Alternate Lattice for LCLS-II LTU Y Alternate Lattice for LCLS-II LTU Y. Nosochkov LCLS-II Physics Meeting, March 21, 2012

Goals The original LTU vertical separation scheme does not cancel the vertical dispersion resulting in several cm leaking dispersion downstream of the SXR LTU  Cancel dispersion by modifying the separation scheme and the optics Several LTU magnets interfere with the LTU wall and LCLS-I  Reduce interference by changing magnet positions Keep the number of magnets within the present budget 3/21/2012 Y. Nosochkov

Original lattice HXR Undulator LTU Linac Bypass  sz sd 3/21/2012 SXR µ BC2 BC1 gun DL1 DL2 11-3 to 14-4 14-7 to 20-4 11-1  sd sz 3/21/2012 Y. Nosochkov

Original LTU HXR SXR 2.4o 4-bend 4 wires, 4 collimators 45o FODO Septum 2.4o 4-bend 1.2o 3/21/2012 Y. Nosochkov

Original vertical separation scheme Kicker strength = 0.07 kGm at 15 GeV P. Emma 3/21/2012 Y. Nosochkov

Lambertson septum in the original scheme P. Emma 3/21/2012 Y. Nosochkov

Kicker vertical dispersion is not canceled Y-orbit bump Y-dispersion in the LTUS Y-dispersion in LTUS through dump 3/21/2012 Y. Nosochkov

Canceling the kicker dispersion Dispersion correction cannot be delayed because of the downstream SXR diagnostic section. Using 2 more correctors (2nd kicker + 3rd DC bend) results in large Y-orbit in quads (up to 20 mm) and large corrector strengths (up to 2.7 kGm). This is in part due to small vertical phase advance in the LTU triplet optics. Large orbit when Y-dispersion is canceled with 2 kickers and 3 DC bends septum Various options were tried: adding quads to the triplet system, using 2 bumps (180° apart), FODO cells, doublet cells, horizontal separation. The selected option: 1) Doublet DF-FD cells, 2) horizontal beam separation, 3) two 1.2° bends instead of four 0.6° bends (more free space and fewer quads), 4) SXR diagnostic with 90° FODO cells (fewer quads as compared to 45° cells). Disadvantages: a little higher synchrotron radiation effect due to stronger bends, fixed R56 in the 2.4° arc (but an additional tuning chicane could provide adjustment). 3/21/2012 Y. Nosochkov

Original SXR LTU Alternate SXR LTU Replace LTU triplet cells with DF-FD cells matched to 180o x-phase between bends. Replace 4x0.6o bends with 2x1.2o bends for fewer arc quads and larger quad spacing. Use horizontal separation, include the kicker orbit into the SXR reference trajectory. Y-kicker DC1 DC2 septum 2.4o 4-bend 1.2o 2-bend Original SXR LTU Long drift to maximize HXR/SXR separation Long drift to minimize wall interference septum 2.4o 2-bend 1.2o 2-bend X-kicker DC1 DC2 Alternate SXR LTU Low bx at bends 3/21/2012 Y. Nosochkov Kicker strength = 0.17 kGm at 15 GeV and Dx=-10mm

Kicker orbit septum kicker QDL44 BX42 QDL45 QDL46 QDL43 X = -10 mm at septum Off-axis through QDL44,45,46 and BX42 3/21/2012 Y. Nosochkov

First look at the current sheet septum design for horizontal separation (C. Spencer) SXR HXR Assume 10 mm beam-to-beam separation, B=2.6 kG, L=2 m. Some HXR correction will be required to compensate for residual field. 3/21/2012 Y. Nosochkov

Geometry: original 4-bend arc versus alternate 2-bend arc 19.6 cm Wall Original: some magnets interfere with the wall Alternate: only beam pipe interferes with the wall 3/21/2012 Y. Nosochkov

SXR diagnostic and 2nd dogleg bend pair Original 120o b-waist diagnostic w cx,cy triplets 90o FODO diagnostic 2x90o FODO w cy cx Alternate 3/21/2012 Y. Nosochkov

Normalized beam X-phase space at LTUS wires Wire phase separation: mx : 65°-25°-65° x= 14 m ax= ±1.43 3/21/2012 Y. Nosochkov

Normalized beam Y-phase space at LTUS wires Wire phase separation: my : 25°-65°-25° y= 14 m ay= ±1.43 3/21/2012 Y. Nosochkov

SXR dogleg geometry: original versus alternate 19.3 cm 3/21/2012 Y. Nosochkov

Complete alternate LTU lattice 2.4° HXR 45° FODO diagnostic 2.4° 1.2° -1.2° SXR 90° FODO diagnostic Septum 3/21/2012 Y. Nosochkov

Complete alternate LTU geometry septum Panofsky Red -- bends, blue -- quads, green -- x-kicker, septum, DC bend V-bend 1st Panofsky quad separation: 237 mm HXR SXR Downstream of the LTU the HXR/SXR geometry is matched to the original geometry 3/21/2012 Y. Nosochkov

LTU wall: original lattice Interference: 3 quads + 2 bends + kicker Wall 3/21/2012 Y. Nosochkov

LTU wall: alternate lattice End of wall No magnets Wall Magnets are placed outside of the wall interference region. 3/21/2012 Y. Nosochkov

LTU parameters Original Alternate LTU HXR + SXR quads 48 LTU HXR + SXR main bends 10 8 LTU HXR R56 (mm) 0.385 LTU SXR R56 (mm) 0.193 1.004 LTU HXR I5 1.1e-9 3.0e-9 LTU SXR I5 2.2e-9 4.1e-9 LTU region is from muon wall to HSSSTART/SSSSTART. Tunable R56 in the original 4-bend arc. Non-tunable R56 in the 2-bend arc  Tuning could be achieved with an additional tuning chicane. DgeISR = 4∙10-8 ∙ I5 ∙ E6 = 0.002 mm-rad at I5 = 4.1e-9 and 15 GeV 3/21/2012 Y. Nosochkov

Chicane option for R56 tuning LB LBB J Example: LBB = 2 m, LB = 1.5 m, DR56 = -1.004 mm  J = 12.94 mrad, B = 4.31 kG at 15 GeV 3/21/2012 Y. Nosochkov

Back-up slides 3/21/2012 Y. Nosochkov

Un-normalized beam X-phase space at LTUS wires 3/21/2012 Y. Nosochkov