Slide 1

S. Fartoukh1st General HL-LHC meeting, 17.11.2011 1 The Achromatic Telescopic Squeeze (ATS) S. Fartoukh CERN/BE-ABP Motivations Basic principles of the ATS scheme Limitations & by-products, open questions & unknown territories ATS MD results over 2011 Conclusions Main References: S. Fartoukh, sLHC-PR0038 & sLHC-PR0049/0053: LHC Optics limitations(2010) & description of the ATS scheme (2010) R. de Maria, S. Fartoukh, sLHC-PR0050: Optics analysis and Tracking results with ATS optics (2010) S. Fartoukh et al., ATS Note 2011-033 & 2011-060 (MD results) Optics & Layout :/afs/cern.ch/eng/lhc/optics/SLHCV3.0 (S. Fartoukh, ATS optics & layout with a 120 T/m triplet, completed) /afs/cern.ch/eng/lhc/optics/SLHCV3.1 (R. de Maria, ATS optics & layout with a 150 T/m triplet, under construction) /afs/cern.ch/eng/lhc/optics/ATS_V6.503 (S. Fartoukh, ATS optics & layout with the 200 T/m existing triplet under test in the LHC) Slide 2 Motivations (1/2) Severe optics limitations found in the LHC, regardless of the available aperture! optics matchability to the arcs (some IR quads going to 0, others to max. field). correct-ability of the chromatic aberrations (arc sextupole strength). This limits the max. possible IT which can be produced in the triplet (IT), corresponding to an optimal IT aperture (not technology dependant) and to a min. possible * S. Fartoukh1st General HL-LHC meeting, 17.11.2011 2 Limit from the non-triplet side of the machine Limit from the triplet (critical field) Ref: SLHCPR0038 Slide 3 Motivations (2/2) Bare minimum * 30 cm found for the former upgrade project (Phase I) with a 120 T/m - 120 mm NbTi triplet. 3 options to reach the HL-LHC * of 15cm (or below) 1)480 T/m - 120 mm ultra-short triplet (~ 40 T critical field) Not for this Project! 2)Heavy surgery in the ring: a) double (triple?) the length of the low-beta insertions, eating in the arcs and with more matching standalone quadrupoles to solve the optics matchability limit. b) profit from above to find a local chromatic correction scheme for the triplet (if possible?), or equip ~500 arc quadrupoles with twice stronger chromatic sextupoles. Hardly fit within the planning/budget! 3)Look for non-classical and new concepts The ATS scheme which does the above surgery (almost) for free! S. Fartoukh1st General HL-LHC meeting, 17.11.2011 3 Slide 4 S. Fartoukh 1st General HL-LHC meeting, 17.11.2011 4 What would happen for a standard squeeze to * =30 cm (120 T/m triplet) ? Sextupole powering scheme and gradients (beam1) vs. * Transition @ *=1.5 m 550A - 550A *=30 cm 550A! *=30 cm Q5/Q6 close to 0! Matching section (MS) 160 T/m Slide 5 S. Fartoukh1st General HL-LHC meeting, 17.11.2011 5 All the ingredients already available to blow-up the s in the arcs at 7 TeV! 1) Huge aperture margin in the arcs at 7 TeV given by the large dynamic energy range of the machine: ~ factor 16 margin to increase the betas in the arcs at 7 TeV. 2) Presently, about 150 quadrupole knobs moderately used (IR2/IR8) or not used at all (IR4/IR6) in pp collision @7 TeV why not using them for squeezing IR1 and IR5? The ATS: first idea to implementation(1/2) Optics limitations with corresponding min. * Cure Optics flexibility (very low gradient reached for Q5/Q6, max. gradient in Q7 and QT12/13) *_min ~ 20 cm (for NbTi) Change the matching conditions at the IR boundaries Blow-up the functions in the arcs 81/12/45/56 Sextupole strength for the correction of the chromatic aberrations (Q but also off- momentum -beat, Q,..) *_min ~ 30 cm (for NbTi) Increase the sextupole efficiency at constant field Blow-up the functions in the arcs 81/12/45/56 Slide 6 The ATS: first idea to implementation (2/2) A squeeze procedure in 2 steps 1) An almost standard squeeze, the Pre-squeeze, acting on the matching quads of IR1 and IR5, till reaching some limits (sextupoles, matching section). 2) A continuation of the squeeze, called Squeeze, acting on IR2/8 for squeezing IR1 and IR4/6 for IR5, with -beating bumps induced in the arcs 81/12/45/56 to boost the sextupole efficiency. With additional features to warrant the correction of the chromatic aberrations (Q, Q, off-momentum -beat, spurious dispersion). 