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

2. 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

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

4. 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

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

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. 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

18. 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

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

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

21. 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 = mm-rad at I5 = 4.1e-9 and 15 GeV
3/21/2012
Y. Nosochkov

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

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

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