A new overall LHC optics for the LHC IR upgrade Phase I From new concepts LIUWG

1
A new overall LHC optics for the LHC IR upgrade
Phase I From new concepts (LIUWG15, May 2008)
to a complete solutionS. Fartoukh for the ABP
Upgrade Team 26/03/2009

• Chromatic aberrations at low b, needs and
  principles for its correction.
• SLHCV1.0 a new overall LHC optics with several
  changes w.r.t. V6.503 and very attractive
  chromatic properties.
• Detailed layout and optics of IR1 IR5
• Available tools
• On-going dedicated studies, preliminary results
  and future plans
• - Basic optics checks, overall aperture at
  injection, matching section and triplet aperture
  in collision.
• - Closed orbit correctability
• - Squeeze
• - Dynamic aperture _at_450 TeV 7 TeV, beam-beam
• Conclusions

S. Fartoukh, LIUWG 26/03/2009
2
Chromatic aberrations at low b (1/3)

• Off-momentum b-beating, NL chromaticity Q and
  Q
• Strategy for V6.503 (IR1 5 with b 55 cm)
• Passive compensation between IR15 by p/2
  betatron phasing between IP1 IP5.
• Off-momentum b-beating bump between IR1 and IR5
  reaching 40 _at_ d0.001.
• Probably OK for collimation (R. Assmann, LIUWG4)
  but the beam will tell.
• If same strategy applied for Phase I (IR1 5
  with b 25 cm)
• Linear off-mom. b-beat minimized in IR7 but
  reaching 100 _at_ d0.001 in IR3
• Q easily corrected to 2 units 44 - 74 of
  Imax (550A) needed in SF-SD.
• No Q, but huge Q which is the indication
  of large non-linear off-momentum b-beat (the
  phase advance from IP1 to IP5 is no longer p/2
  for non-zero d).
• See illustrations in next slides (coming from
  LIUWG15 presentation)

S. Fartoukh, LIUWG 26/03/2009
3
V6.503 but in IR1 5 with b 25cm and new IT
(see LIUWG15)
W 1000 in IR3
W 0 in IR7 and in the new triplets
Min. momentum window d 10-3
Mon. collimator d 1.510-3
IP3
IP1
IP5
IP7
IP1
Bucket d 0.3610-3
Linear Montague function Wx,y (s)
?b/?d (s)/b(s)amp.
Tune v.s. d Qx,y (d)

• Beam life time and background to the experiments
  when moving d by a few 10-4 , e.g. for dispersion
  or chromaticity measurement??
• Where the diffracted protons escaping IR3 (i.e.
  with dlt a few permil) will be lost?? For them the
  off-momentum b-beating is maximum on the other
  half of the machine, in particular IR7 and the
  new ITs!!
• The scheme easily breaks down when the optics is
  not strictly the same in IR1 and IR5!!
• How big is the non-linear off-mom. b-beating in
  the new ITs and IR7??.. See next slide.

S. Fartoukh, LIUWG 26/03/2009
4

• Db(d)/b(0)
• in the triplet of IR1
• Lin. term corrected
• ? Large sec. order

• Db(d)/b(0)
• in the triplet of IR5
• Lin. term corrected
• ? Large sec. order

Off-momentum Triplet aperture!

• Db(d)/b(0) in IP7
• Lin. term corrected
• Higher order effects (much bigger at some TCP)

• Db(d)/b(0) in IP3
• Lin. term not corrected
• ? Large sec. order

Collimation efficiency, even after phasing IP1
and IP5?

• ..Well, is it reasonable to bet on an increase of
  the intensity for Phase I/II if the
• overall LHC linear optics is no longer be
  controllable above d 2-3 10-4 in collision !?

S. Fartoukh, LIUWG 26/03/2009
5
Chromatic aberrations at low b (2/3)

• Spurious H/V dispersion from the X-schemes in IR1
  5
• Can reach 6 m for worst phase advances between
  IR1 5, i.e. 12 mm coil ID lost!
• Dx/y can easily reached 0.5-1 m in the TCP/TCS of
  IR7.. Collimation efficiency!
• Correctable in the H-plane (IR5) via
  IR-rematching but no IR knobs for Dy!
• H V arc orbit bumps tested in the past w/o
  success not enough MCB strength, huge orbit in
  the arcs ( e.g. P. Leunissen 1999) because
  decoherence of the dispersive wave in the arcs
  (arc cell phase too far from 90 degrees) and also
  and mainly not the right phase between triplet
  and mid-arc!!

