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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, 25 th April 2012

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Contents Flat beam optics. Comparison. Double half-quadrupole Large Piwinski angle & crab-waist collisions Luminosity Future work, open questions Conclusions 2 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Flat beam optics Peak luminosity To increase luminosity: -Reduce both σ x * and σ y * -Substantially reduce σ y * ΔμxΔμx ΔμyΔμy sext1 sext2 sext3 π/2 3π/2 π/2 π 5π/2 Local chromatic correction in Y. First time ever for LHC! sext1 sext2 sext3 Chromatic correction β x * =1.5 m β y * =1.5 cm β x * β y * =15cmx15cm (nominal ATS optics with crab cavities) Crab –waist collisions 3 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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45 mm Large crossing angle-> large Piwinski angle 15σ y 15σ x σ x/ σ y =10 Minimum required according to beam-beam simulations. 2 mrad Reference orbit 4 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Actual LHC optics IP The 2 beams see opposite gradients + 5 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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

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Double half-quad B 0 =-5.8 T g=115 T/m NbTi S.Russenschuck 7 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Kick due to the dipolar term 8 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Matching Arc (MQ11) β x =127 m β y =21 m D x =1.5 m β x =20 m β y =207 m D x =0.6 m DSMSFF Separation bending magnets 9 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Large Piwinski angle Luminosity reduction through F but… 1-Decrease overlapping area. Lower β y decrease Head-on or small φLarge Piwinski angle Hourglass effect limits β y decrease ! 2-More particles N for the same beam-beam tune shift 3-It opens the possibility for crab-waist collisions Collision section (CS) 10 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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

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Crab-waist collisions Conditions Sextupole strength In particular 12 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC. P.Raimondi, D.Shatilov, M. Zobov

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Crab-waist simulations Resonance suppression CW = 0 CW = 0.5 Dmitry Shatilov Mikhail Zobov 13 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Luminosity gain Nx10 11 \ε n (μm) Luminosity (10 34 cm -1 s -1 ) Nx10 11 \ε n (μm) Main limitation: the crossing angle due to the separation of the double half quad Further improvements in the double half-quad. design can reduce the crossing angle (Nb 3 Sn) θ/2= 2 mrad θ/2=1 mrad 14 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Flat emittance Limitation: aperture of the half quad Solution: reduce ε y keeping constant ε x ε y ε β hq ε σ hq βy*βy* εxεx εyεy β hq Squeeze of the emittance ellipse β y increase in the half-quad.->reduction on σ y * = sqrt(ε y β y * ) β x decrease in the half-quad.->reduction of horizontal chromatic aberrations -> increase on σ x * = sqrt(ε x β x * ) ->Geometric reduction factor increased F=(1+ (ϴ/2)σ z /σ x ) -1/2 Luminosity increase through significant σ y * reduction and F increase 15 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Flat emittance Luminosity Keep ε x ε y constant and vary ε x/ ε y Θ=4 mrad N=2x Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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

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Open questions – Field quality of the double half-quad & correction scheme – Dispersion matching for the chromatic correction – 2 nd order dispersion cancellation 18 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Conclusions An extremely-flat beam optics (β y * /β y * =100) is conceptual possible for LHC – Large Piwinski angle, to reduce the collision area and allow for a lower β y 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 (Nb 3 Sn) – Using a flat emittance – HE-LHC? Already flat emittance due to SR 19 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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Thank you… …For your attention 20 Jose L. Abelleira. Towards an extremely-flat beam optics with large crossing angle for the LHC.

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