Alternate Lattice for LCLS-II LTU

Y. Nosochkov

LCLS-II Physics Meeting, March 21, 2012

Y. Nosochkov 2

Goals

3/21/2012

• 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

Y. Nosochkov 3

Original lattice

3/21/2012

L0

L1 L2 L3HXR

SXR

µ

BC2BC1

gun

DL1 DL211-3 to 14-4 14-7 to 20-4

11-1

sd

sd sdsd

sd

sd

sd

sdsz sz

sz

LTU

BypassLinac

Undulator

HXR

Y. Nosochkov 4

SXR3 wires,4 collimators

-1.2o

Septum

Original LTU

3/21/2012

HXR2.4o 4-bend 4 wires, 4 collimators

45o FODO

2.4o 4-bend 1.2o

Y. Nosochkov 5

Original vertical separation scheme

3/21/2012

Kicker strength = 0.07 kGm at 15 GeV P. Emma

Y. Nosochkov 6

Lambertson septum in the original scheme

3/21/2012P. Emma

Y. Nosochkov 7

Kicker vertical dispersion is not canceled

3/21/2012

Y-orbit bump Y-dispersion in the LTUS

Y-dispersion in LTUS through dump

Y. Nosochkov 8

Canceling the kicker dispersion

3/21/2012

• 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).

Large orbit when Y-dispersion is canceled with 2 kickers and 3 DC bends

sept

um

• 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.

Y. Nosochkov 9

septum

2.4o 2-bend 1.2o 2-bend

X-kicker DC1 DC2

3/21/2012

• 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.

AlternateSXR LTU

OriginalSXR LTU

septum

2.4o 4-bend 1.2o 2-bend

Y-kicker DC1 DC2

Kicker strength = 0.17 kGm at 15 GeV and Dx=-10mm

Long drift to minimize wall interference

Long drift to maximize HXR/SXR separation

Low bx at bends

Y. Nosochkov 10

sept

um

kick

er

QD

L44

BX42

QD

L45

QD

L46

QD

L43

X = -10 mm at septumOff-axis through QDL44,45,46 and BX42

Kicker orbit

3/21/2012

Y. Nosochkov 11

First look at the current sheet septum design for horizontal separation (C. Spencer)

3/21/2012

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.

SXR HXR

Y. Nosochkov 12

Geometry: original 4-bend arc versus alternate 2-bend arc

3/21/2012

19.6

cm

Wall

Original: some magnets interfere with the wallAlternate: only beam pipe interferes with the wall

Y. Nosochkov 13

SXR diagnostic and 2nd dogleg bend pair

3/21/2012

Original 120o b-waist diagnostic

w

wwcx,cy cx,cy

triplets

90o FODO diagnostic

2x90o FODO

wwwwcy cx cy cx

Alternate

Y. Nosochkov 14

Wire-1

Wire-2

Wire-3

Wire

-4

Normalized beam X-phase space at LTUS wires

3/21/2012

Wire phase separation:mx : 65°-25°-65°bx= 14 max= ±1.43

xx

x

xx

n

n

Y. Nosochkov 15

Normalized beam Y-phase space at LTUS wires

3/21/2012

Wire-1

Wire-2

Wire

-3W

ire-4

Wire phase separation:my : 25°-65°-25°by= 14 may= ±1.43

Y. Nosochkov 16

SXR dogleg geometry: original versus alternate

3/21/2012

19.3

cm

Y. Nosochkov 17

HXR2.4°

45° FODO diagnostic

SXR

Septum

2.4° 1.2°-1.2°

90° FODO diagnostic

Complete alternate LTU lattice

3/21/2012

Y. Nosochkov 18

Complete alternate LTU geometry

3/21/2012

sept

um

Pano

fsky

Pano

fsky

Red -- bends, blue -- quads, green -- x-kicker, septum, DC bend

V-bend

1st Panofsky quadseparation: 237 mm

HXR

SXR

Pano

fsky

Downstream of the LTU the HXR/SXR geometry is matched to the original geometry

Y. Nosochkov 19

LTU wall: original lattice

3/21/2012

Interference: 3 quads + 2 bends + kicker

Wall

Y. Nosochkov 20

LTU wall: alternate lattice

3/21/2012

Magnets are placed outside of the wall interference region.

End ofwallNo magnets

Wall

Y. Nosochkov 21

LTU parameters

3/21/2012

Original Alternate

LTU HXR + SXR quads 48 48

LTU HXR + SXR main bends 10 8

LTU HXR R56 (mm) 0 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 E∙ ∙ 6 = 0.002 mm-rad at I5 = 4.1e-9 and 15 GeV

Y. Nosochkov 22

Chicane option for R56 tuning

3/21/2012

LB LBB

J

)32

(2 256 BBB LLR J

Example: LBB = 2 m, LB = 1.5 m, DR56 = -1.004 mm

J = 12.94 mrad, B = 4.31 kG at 15 GeV

Y. Nosochkov 23

Back-up slides

3/21/2012

Y. Nosochkov 24

Un-normalized beam X-phase space at LTUS wires

3/21/2012