V6.503 but in IR1 5 with b25 cm and new IT
(see LIUWG15)
IP1
IP1
IP5

• With X-scheme
• 5 - 6 m in MQX (beam1-2)
• substantially modified in IR3/7

Dxy(s) w/o X-scheme (arc-regular from Q13 to
Q13 and matched to zero in IP1,2,5 8)
H-dispersion generated on purpose in IR3
S. Fartoukh, LIUWG 26/03/2009
6
Chromatic aberrations at low b (3/3)

• What to do?
• Revisit the conceptual optics of the LHC arcs
• Was driven by imposing a strong decoherence of
  the linear and non-linear driving terms induced
  by the systematic MB field imperfections, with a
  phase split per arc increased from 0 to p from
  LHCV0 to LHCV5 (overall tune split of 5) and then
  no longer touched since more than 10 years!
• Under these conditions, no way to generate a
  coherent dispersion wave with orbit bumps in the
  arcs or a coherent off-momentum b-beating wave
  with the lattice MSs, big enough to actively
  compensate the chromatic aberrations induced by
  the triplet.
• Re-phase appropriately the 8 LHC IRs
• The IR phases are generally optimized for
  aperture, but generally offers some tunability.
• Since two sectors of sextupoles are needed to
  compensate for one IT (see next slides),
  IR2/4/6/8 play the role of phase trombone between
  two adjacent sectors w.r.t. the off-momentum
  b-beating and therefore need to be rematched with
  an appropriate phase.
• Then the left and right phase advances of IR1/5
  need to be constrained individually such that the
  compensation with the incoming waves from the arc
  (dispersion or off-momentum b-beating) arrives at
  the right phase in the IT.

? These aspects were missed in the conceptual
design of the LHC optics (not needed?) ? A new
overall LHC optics is needed for PhaseI to be
already tested/used for nom. (?)
S. Fartoukh, LIUWG 26/03/2009
7

• ? All LHC sectors and IRs needs to rematched
  according to the following phasing conditions

Schematic vertical off-momentum beta-beating wave
induced by the SD families of sectors 34 and 45

• Basically one MS family out of two per plane and
  per sector is efficient to compensate for the
  triplet.
• For the Phase I triplet (120 T/m), this limits
  the minimum possible b to 30cm (limits from the
  SD families assuming a max current of 550A)
  compared to 15 cm if only correcting Q.
• The phasing conditions above are also optimum
  for correcting the spurious dispersion (next
  slide).
• mcell as close as possible to p/2 is needed for
  efficiency (otherwise decoherence of the b-wave
  or disp. wave) and to avoid the generation of
  residual Q by the MS themselves ? substantial
  left/right tunability of IR1 IR5 is needed.
• ? Due to limited L/R tunability of IR1 and IR5,
  the arc MQTs (acting independently on both
  beams) gets a non-zero nominal setting, i.e. the
  LHC IRs now extends up to Q22 with some impact
  on the aperture _at_ 450 GeV (CO to be tighten by
  0.3 mm).
• ? The adjustment of the fractional part of the
  tune becomes tricky, and impose to detune in a
  subtle way the above phasing conditions e.g.
  dephasing sector 45 by DQ/2 and sector 34 by
  3DQ/2 give a tune shift of DQ while warranting
  that the b-wave still arrive with the right
  phase in the triplet.
• ? The MS efficiency and then the min. achievable
  b depend (smoothly) on the working point.

S. Fartoukh, LIUWG 26/03/2009
8
SLHCV1.0 (1/5) a new LHC overall optics for
PhaseI

• A new overall LHC optics with appropriate phasing
  properties has been constructed to allow the
  b(d) correction in collision, with controllable
  and/or correctable side effects (spurious H/V
  disp., b(d), Q, Q).
• Overall tune split of 3 (63.28/60.31 ?
  63.31/60.32 at injection?collision)
• Arc optics QF/QD strength all different in the 8
  LHC sectors (with some symmetries) and arc quad.
  MQTs (from Q14 to Q22) with non-zero nominal
  settings (essentially the QTFs).
• IRs New phase advance in the 8 LHC IRs (with
  some symmetries), fulfilling aperture constraints
  _at_450 GeV, and left/right phase of IR15
  constrained individually in collision.

