S. Fartoukh1st General HL-LHC meeting, 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 & (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)

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, Limit from the “non-triplet” side of the machine Limit from the triplet (critical field) Ref: SLHCPR0038

Motivations (2/2)  Bare minimum  *  30 cm found for the former upgrade project (Phase I) with a 120 T/m mm NbTi triplet.  3 options to reach the HL-LHC  * of 15cm (or below) 1)480 T/m 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,

S. Fartoukh 1st General HL-LHC meeting, What would happen for a “standard squeeze” to  * =30 cm (120 T/m triplet) ? Sextupole powering scheme and gradients (beam1) vs.  *  *=1.5 m 550A - 550A  *=30 cm  550A!  *=30 cm Q5/Q6 close to 0! Matching section (MS) 160 T/m

S. Fartoukh1st General HL-LHC meeting,  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 beta’s 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 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

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, S. Fartoukh

1st General HL-LHC meeting,  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

S. Fartoukh1st General HL-LHC meeting,  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

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 SF’s  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, S. Fartoukh

1st General HL-LHC meeting, 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 (+/ window) IP3IP7 IP5IP1 2) Correction of the spurious dispersion induced by the X-angles in IR1 and IR5

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, /afs/cern.ch/eng/lhc/optics/ATS_V6.503

S. Fartoukh1st General HL-LHC meeting, 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!

S. Fartoukh1st General HL-LHC meeting, 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) (30/30 cm) (7.5/30cm ↔30/7.5cm in IR1↔IR5)3635

S. Fartoukh1st General HL-LHC meeting, 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<0) 25% octupole (K<0) 37.5% octupole (K<0)

ATS MD results over 2011 (1/3)  A full program deployed over 2011: a total of 8h for HW tests w/o beam + 23h with beam. 1.May: ATS injection optics and ramp (new integer tunes, arc and IR optics).  successful 2.July: Pre-squeezed optics to  * =1.2 m in IR1 and IR5, and telescopic squeeze demonstrated only for IR1, reaching  * = 30 cm.  successful 3.November: Pre-squeezed optics to  * =40 cm in IR1 and IR5, and squeeze of IR1 and IR5 down to  * = 10 cm.  Pre-squeeze successful, beam lost preparing for the squeeze (misunderstanding with tune knob manipulation) S. Fartoukh1st General HL-LHC meeting,

Beam1 captured and circulating at the first injection! (MD of May) 1st General HL-LHC meeting, … starting from nominal injection pre-settings, which means that the CO correction of the nominal optics is already very local. 30 min. later: 0.15 mm r.m.s. closed orbit (crossing knobs off) S. Fartoukh Thanks to J. Wenninger et al.

1st General HL-LHC meeting, New settings for the damper (phases) and <50 turns damping time at the first attempt First dump test … What is what, the beam or the target? A series of tests at 450 GeV: damper, dump, RF trims … S. Fartoukh Thanks to W. Hofle et al. Thanks to B. Goddard et al.

1st General HL-LHC meeting, … The ramp: excellent life time, transmission of intensity, and no emittance growth S. Fartoukh

1st General HL-LHC meeting, Telescopic principle (×4) demonstrated for IR1 (MD of July) Thanks to the OP group for the excellent preparation: M. Lamont, G. Mueller, L. Ponce, S. Redaelli, J. Wenninger et al.

1st General HL-LHC meeting,  15-20% level reached for the  -beating after one single correction iteration Pre-squeeze pushed to 40 cm in IR1 & IR5 (MD of Nov.) Qx(  ) at  * =40 cm Qy(  ) at  * =40 cm  No (small) Q’’, Q’’’ … Thanks to the OMC team: R. Miyamoto, R. Tomas, G. Vanbavinckhove et al. S. Fartoukh

1st General HL-LHC meeting, Conclusions & Outlooks  The full ATS scheme will be hopefully demonstrated next year with 10 cm   reached both at IP1 and IP5 and chromatically corrected.  However the LHC was NOT designed for the ATS. It is a global scheme and some important questions need to be answered (e.g. cross-talks with the long term Physics program of Alice & LHCb).  Betting on the success, the HL-LHC will profit from the ATS in order to reduce   below ~ 25/30 cm (with Nb 3 Sn/NbTi), but provided an IT aperture larger than 120 mm (found optimal for the former upgrade optics scheme).  With “no (or very far)   limit” with the ATS, my recommendation for the new IT would be - aperture first (≥150 mm) with a “reasonable gradient” (≥ 100T/m) -…which for Nb 3 Sn would mean a target of 180 mm – 120 T/m ??