Transcript Document

A new overall LHC optics for
the LHC IR upgrade Phase I
From new concepts (LIUWG#15, May 2008)
to a complete solution
S. Fartoukh for the ABP Upgrade Team 26/03/2009
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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 @450 TeV & 7 TeV, beam-beam
Conclusions
S. Fartoukh, LIUWG 26/03/2009
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 IR1&5 by p/2 betatron phasing between IP1 & IP5.
 Off-momentum b-beating bump between IR1 and IR5 reaching ~40% @ d=0.001.
 Probably OK for collimation (R. Assmann, LIUWG#4) 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% @ d=0.001 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 bbeat (…the phase advance from IP1 to IP5 is no longer p/2 for non-zero d).
… See illustrations in next slides (coming from
LIUWG#15 presentation)
S. Fartoukh, LIUWG 26/03/2009
V6.503 but in IR1 & 5 with b* =25cm and new IT (see LIUWG#15)
IP5
IP7
IP1
Linear “Montague” function
Wx,y (s)~| ∂b/∂d (s)/b(s)|amp.
Min. momentum window: d = 10-3
IP3
Bucket: d = 0.36×10-3
IP1
W ~ 0 in IR7 and
in the new triplets
Mon. collimator: d = 1.5×10-3
W ~ 1000 in IR3
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 d< 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 IT’s!!
 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 IT’s and IR7??.. See next slide.
S. Fartoukh, LIUWG 26/03/2009
Db(d)/b(0) [%]
in the triplet of IR1
 Lin. term corrected
 Large sec. order
Off-momentum
Triplet aperture!
Db(d)/b(0) [%] in IP3
 Lin. term not corrected
 Large sec. order
Db(d)/b(0) [%]
in the triplet of IR5
 Lin. term corrected
 Large sec. order
Db(d)/b(0) [%] in IP7
 Lin. term corrected
Higher order effects
(much bigger at some TCP)
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
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!
V6.503 but in IR1 & 5 with b*=25 cm and new IT (see LIUWG#15)
IP1
IP5
IP1
With X-scheme
~ 5 - 6 m in MQX (beam1-2)
 substantially modified in IR3/7
H-dispersion generated
on purpose in IR3
Dxy(s) w/o X-scheme
(arc-regular from Q13 to Q13
and matched to zero in IP1,2,5 &8)
 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!!
S. Fartoukh, LIUWG 26/03/2009
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 MS’s,
big enough to actively compensate the chromatic aberrations induced by the triplet.
Re-phase appropriately the 8 LHC IR’s
- 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 offmomentum 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 offmomentum 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
 All LHC sectors and IR’s 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 MQT’s (acting independently on both beams) gets a non-zero nominal
setting, i.e. the LHC IR’s now extends up to Q22 with some impact on the aperture @ 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
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. MQT’s (from Q14 to Q22) with non-zero nominal settings (essentially the QTF’s).
 IR’s: New phase advance in the 8 LHC IR’s (with some symmetries), fulfilling aperture
constraints @450 GeV, and left/right phase of IR1&5 constrained individually in collision.
Arc cell phase and
Dmx / Dmy [2p] and
MQT settings
V6.503
Sector 12
0.2635 / 0.2431
0.2598 / 0.2500
Sector 23
0.2635 / 0.2431
0.2531 / 0.2489
Sector 34
0.2635 / 0.2431
0.2530 / 0.2486
Sector 45
0.2635 / 0.2431
0.2600 / 0.2504
Sector 56
0.2635 / 0.2431
0.2598 / 0.2500
Sector 67
0.2635 / 0.2431
0.2541 / 0.2488
Sector 78
0.2635 / 0.2431
0.2525 / 0.2483
Sector 81
0.2635 / 0.2431
0.2600 / 0.2504
MQTF
MQTD
0
0
S. Fartoukh, LIUWG 26/03/2009
SLHCV1.0
1012A @ 450 GeV
23A @ 450 GeV
IR phase
Dmx / Dmy [2p]
and overall tune
V6.503
SLHCV1.0
Beam1
Beam2
Beam1
Beam2
IR2
2.974 / 2.798
2.991 / 2.844
3.020 / 2.900
3.020 / 2.900
IR8
3.183 / 2.974
3.059 / 2.782
3.020 / 2.900
3.020 / 2.900
IR3
2.248 / 1.943
2.249 / 2.007
2.255 / 1.955
2.255 / 1.955
IR4
2.143 / 1.870
2.143 / 1.870
2.260 / 1.650
2.260 / 1.650
IR6
2.015 / 1.780
2.015 / 1.780
2.010 / 1.900
2.010 / 1.900
IR7
2.377 / 1.968
2.483 / 2.050
2.455 / 1.970
2.455 / 1.970
IR1&IR5
2.633 / 2.649
2.633 / 2.649
2.670 / 2.644
2.670 / 2.644
IR1 & IR5 left
Never specified
1.070 / 1.754
1.605 / 0.890
IR1 & IR5 right
Never specified
1.600 / 0.890
1.065 / 1.754
Qx/Qy
64.31/59.32
63.31/60.32
SLHCV1.0 (2/5)
• Off-momentum beta-beating amplitude W(s) (linear)
with b*=30 cm in IR1&5 and b*=10 m in IR2&8
IP1
Before correction
S. Fartoukh, LIUWG 26/03/2009
IP3
IP5
IP7
After correction
IP1
SLHCV1.0 (3/5)
• Off-momentum beta-beating versus d at specific
locations after correction (b*=30 cm in IR1&5 and b*=10 m in IR2&8)
Db(d)/b(0) [%]
in the triplet of IR1
