Towards an extremely-flat beam optics with large crossing angle for the LHC

Towards an extremely-flat beam optics with large crossing angle for the LHC

José L. Abelleira, PhD candidate EPFL, CERN Beams dep. Supervised by F. Zimmermann, CERN Beams dep.

Thanks to: S. Fartoukh, S.Russenschuck (CERN), D.Shatilov (BINP SB RAS,Novosibirsk), R. Tomas (CERN), C. Milardi, M. Zobov (INFN/LNF, Frascati (Roma))

Warsaw, 25th April 2012

Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Contents

• Flat beam optics. Comparison.• Double half-quadrupole• Large Piwinski angle & crab-waist collisions• Luminosity• Future work, open questions• Conclusions


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Flat beam optics

Peak luminosity

To increase luminosity:-Reduce both σx

* and σ y*

-Substantially reduce σy*

Δμx Δμy

sext1sext2sext3

π/23π/2π/2

ππ/2

5π/2

FfnNLyx

b**

2

4 Local chromatic correction in Y.

First time ever for LHC!

sext1 sext2 sext3

Chromatic correction

βx*=1.5 m

βy*=1.5 cm

βx*βy

*=15cmx15cm (nominal ATS optics with crab cavities)

Crab –waist collisions


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45 mm

Large crossing angle-> large Piwinski anglex

z

2

15σy

15σx

σx/ σy=10 Minimum required according to beam-beam simulations.

2 mrad

Reference orbit


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Actual LHC optics

IPThe 2 beams see opposite gradients

+ +


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Flat beam LHC optics

IP

The 2 beams see the same gradients

- + - +How to produce opposite

gradient in the same pipe?


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Double half-quad

-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08-0.08

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B0=-5.8 T g=115 T/m

NbTi

S.Russenschuck


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Kick due to the dipolar term


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Matching

Arc (MQ11)Arc (MQ11)

βx=127 mβy=21 mDx=1.5 m

βx=20 m βy=207 mDx=0.6 m

DSMSFF

Separation bending magnets


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Large Piwinski angle

Luminosity reduction through F but…1-Decrease overlapping area. Lower βy decrease

;y

yNL

;1 2

yx

yy

N;)1( 2

x

xN

x

z

2

Head-on or small φ

zCS

Large Piwinski angle

xCS2

Hourglass effect limits βy decrease CSy

cmx 12

!

2-More particles N for the same beam-beam tune shift3-It opens the possibility for crab-waist collisions

Collision section (CS)


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Crab-waist collisions

Normal collision scheme

Crab-waist collision scheme

With Large Piwinski Angle Collision Point ≠ Interaction Point P.Raimondi,

D.Shatilov, M. Zobov


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Crab-waist collisions

Conditions

)12(2

n

m

y

x

yy

xxskl

*

* /Sextupole strength

In particular25

y

x

mlmk

s 80313.0 3

2

2

2

202

y

x

P.Raimondi, D.Shatilov, M. Zobov


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Crab-waist simulationsResonance suppression

CW = 0

CW = 0.5

Dmitry Shatilov Mikhail Zobov


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Luminosity gainNx10 11\εn(μm)

3.75 3.5 3 2.5 2.21.15 0.6262 0.6721 0.7868 0.947 1.07761.5

1.0653 1.1435 1.3387 1.6111 1.83342 1.8939 2.0328 2.3798 2.8642 3.2594

2.52.9592 3.1763 3.7185 4.4753 5.0928

34.2613 4.5738 5.3546 6.4444 7.3336

Luminosity (1034 cm-1s-1 )

Nx10 11\εn(μm)3.75 3.5 3 2.5 2.2

1.151.1991 1.2938 1.5294 1.8563 2.1217

1.5 2.04 2.2012 2.602 3.1581 3.60972

3.6266 3.9132 4.6257 5.6144 6.41732.5

5.6666 6.1143 7.2276 8.7725 10.0273

8.16 8.8046 10.4078 12.6324 14.4389

Main limitation: the crossing angle due to the separation of the double half quadFurther improvements in the double half-quad. design can reduce the crossing angle (Nb3Sn)

mrad4

mrad2

θ/2= 2 mradθ/2=1 mrad


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Flat emittance

Limitation: aperture of the half quadSolution: reduce εy keeping constant εx εy

ε βhqεσ hq σ hq βy

*εx

εyβhq

Squeeze of the emittance ellipse

βy increase in the half-quad.->reduction on σy*= sqrt(εy βy

*)

βx decrease in the half-quad.->reduction of horizontal chromatic aberrations-> increase on σx

*= sqrt(εx βx*)

->Geometric reduction factor increased F=(1+ (ϴ/2)σz /σx)-1/2

Luminosity increase through significant σy* reduction and F increase


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Flat emittance

Luminosity

Keep εxεy constant and vary εx/εy

Θ=4 mrad N=2x1011


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Work in the next months

– Study of the aberrations– Rematch the dispersion– Improvement of the half-quad– Dynamic aperture– Beam-beam simulations


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Open questions

– Field quality of the double half-quad & correction scheme– Dispersion matching for the chromatic correction– 2nd order dispersion cancellation


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Conclusions• An extremely-flat beam optics (βy

*/βy*=100) is conceptual possible

for LHC– Large Piwinski angle, to reduce the collision area and allow for a

lower βy decrease– Local vertical chromatic correction– Possibility to have crab waist collisions that can increase

luminosity and suppress resonances– Can accept higher brightness.

• The performance of the new optics can be improved– Future half-quad designs (Nb3Sn)– Using a flat emittance– HE-LHC? Already flat emittance due to SR


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Thank you…

…For your attention

Towards an extremely-flat beam optics with large crossing angle for the LHC

Documents

large crossing angle

beambeam simulations

contentsflat beam optics

beambeam tune shift3

lhc jos

15cmx15cm nominal ats

lower y

cern beams