1st General HL-LHC meeting, 17.11.2011 6S. Fartoukh Slide 7 1st General HL-LHC meeting, 17.11.2011 7 arc increased by a factor of 4 in s45/56/81/12 starting from a relaxed pre-squeezed optics at * =60 cm Squeezed optics (round): * = 15 cm in IR1 and IR5 (120 T/m IT) /afs/cern.ch/eng/lhc/optics/SLHCV3.0 Slide 8 S. Fartoukh1st General HL-LHC meeting, 17.11.2011 8 arc increased by a factor of 2 or 8 in s45/56/81/12 depending on the * aspect ratio in IP1 and IP5 Squeezed optics (flat): * x/y = 7.5/30 cm alternated in IR1 and IR5 (120 T/m IT) /afs/cern.ch/eng/lhc/optics/SLHCV3.0 Slide 9 Why does it work?.. Zoom in from IP4 to IP5 for the flat optics (beam1) y between the 12 strong SD sextupoles y (Q11 IP ) = 1.25 y with y ~ 1/2 tan -1 ( min / max ) arc * ) V cst x between the 9 strong SFs one missing at Q10 to complete 5 -pairs x (Q14 IP ) = 1.25 x with x ~ - 1/2 tan -1 ( min / max ) arc * ) H cst 1st General HL-LHC meeting, 17.11.2011 9S. Fartoukh Slide 10 1st General HL-LHC meeting, 17.11.2011 10 Montague functions (W=1000 =100% at =0.001) Then a series of fundamental chromatic properties (examples for 8228 optics) 1) Chromatic correction using only one sector of sextupoles per IT Up to 10m H or V spurious dispersion induced in the IT (~20 mm coil_ID) Dispersion reduced to ~50cm in the IT (contribution from IR2 and IR8) thanks to 2.5 mm orbit bumps induced in sectors 81/12/45/56 Closed orbit with X-scheme in IR8/IR1/IR2 and IR5 H and V dispersion Tune vs. p (+/- 0.0015 window) IP3IP7 IP5IP1 2) Correction of the spurious dispersion induced by the X-angles in IR1 and IR5 Slide 11 11 Beam size [mm] and dispersion at 3.5 TeV (for =3.5 m) Tunes vs. p Montague functions Triplet aperture (compared to 4 sigma's (X-angle OFF) Reaching * =10 cm in the existing LHC at IP1&IP5 (200 T/m IT) S. Fartoukh1st General HL-LHC meeting, 17.11.2011 /afs/cern.ch/eng/lhc/optics/ATS_V6.503 Slide 12 S. Fartoukh1st General HL-LHC meeting, 17.11.2011 12 Limitations, by-products, unknown (1/3) A non-exhaustive list of topics being or to be addressed Dynamic aperture reduction from big s in the arcs (w/o talking about the triplet). Mitigation measures: 1)Push the pre-squeezed * ( 25% from Nb3Sn triplet, 20% possible from additional sextupoles in the dispersion suppressor and 10% higher current, other idea?). 2)Study global non-linear correctors (one outstanding out-layer is the systematic geometric b6 of the main quadrupoles). Impact on Operation, Physics Program, collimation,.. 1)Impact of changing the optics in IR4 (RF & beam instrumentation) and IR6 (dump insertion) during the squeeze sometimes beneficial, sometimes not. 2)Cross-talks between the ATS and any eventual squeeze of IR2 (Alice, LHeC) & IR8 (LHCb) not analyzed in details. 3)IR collimation, in particular installation of cryo-collimators at Q8 & Q10 in IR1/5 Is it compatible with the ATS?.. The normalized dispersion and betatron phases change a lot with the ATS! Slide 13 S. Fartoukh1st General HL-LHC meeting, 17.11.2011 13 Limitations, by-products, unknown (2/3) Maximum * lever arm offered by IR2, IR8, IR4 and IR6 44 round (yes), 82 or 28 flat (yes), 88 round (partly yes), or even more?? IBS vs. optics (for some set of LHC parameters N b =1.7E11, ,V= 3.75 m, L =1.6 eV.s, i.e. z = 6 cm): Courtesy of A. Vivoli We loose in the H plane and gain in the Z plane. Can we gain in both planes, e.g. mismatching also the dispersion with the ATS? Machine impedance and Landau damping: arc increased by up to 100% (for an 88 round optics) impact on the imaginary tune shift and therefore the instability rise time but Landau damping (MO) efficiency increased by 10 even 20! Exemple of Optics (starting from a pre-squeezed optics at 60 cm) Tx (h)Tz (h) 1111 (60/60 cm)4929 2222 (30/30 cm)4431 8228 (7.5/30cm 30/7.5cm in IR1IR5)3635 Slide 14 S. Fartoukh1st General HL-LHC meeting, 17.11.2011 14 Limitations, by-products, unknown (2/3) Landau octupoles of the arcs as foot-print shaper: The ATS-LHC becomes the first high energy machine where non-linear correctors are efficient enough to shape the head-on bb tune spread. Do we gain more than what we may loose: e.g. zero dynamic aperture (4 th order resonances, folding), huge Q from octupoles in the arcs,?? 0% octupole 12.5% octupole (K