S. Fartoukh, LIUWG 26/03/2009
9
SLHCV1.0 (2/5)

• Off-momentum beta-beating amplitude W(s) (linear)
  with b30 cm in IR15 and b10 m in IR28

IP3
IP5
IP1
IP1
IP7
Before correction
After correction
S. Fartoukh, LIUWG 26/03/2009
10
SLHCV1.0 (3/5)

• Off-momentum beta-beating versus d at specific
  locations after correction (b30 cm in IR15 and
  b10 m in IR28)

Db(d)/b(0) in the triplet of IR5
Db(d)/b(0) in the triplet of IR1
lt 2 _at_ 1.5 permil!
Db(d)/b(0) in IP3
Db(d)/b(0) in IP7
S. Fartoukh, LIUWG 26/03/2009
11
SLHCV1.0 (4/5)

• Tune vs d at specific locations (b30 cm in
  IR15 and b10 m in IR28)

Huge Q and Q
If needed, fine tuning with MOs (200/500A
needed in OF/OD)
Before correction
Almost linear up to 1.5 permil
After correction (Some SD families pushed up to
550A)
Residual Q (3000?6000) (b(d,s) ? 0 at the
sextupoles)
S. Fartoukh, LIUWG 26/03/2009
12
SLHCV1.0 (5/5)

• Correction of spurious dispersion via small orbit
  bumps

Several meters in the triplets
V- Xing in IR2
H- Xing in IR8
Closed orbit dispersion before correction
H- Xing in IR5
V- Xing in IR1
Closed H-orbit bumps in sectors 45 56 (closed
at Q11)
Closed orbit dispersion after correction
Closed V-orbit bumps in sectors 12 81 (closed
at Q11)
S. Fartoukh, LIUWG 26/03/2009
13
Layout and optics of IR1IR5 (1/3)

• Layout (l23.0 m)
• Symmetric triplet (MQXC/D types)
• ? 120 mm coil ID.
• ? 122.7 T/m nom. gradient (fine-tuned to find
  suitable slots for bi-directional BPMSs).
• ? 1 warm BPMs in front of Q1, 2 cold BPMs in
  between Q2ab and at the non-IP side of Q3.
  Possibly another BPM on the non-IP side of D1.
• Corrector package (CP) with MCBX, MQSX, MCSX,
  (MCTX?) lumped on the non-IP side of Q3 (?.. See
  later for the MCBX).
• New D1 (180 mm aperture, 30Tm ITF, 2 modules per
  D1).
• New TAS (48 mm aperture) and possibly new TAN
  with wider aperture(?).
• Nominal matching section!!

Courtesy of H. Prin
S. Fartoukh, LIUWG 26/03/2009
14
Layout and optics of IR1IR5 (2/3)

• Injection optics b14 m (could go higher or
  deeper if needed)

Injection crossing scheme (/-2.5 mm parallel
sep. and /- 175 mrad Xing angle)
Injection Optics with b14m
No comment but a nice clearance in the MS and
IT!
n1 plot from Q13 to Q13 (n17.0/6.7 _at_QF/QD
preserved)
S. Fartoukh, LIUWG 26/03/2009
15
Layout and optics of IR1IR5 (3/3)

• Low-P collision optics with b30 cm going
  deeper makes the MS settings unstable
  Q7?200T/m, Q5/Q6?0

nom. LHC rematched to b25cm (see LIUWG2) P
b/a 1km at the IT exit
bmax10.5 km _at_b30cm
Not a simple homothety w.r.t nom. LHC ?
Squeeze???
Triplet matched with small P b/a 320 m at
the Q3 exit
136 T/m IT matched to b25cm (see case Ib
LIUWG15) P b/a 330 m at the Q3 exit
bQ4 2 km minimized for MS aperture
Similar topology
Low-P collision optics for Phase I with b30
cm and specific L/R phase advances
S. Fartoukh, LIUWG 26/03/2009
16
Hor. collision crossing scheme for b30cm
(/-0.5 mm parallel sep. and /- 205 mrad Xing
angle)
D2/Q4
Q5
D1
TAN
TAS
n1 plot from Q7 to Q7 with octagonal IT
beam-screen (see N. Kos LIUWG14)

• ? n17.5 in the IT (w/o correcting the spurious
  dispersion)
• ? Nice clearance (n111?14) in the MS given by
  low-P optics.
• The TAN is the bottle-neck (but still n1gt7 for
  bgt30cm). It becomes a wonderful 3.5 m Cu TCT and
  TCLP for incoming and outgoing beams (but single
  jaw and not movable)!!!
• Whats about the alignment and rectitude of the
  vac. chambers in the zone??

