Pushing the LHC nominal luminosity with flat beams Beam aspect ratio at the IP versus triplet aperture Pushing the luminosity by 10-20% Extrapolating the gain to the LHC upgrade Open issues and future plans S. Fartoukh, ABP-RLC meeting, 28-10-2005

Luminosity with flat beams Flat beam means The Xing plane is always the plane where the beam size is the largest at the IP (i.e. the smallest in the triplet) To gain aperture in the triplet (smaller X-angle requested and better matching between beam-screen and beam aspect ratio, see next slide) To gain in luminosity (geometric loss factor closer to unity)   Luminosity calculated for two head-on colliding round beams r.m.s. bunch length (7.5 cm in collision for the nominal LHC) Full X-angle in s units (9.5 s for the nominal LHC) S. Fartoukh, ABP-RLC meeting, 28-10-2005

Beam aspect ratio vs triplet aperture (1/5) Beam screen orientation for H/V scheme In both cases, H-separation of about 9.5*max(sx,b1 ,sx,b2) Effect of decreasing the beam aspect ratio at the IP (and increasing the vert. X-angle) In both cases, V-separation of about 9.5*max(sy,b1 ,sy,b2) Effect of increasing the beam aspect ratio at the IP (and decreasing the vert. X-angle) Find the optimum matching between beam-screen and beam aspect ratio S. Fartoukh, ABP-RLC meeting, 28-10-2005

Beam aspect ratio vs triplet aperture (2/5) Nominal LHC (b* = 55 cm, round beam r = 1) ymax~ 6.5 mm Beam1 in IR1 bx,max~ 4.5 km by,max~ 4.5 km Beam2 In IR1 Vertical crossing a = 285 mrad n1 ~ 7 (aperture spec. of Q2 still to be finalised) Round beam r = 1 bx* = by* = 55 cm S. Fartoukh, ABP-RLC meeting, 28-10-2005

Beam aspect ratio vs triplet aperture (3/4) Flat beam with r = 2 (i.e. bx* = 110 cm and by* = 27.5 cm) ymax~ 5 mm Beam1 in IR1 bx,max~ 2.5 km by,max~ 8.0 km Beam2 in IR1 Flat beam r = 2 bx* = 110 cm, by* = 27.5 cm Horizontal crossing a = 285/r1/2 = 201 mrad n1 ~ 7 (even slightly better than the nominal case) S. Fartoukh, ABP-RLC meeting, 28-10-2005

Beam aspect ratio vs triplet aperture (4/5) Optimum reached for r ~ 1.6 ymax~ 5.5 mm Beam1 in IR1 bx,max~ 3.0 km by,max~ 7.0 km Beam2 in IR1 Flat beam r = 1.6 bx* = 88 cm, by* = 34.4 cm Horizontal crossing a = 285/r1/2 = 225mrad n1 ~ 7.5! S. Fartoukh, ABP-RLC meeting, 28-10-2005

Beam aspect ratio vs triplet aperture (5/5) Reducing further by* by 15% keeping constant bx* ymax~ 5.5 mm Beam1 in IR1 bx,max~ 3.0 km by,max~ 8.0 km Beam2 in IR1 Flat beam bx* = 88 cm, by* = 30 cm Horizontal crossing = 225mrad (unchanged w.r.t. previous case) n1 ~ 7 S. Fartoukh, ABP-RLC meeting, 28-10-2005

Pushing the luminosity by 10-20% Case bx* [cm] by* [cm] a *[mrad] n1 in the triplet Geometric loss factor [%] L/Lnom Nominal r=1.0, b*=55cm 55.00 285 ~7 83.9 1.00 Flat r=2.0, b*=55cm 110.00 27.50 201 95.1 1.13 r=1.6, b*=55cm 88.00 34.37 225 ~7.5 92.7 1.10 r~1.7, b*~51cm 30.00 1.18 All these cases being allowed by the nominal LHC hardware:layout, power supply, optics antisymmetry, b.s. orientation in the triplets (only changing the present H/V scheme into V/H scheme)! S. Fartoukh, ABP-RLC meeting, 28-10-2005

Extrapolating the gain to the LHC upgrade Rather than using crab-cavities or so-called “D0” (orbit corrector very closed to the IP), or decreasing the bunch length. Using flat beam is an “hardware-free” alternative to largely increase the geom. luminosity loss factor for b* = 25cm: 57% for a round beam  81/75% for a flat beam with r=2/1.6 2) to gain about 10% of aperture in the triplet with (almost) no loss of luminosity, i.e. reduce by 10% the peak coil field. S. Fartoukh, ABP-RLC meeting, 28-10-2005

Open issues and future plans (1/2) Chromatic correction:  Q’ correction is a non-issue with the actual LHC sextupole scheme: SF, resp. SD, pushed to 36%, resp. 62%, of nominal field even in the worst case of H-H, resp. V-V, scheme (in any case not allowed by actual b.s. orientation in IR1 and IR5)  Q’’ and off-momentum beta-beat correction  should be OK (as a first guess based on previous study: S.F., LPR 308)  But still to be checked (IR phasing can only partially help for the H/V scheme) S. Fartoukh, ABP-RLC meeting, 28-10-2005

Open issues and future plans (2/2) Beam-beam:  Parasitic b-b compensation is only partially granted by the H/V scheme with flat beam: for r < 2.4 still better than H-H or V-V scheme with round beams for r ~ 1.6, similar to the case of only one working low-beta insertion (scenario that has to be envisaged in any case)  Head-on tune shift independent r for H/V scheme: Thin lens optics for H/H, V/V, H/V scheme with flat beams still to be done for robust b-b studies (tune foot-print, DA …) S. Fartoukh, ABP-RLC meeting, 28-10-2005