice lt 1.0 mm.mrad for 80 slices out of 100
• ?slice (80) projected emittance for the core
  80 slices
• for 1nC, 10ps pulse at 135 MeV ,in the presence
  of jitter errors at 120Hz

Gun E (MV/m) ? Balance ?th
Solenoid Position Length Field
Solenoid 2 Position Length Field
Linac0-1 Position E(MV/m)
Linac0-1 Position E(MV/m)
Laser Parameters Longitudinal (length, rise time,
flatness) Transverse(r, uniformity, pointing
spot) Energy ? charge
19 parameters to optimize
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Simulations - Nominal tuning

• 1nC, 10ps, rlaser spot 1.2 mm
• Thermal emittance of 0.72 mm.mrad (assumes 0.6
  per mm radius)
• Finite rise time of 0.7ps (from 10-90 level)

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Sensitivity Studies Single parameter variation
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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Sensitivity Studies - Combination of Errors

• Using extreme values of parameters deviations
  meeting regulation specifications

26 possibilities 64 runs
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Operating Range and Sensitivity

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Tolerances Alignment and Laser Uniformity

• () combined with uniformity of QE

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First Linac Section Alignment

• Effects of Wakefields
• Position ?150 ?m maximum
• Angular 120 ?rad
• With alignment steering those requirements
  are easily met (BPM resolution 10 ?m )

At end beamline
At end beamline
2 increase level
2 increase level
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Requirements on Laser Pulse - Summary

? 120 ?m
? 240 ?m
? 480 ?m
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• Laser Quality Transverse Uniformity
• High frequency modulations get diluted , low
  frequency is the most damaging
• Slope across Spot
• Offset of center of gravity ? transverse
  wakefield in linac
• Criteria deterioration of slice emittance at
  linac entrance by less than 5
• or center of gravity off by less than
  100 ?m at linac entrance
• Result No more than /- 15 (/- 10 feasible
  and will be the tolerance)

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• Laser Quality Transverse Uniformity
• Checker board type low frequency is worst
  case 1
• Generates ellipticity but no centroid offset
• Generates slice emittance growth
• Result maximum / 15 modulation
• (again 10 feasible and is the specification)

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• Example of high frequency structure

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Laser Quality (ignoring LSC)

• Longitudinal Flat top Flatness
• Emittance deterioration
• Result
• For ?gt 240 ?m , Modulation lt 20
• For 240 ?m lt ?, Modulation lt 30

Case of ?? 480?m Modulation 20
? 120 ?m
? 240 ?m
? 480 ?m
20 peak-to-peak
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Updated tuning - 135 MeV

• Final energy 135 MeV
• Linac-02 at 24 MV/m instead of 28.7 MV/m
• to prevent dark current at end L0-2 (noise on
  OTR screens)
• No emittance growth at 135 MeV
• Limit checked to be 120 MeV for emittance growth

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Updated tuning - add quadrupoles in L01-to-L02

• Modification of beamline
• Added two quadrupoles between L0-1 and L0-2
• Justification
• Beam sizes too large at exit L0-2
• PARMELA simulations had been misleading
• Showing artificially small beam sizes
• (problem of sampling in linac section,
  introduced by too large time steps)
• A Solenoid cannot provide the necessary focusing
  
• Provides even more tuning flexibility

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Updated tuning - add quadrupoles in L01-to-L02

Add 2 quadrupoles in the 1m drift between L0-1
and L0-2
PARMELA With Space Charge
Matching Section
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Tuning with longer laser pulse

• Objective
• Decrease emittances (slice, 80) to have larger
  margin for emittance growth
• as more compression possible from BC1 (thanks to
  laser heater)
• Explanation
• Smaller thermal emittance by reducing spot size
  radius
• Issues
• Strong Non-linearities in longitudinal phase
  space?
• Sensitivity increased (injection phase, solenoid
  fields , transverse wakes)?
• Difficult to compress ?
• Changes laser requirements ?
• First tunings (15 ps, 17.5 ps, 20 ps)
• Very good slice emittance
• Strong compression in gun (helps on 1.)
• More sensitive to injection phase (still well
  within tolerances)
• Matching not as good, but compression does not
  seem yet to present any problem
• Still To be checked
• Transverse wakefields

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Tuning with longer laser pulse
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Sensitivity Comparison case of 17.5 ps with
nominal 10 ps tuning
Solenoid Field Same sensitivity
Gun field Long pulse tuning less sensitive
Injection Phase Long pulse tuning more sensitive
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LSC (Longitudinal Space Charge ) Instability

• Plasma oscillation in a coasting beam

Current Density
Energy

• The self-consistent solution is the space charge
  oscillation

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LSC (Longitudinal Space Charge ) Instability

• Comparison with theory in drifts
• Good match for energy
• Simulations in gun

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LSC Simulations in gun
20 ? 14 rms 10 ? 7 rms 5 ? 3.5 rms