• See presentation by J. Miles later in April for a
  detailed analysis of the IT and MS aperture vs
  X-angle orientation, and pros and cons for
  race-track/octagonal b.s. shape.

Idem with LHC type screens oriented vs
X-scheme ?Marginal gain
S. Fartoukh, LIUWG 26/03/2009
17
? Dn11.5 gained correcting the spurious
dispersion
N19
N17
n19 almost reached in the TAN IT

• but with a non-zero nominal CO in the arcs,
  orthogonal fine tuning knobs must be defined
  (for orbit, tune, coupling, b, Dx,y ,Q and
  b(d)) ?Robustness, operational aspects.

S. Fartoukh, LIUWG 26/03/2009
18
Available tools

• ? New directory created under /afs/cern.ch/eng/lh
  c/optics
• SPS TD68 TI2old V1 V3 V4.1 V4.3 V5
  V6.0 V6.2 V6.3 V6.5 V6.501 V6.50x SLHCV1.0
  TD62 TI2 TI8 V2 V4.0 V4.2 V4.x V5.0
  V6.1 V6.-2 V6.4 V6.500
• In construction phase but already containing
  several madx sample jobs to perform various kind
  of studies, optics files, toolkits, aperture
  model, field error generation routines and error
  table of the new IT/D1,
• aperture/ SLHCV1.0.inj.thin.str
  removeinstall.madx
• archive/ SLHCV1.0.inj.str
  job_aperture.madx
• errors/ IR15.coll.str
  job_fortracking.madx
• toolkit/ IR15.coll.thin.str
  job_forITcorrectorspec.madx
• 
  samplejob_general.madx
• 
  compare_optics_thicktothin.madx

S. Fartoukh, LIUWG 26/03/2009
19
On-going prioritary studies, preliminary results
and future plans (1/3)

• Basic optics checks done (settings, aperture _at_450
  GeV) but still waiting for an official stamp
  from BI/BT/RF for the new IR2/4/6/8 optics.
• Aperture still OK (max. loss of Dn1 0.1) even
  with a CO budget of 4 mm at injection, rather
  pessimistic for Phase I.
• Nevertheless, the lack of IR tunability _at_ 450GeV
  is worrying
• not sure that an SLHCV1.0-like-optics could
  still be found if the LHC working point 0.28/.31
  will have to be substantially modified the beam
  will tell!
• Detailed aperture checks in collision for
  different b.s. shape, versus X-scheme
  orientation almost completed (J.Miles).
• Squeeze sequence not yet started (will be
  difficult!), foreseen for May-June, but after
  converging on the detailed triplet layout (see
  below) and then high-beta optics
• CO correct-ability with triplet misalignments
  assuming only one MCBX per plane on the non-IP
  side of Q3 on-going (R. Tomas) with already
  strong limitations found ? next slide.

S. Fartoukh, LIUWG 26/03/2009
20
Probability of success of short-length orbit
correction from Q7 to Q7, peak orbit deviation
in the IT, and loss of b-b separation versus ptp
MQX misalig.s (100 seeds for each case)
Preliminary
Courtesy of R. Tomas
Nominal b-b sep. at BPM2 3 (in units of the
smallest beam1/2 sigma)

• Not enough strength in the MCBC/MCBY _at_ Q4/5/6/7
  to cope with ptp MQX misalignments larger than
  0.4-0.5 mm (MCBXH/V below 3T/m at this level
  compared to 6Tm specified) and then nothing left
  to move the vertex by /-0.5mm as always granted
  to the experiment!!!
• Additional non-common two-in-one H/V corrector
  on the non-IP side of Q4 could help relaxing the
  IT mechanical spec.s but will not improve the
  locality (otherwise difficult squeeze!) and
  quality (peak CO in the IT, b.-b. separation) of
  the correction ? study on-going
• The recommendation will certainly be an
  additional MCBXH/V attached to the c.m. of
  Q2a/Q2b, but then hard time to find good slots
  for the bi-directional BPMSs?!

