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


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%)


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


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


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


Steering Correctors (2)

Slide 8

L1 / L2 values are < 10 G-mL3 values < 20 G-mBC2 values large



• Maximum quadrupole misalignments for corrector sizing

Slide 9



• Most correctors could correct a local large misalignment In some cases, multiple (2) correctors will be required

Slide 10



• 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


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


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


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



• 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

]



• 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


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%)


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

Documents

LCLS-II Transverse Tolerances