Db(d)/b(0) [%]
in the triplet of IR5
Db(d)/b(0) [%]
in IP3
Db(d)/b(0) [%]
in IP7
S. Fartoukh, LIUWG 26/03/2009
SLHCV1.0 (4/5)
• Tune vs d at specific locations (b*=30 cm in IR1&5 and b*=10 m in IR2&8)
Huge Q’’ and Q’’
Before correction
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
If needed,
fine tuning with MO’s
(~200/500A needed in OF/OD)
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
Layout and optics of IR1&IR5 (1/3)
• Layout (l*=23.0 m)
 Symmetric triplet (MQXC/D types)
 120 mm coil ID.
Courtesy of H. Prin
 122.7 T/m nom. gradient (fine-tuned to find suitable slots for bi-directional BPMS’s).
 1 warm BPMs in front of Q1, 2 cold BPM’s in between Q2a&b 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!!
S. Fartoukh, LIUWG 26/03/2009
Layout and optics of IR1&IR5 (2/3)
• Injection optics: b*=14 m (could go higher or deeper if needed)
Injection Optics with b*=14m
n1 plot from Q13 to Q13
(n1=7.0/6.7 @QF/QD preserved)
S. Fartoukh, LIUWG 26/03/2009
Injection crossing scheme
(+/-2.5 mm parallel sep. and +/- 175
mrad Xing angle)
No comment…
but a nice clearance in
the MS and IT!
•
Layout and optics of IR1&IR5 (3/3)
“Low-P” collision optics with b*=30 cm: going deeper makes the
MS settings “unstable”: Q7200T/m, Q5/Q60
nom. LHC rematched to b*=25cm
(see LIUWG#2):
P = b/a ~ 1km at the IT exit
b max~10.5 km
@b*=30cm
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 b*=25cm
(see case Ib: LIUWG#15):
P = b/a ~ 330 m at the Q3 exit
b Q4 ~ 2 km minimized
for MS aperture
Similar topology
Low-P collision optics for Phase I with
b*=30 cm and specific L/R phase advances
S. Fartoukh, LIUWG 26/03/2009
Hor. collision crossing scheme for b*=30cm
(+/-0.5 mm parallel sep. and +/- 205 mrad Xing angle)
D2/Q4
Q5
D1
TAS
TAN
n1 plot from Q7 to Q7 with
octagonal IT beam-screen
(see N. Kos LIUWG#14)
 n1~7.5 in the IT (w/o correcting the spurious dispersion)
 Nice clearance (n1=1114) in the MS given by “low-P optics”.
 The TAN is the bottle-neck (but still n1>7 for b*>30cm). It
becomes a wonderful 3.5 m Cu TCT and TCLP for incoming and
outgoing beams (but single jaw and not movable)!!!
 What’s about the alignment and rectitude of the vac. chambers
in the zone??
Idem with LHC type screens
oriented vs X-scheme:
Marginal gain
See presentation by J. Miles later in April for a
detailed analysis of the IT and MS aperture vs Xangle orientation, and pros and cons for racetrack/octagonal b.s. shape.
S. Fartoukh, LIUWG 26/03/2009
 Dn1~1.5 gained correcting the spurious dispersion
N1=9
N1=7
… 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
Available tools
 New directory created under /afs/cern.ch/eng/lhc/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/
errors/
toolkit/
SLHCV1.0.inj.str
IR15.coll.str
IR15.coll.thin.str
S. Fartoukh, LIUWG 26/03/2009
job_aperture.madx
job_fortracking.madx
job_forITcorrectorspec.madx
samplejob_general.madx
compare_optics_thicktothin.madx
On-going prioritary studies,
preliminary results and future plans (1/3)
• Basic optics checks done (settings, aperture @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 @ 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
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)
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 @ 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 BPMS’s?!
S. Fartoukh, LIUWG 26/03/2009
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 @ Rr=40 mm for the MCSX (based on error table V1 for IT/D1)
 ~ 0.08 Tm @ Rr=40 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 @ 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
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
On-going prioritary studies,
preliminary results and future plans (3/3)
• Beam-beam (E. Laface & F. Schmidt)
 2×4 additional parasitic collisions (19/15 per IP side up to the D1 entry for
SLHCV1/V6.503).
SLHCV1: 10s b.-b. sep. in the drift
Nominal LHC: 9.5s b.-b. sep. in the drift
Courtesy
CourtesyofofE.E.Laface
Laface
 First MADX tools updated for SLHCV1 (see next slide)
S. Fartoukh, LIUWG 26/03/2009
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 (OD’s ~twice stronger than
OF’s).
 Peak Lumi of 3×1034 cm-2s-1 potentially reached at ultimate beam intensity
S. Fartoukh, LIUWG 26/03/2009
Summary
•
•

1.
2.


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!!):
Off-momentum b-beat now corrected both in IR3/7 and in the IT’s of IR1&5.
b* up to 30 cm in collision (limited by SD strength @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 @450 GeV
(new optics with tune split of 3), beam-beam @ 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 supersymmetric (1 single MQX length)?...
S. Fartoukh, LIUWG 26/03/2009