• Limitations of PARMELA
• Difficulties to study LCLS pulse
• Study of ? 50 ?m , dz 5 ?m
• ?z 5 mm
• Nz x Nr 1000 x 20
• 200k particles
• Per longitudinal bin 200 particles , 1/?200 7
• ? For initial modulation of less than 7
  modulation of current density at gun exit is in
  noise
• Case studied
• ? 50 ?m, 100 ?m, 250 ?m, 500 ?m, 1000 ?m
• For /-10 and /- 20 initial modulation
  amplitude

Noise Level 4 From uniform distribution
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LSC Simulations in gun

• Other cases under study for a shorter pulse than
  the LCLS pulse for 5 ptp
• Modifications to ASTRA to improve statistics
• Weight on particle charge
• Adaptative meshing (for higher density of
  particles)
• Can study modulation on core of bunch without
  introducing edge effects
• Objective give definitive specifications for
  flatness of flat top of laser pulse ( assuming
  laser heater will be on)

gun
drift
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CONCLUSIONS

• Tolerances on components well understood
• Wakefield studies under way
• Very promising preliminary results new tuning (
  Long pulse)
• More sensitivity studies
• Start-to-End simulations
• LSC
• Theory and simulations at advanced stage
• Understanding laser pulse requirements in the
  presence of laser heater

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DOCUMENTATION

• Nominal tuning
• 1 Sensitivity studies for the LCLS
  PhotoInjector Beamline , FEL03 conference
• 2 New tuning at 135 MeV , LCLS-INJ Note
• New tuning
• 3 Tuning with longer pulse , still to be
  written
• LSC
• 4 LSC Instability S2E simulation Workshop ,
  August 03, Berlin

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DOCUMENTATION

• Diagnostics
• 6 Gun Spectrometer C.Limborg , March 03
  updated October
• 7 Gun Spectrometer, Revision 1, C.Limborg,
  LCLS-InJTech Note
• 8 Gun Spectrometer, Revision 2, C.Limborg,
  LCLS-InJTech Note
• 9 Straight-Ahead Spectrometer, C.Limborg,
  April 03, LCLS-InJTech Note
• 10 Straight-Ahead Spectrometer, Revsion 1,
  C.Limborg, Oct03, LCLS-InJTech Note

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• BACK- UP
• SLIDES

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Tuning with gun unbalanced by -20 in ½ cell

At gun exit
At Linac 0-2 exit

• Field in 1/2 cell 80 of field in full cell
• ?projected 0.91 mm.mrad
• Small degradation compared balanced case
• ?projected 0.80 mm.mrad
• (1nC,10ps,0.5ps rise time,?th 0.3 mm.mrad)
• Only Solenoid field change by 3.5
• Bfield 2.61 kG instead of 2.71 kG
• Changing ?gun does not improve
• At entrance booster ?E 500 keV

At entrance Linac 0-1
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Physics Performance Requirements

• Charge
• 7 ok , objective 5
• Laser Spot Size
• 1 very easy to maintain

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Physics Performance Requirements

• Laser Quality
• Longitudinal Flat Top Flatness
• Source of CSR in BC2 if modulation in range 100?m
  lt ? lt200 ?m
• Result favorable situation since good dilution
  for short wavelengths (? lt 240 ?m )

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Physics Performance Requirements

• Alignment Linac Section
• Head-to-Tail Offset at entrance Linac
• Result /- 50 ?m

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Physics Performance Requirements

• Alignment Solenoid Tilt
• Creates centroid offset and angle (but can be
  corrected by steering)
• Creates slice emittance increase
• Criteria
• ??slice (80) at entrance Linac does not
  increase emittance by more than 1
• Head-tail centroid offset less than 100 ?m at
  entrance linac
• Result 1.5 mrad maximum
• No problem with offset of centroids, no problem
  in angle either

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Physics Performance Requirements

• Alignment Solenoid Offset
• Creates offset and angle of bunch (can be
  corrected by steering)
• Creates head-tail centroid offsets and angle
• Criteria
• ??slice (80) at entrance Linac not increase by
  more than 1
• Head-tail centroid offset less than 100 ?m
• Result 500 ?m maximum

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Physics Performance Requirements

• Alignment Laser Position Steering
• Creates offset and angle of bunch
• Creates head-tail centroids offsets and angles
• Creates slice emittance growth
• Criteria
• ??slice (80) at entrance Linac not increase by
  more than 5
• Head-tail centroid offset less than 100 ?m
• Result 100 ?m

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Physics Performance Requirements

• Alignment Laser Position Steering

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Solenoid 98 A
Data
Parmela
DUVFEL EXPERIMENT Good match of Slice Emittance
and Twiss Parameters Parameters 200 pC
Solenoid 104 A
Solenoid 108 A