Download - LCLS-II Transverse Tolerances
LCLS-II Transverse Tolerances
Tor RaubenheimerMay 29, 2013
LCLS-II FAC Review, February 27-28, 2013
LCLS-II Accelerator Parameters
Slide 2
parameter symbol nominal range unit
Electron energy Ef 13.5 7.0 – 13.5 GeV
Electron bunch charge Q 0.150 0.01 - 1.0 nC
Pulse repetition rate f 120 SS, 1 - 120 Hz
Transverse slice emittance gex,y 0.4 0.15 - 1.2 m
Peak current Ipk 3.0 0.5 - 5.0 kA
Slice energy spread sE 1.4 0.1 - 1.5 MeV
LCLS-II Acc. Phys, May 29, 2013
Tolerance Specifications
• Transverse tolerances to minimize emittance dilution, optical errors and beam jitter
Tolerances based on most stringent conditions – usually 10 pC with 0.17 mm-mrad emittance and over-compression with 0.5% DE/E
Sources include alignment errors, magnet harmonics, PS fluctuations, component vibration, and coupling from other sources
Jitter tolerances set to limit beam motion to 33% rms in undulator from all sources
All tolerance specifications are rms values
• Full tuning / bump studies not completed
Slide 3
LCLS-II Acc. Phys, May 29, 2013
Transverse Jitter Sources
• Based on ge = 0.15 mm-mrad, N = 250 pC, sE/E = 0.5% and D/s<33%
Slide 4
(DI/I = 15%)
LCLS-II Acc. Phys, May 29, 2013
Comparison with LCLS-I Tolerances
• LCLS-I quad jitter tolerances were specified to limit the beam expected amplitude to 10% of the rms beam size.
The amplitude is sqrt(2) larger than the rms offset• LCLS-II tol. are specified for 33% rms jitter from all sources• Although not specified, it looks like LCLS-I tolerances were
specified for 1 mm-mrad versus 0.17 mm-mrad for LCLS-II LCLS-II total jitter budget is ~2x looser
• Quadrupoles are small fraction of jitter budget quadrupole jitter requirements are 1.7x tighter
Slide 5
LCLS-II Acc. Phys, May 29, 2013
Current and Energy Jitter Transverse
• Beam current jitter couples to transverse jitter through transverse wakefields and CSR
• Beam energy jitter couples to the transverse jitter through residual dispersion, coupling to wakefields in dispersive regions and changes in phase advance
Slide 6
Longitudinal Wakes for 250 pC, 3 kA
CSR Cancellation
Septum kick for 250 pC, 3 kA
LCLS-II Acc. Phys, May 29, 2013
Steering Correctors
• Largest potential source of beam jitter at ~20% DX,Y/sX,Y MCOR power supplies limited to ~1e-4 DI/I LCLS-I specified 3e-5 toelrances for many dipole correctors
• Sizes of MCORs reduced to balance corrector strength to reasonable values ease tolerances
• Used ‘reasonable’ maximum quadrupole alignment errors and compared to typical LCLS-I corrector strengths
Slide 7
LCLS-II Acc. Phys, May 29, 2013
Steering Correctors (2)
Slide 8
L1 / L2 values are < 10 G-mL3 values < 20 G-mBC2 values large
LCLS-II Acc. Phys, May 29, 2013
Steering Correctors (3)
• Maximum quadrupole misalignments for corrector sizing
Slide 9
LCLS-II Acc. Phys, May 29, 2013
Steering Correctors (4)
• Most correctors could correct a local large misalignment In some cases, multiple (2) correctors will be required
Slide 10
LCLS-II Acc. Phys, May 29, 2013
Steering Correctors (5)
• Not showing Tables – look in PRD!
• Most correctorsmuch weaker thanin LCLS-I specsbut similar to LCLS-I operatingvalues
• L1 / L2 / L3 correctors are all much weaker thanSLAC linac
• LTU sized at 60 G-m and dump correctors are 120 G-m
Slide 11
LCLS-II Acc. Phys, May 29, 2013
Dipole Magnets (1)
• Achromatic magnet strings should be largely insensitive to power supply fluctuations In practice, magnets are only matched at 1% level and include +/-
1% trims to match magnets• Power supply regulation tolerances calculated to limit (1)
change in path length, (2) transverse trajectory in achromat, and (3) transverse jitter due to 1% magnet mismatch Dipole string PS are medium PS with 5e-5 regulation Trim power supplies are standard MCORs with 2e-4 regulation
Slide 12
LCLS-II Acc. Phys, May 29, 2013
Dipole Magnets (2)
• Roll jitter tolerances vary between 1 and 10 urad Dipole roll jitter is 2nd largest DY/sY jitter source
• Roll alignment tolerance is set to limit dispersion errors and trajectory Dipole roll alignment tolerances vary between 0.3 and 5 mrad
• These may be overly tight and can iterate as needed
Slide 13
LCLS-II Acc. Phys, May 29, 2013
Quadrupole Magnets (1)
• Quadrupole vibration tolerances are the 3rd most important source of beam motion Typical values vary
between 100 and 50 nm
• Quadrupole alignment set loosely by increase in projected beam sizes Typical values range
bewteen 300 and 100 um
Without bumpsDe/e ~ 500%
Slide 14
LCLS-II Acc. Phys, May 29, 2013
Quadrupole Magnets (2)
• Quadrupole vibration tolerances tight in BC1, BC2, Bypass extraction and LTU – typical jitter contributions <1% magnet
• May want to work on S20 quadrupole supports
Slide 15
S20 and Bypass extraction LTUBC1 BC2
Vib
ratio
n To
lera
nce
[um
]
LCLS-II Acc. Phys, May 29, 2013
Quadrupole Magnets (3)
• Quadrupole power supply regulation tolerances are calculated to minimize (1) /Db b, (2) Dh*sE/E, and (3) jitter due to trajectory errors: 3e-5 DI/I minimum tolerance
• For jitter calculation assumed quadrupole center-to-trajectory of 100 um in BC2, Bypass ext. & Undulator; 200 um in BC1 & LTU; 1000 um in Bypass; 300 um elsewhere
Slide 16
Bypass extraction LTU Arc
LCLS-II Acc. Phys, May 29, 2013
Transverse TolerancesAlignment Tolerances
• Alignment numbers provide guidance beam-based tuning• Slice e impact is small
(slice = 1% of sZ)• Projected e impact is
large
• Calculated for over-compressed case with 0.5% DE/E• Alignment: 300 um on rf structures and most quadrupoles;
200 um in BC1 and LTU; 100 um in BC2, Bypass and Undulator X-band structure transverse wake is 40x larger than S-band yielding
30% projected De/e growth by itself
Slide 17
HXR (Proj) SXR (Proj.)DeX/eX DeY/eY DeX/eX DeY/eY
428% 496% 502% 590%
(slice De/e are ~2%)
LCLS-II Acc. Phys, May 29, 2013
Magnet Field Tolerances
• Detailed magnet tables for all dipoles, quadrupoles and steering correctors
• Multipole tolerances calculated using 250 pC (0.5 mm-mrad) over-compressed beam (0.5% DE/E) plus steering errors of 0.5 mm except 1 mm in injector, bypass and undulator
• Multipole tolerances are relatively loose except where there is dispersion Uncorrelated effect on beam core is small <5% De/e and <0.1%
DK/K Slide 18
Partial table for SXR LTU quads