S. Fartoukh, LIUWG 26/03/2009
21
On-going prioritary studies, preliminary results
and future plans (2/3)

• IT corrector spec.s reviewed (B. Holzer, see
  next slide)
• 30 T/m over 50 cm mag. length for the MQSX (to
  cope with up 2 mrad IT roll angle errors as in
  the nom. LHC MQSX).
• 0.04 Tm _at_ Rr40 mm for the MCSX (based on error
  table V1 for IT/D1)
• 0.08 Tm _at_ Rr40 mm for the MCTX (need still to
  be demonstrated via tracking).
• No MCSSX(a3), MCOSX(a4), MCOX(b4) yet foreseen
  (tracking will tell!!)
• Dynamic aperture on-going (B. Holzer)
• Top priority DA _at_ 450 GeV (new optics with a
  tune split of 3).
• Then DA in collision and assessment of the new
  D1/IT field quality.
• All necessary MADX tools already built and
  available in SLHCV1.0 directory.
• Modification of the SIXTRACK environment still
  needed to start with the massive tracking
  campaign
• First results expected end of April.
• Missing info (for completeness) IT error table
  expected at injection error tables for the
  contribution expected from IT beam-screen.

S. Fartoukh, LIUWG 26/03/2009
22
MQSX (a2)
MCSX (b3)
MCTX (b6) .. if needed(?)
IT corrector strength in of Kmax for 4 70
different seeds
Courtesy of B. Holzer
S. Fartoukh, LIUWG 26/03/2009
23
On-going prioritary studies, preliminary results
and future plans (3/3)

• Beam-beam (E. Laface F. Schmidt)
• 24 additional parasitic collisions (19/15 per
  IP side up to the D1 entry for SLHCV1/V6.503).
• First MADX tools updated for SLHCV1 (see next
  slide)

SLHCV1 10s b.-b. sep. in the drift
Nominal LHC 9.5s b.-b. sep. in the drift
Courtesy of E. Laface
Courtesy of E. Laface
S. Fartoukh, LIUWG 26/03/2009
24
Courtesy of E. Laface

• Size of the Tune footprint reduced for SLHCV1
  head-on reduced due
• to the increased of the Piwinsky angle by a
  factor of 1.9, idem slightly for parasitic (see
  below).
• Slight H/V dissymmetry visible on the tune
  footprint due to the use of the Landau octupoles
  for residual Q correction in collision (ODs
  twice stronger than OFs).
• Peak Lumi of 31034 cm-2s-1 potentially reached
  at ultimate beam intensity

S. Fartoukh, LIUWG 26/03/2009
25
Summary

• The LHC IR phase I upgrade cannot be resumed to a
  simple exchange of the IR1 and IR5 inner
  triplets.
• New ingredients, in particular the correction of
  the chromatic aberrations leading to a deep
  modification of the LHC overall optics, imposes
  to re-launch a battery of studies to demonstrate
  the viability of the proposal.
• Already several potential improvements and gains
  w.r.t. V6.503, but relying on a challenging
  control of the linear optics in collision
  (betatron phases!!)
• 1. Off-momentum b-beat now corrected both in
  IR3/7 and in the ITs of IR15.
• b up to 30 cm in collision (limited by SD
  strength _at_550A) corresponding to factor 1.4/3.0
  on the peak lumi at nominal/ultimate current,
  with possibly n1 9 in the IT (after correction
  of the spurious dispersion)
• Several possible show-stoppers to be investigated
  in 2009 DA _at_450 GeV (new optics with tune split
  of 3), beam-beam _at_ 7TeV .
• Several grey zones and HW decisions to be taken
  hopefully in the direction of considering phaseI
  first as a consolidation of the nominal LHC, e.g.
  additional MCBX between Q2a/Q2b, symmetric
  triplet (2 MQX type) or super-symmetric (1 single
  MQX length)?...

S. Fartoukh, LIUWG 26/03/2009