a new overall lhc optics for the lhc ir upgrade phase i from new concepts (liuwg#15, may 2008) to a...

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

• Chromatic aberrations at low *, 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 * (1/3)• Off-momentum -beating, NL chromaticity Q” and Q”’- Strategy for V6.503 (IR1 & 5 with =55 cm): Passive compensation between IR1&5 by /2 betatron phasing between IP1 & IP5. Off-momentum -beating bump between IR1 and IR5 reaching ~40% @ =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 =25 cm):

Linear off-mom. -beat minimized in IR7 but reaching ~100% @ =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 -

beat (…the phase advance from IP1 to IP5 is no longer /2 for non-zero ).

… See illustrations in next slides (coming from LIUWG#15 presentation)


IP3IP1 IP5 IP7 IP1

W ~ 1000 in IR3 W ~ 0 in IR7 and in the new triplets

Linear “Montague” function Wx,y (s)~| ∂/∂(s)/(s)|amp.

Tune v.s. Qx,y

Bu

cket:

×

Min

. mom

entu

m w

ind

ow:

Mon

. collimator:

×

Beam life time and background to the experiments when moving by a few 10-4 , e.g. for dispersion or chromaticity measurement?? Where the diffracted protons escaping IR3 (i.e. with < a few permil) will be lost?? For them the off-momentum -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. -beating in the new IT’s and IR7??.. See next slide.

V6.503 but in IR1 & 5 with =25cm and new IT (see LIUWG#15)


in the triplet of IR1

Lin. term corrected Large sec. order


Lin. term corrected Large sec. order

in IP7 Lin. term correctedHigher order effects

(much bigger at some TCP)

in IP3 Lin. term not corrected

Large sec. order

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

Off-momentumTriplet aperture!

Collimation efficiency,even after phasing IP1 and IP5?


Chromatic aberrations at low * (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!!

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 Q13and matched to zero in IP1,2,5 &8)

IP1 IP5 IP1

H-dispersion generated on purpose in IR3

V6.503 but in IR1 & 5 with =25 cm and new IT (see LIUWG#15)


Chromatic aberrations at low * (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 ~ 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 -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 off-momentum -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 -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 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).cell as close as possible to /2 is needed for efficiency (otherwise decoherence of the ’-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 –Q/2 and sector 34 by +3Q/2 give a tune shift of +Q while warranting that the ’-wave still arrive with the right phase in the triplet.

The MS efficiency and then the min. achievable depend (smoothly) on the working point.


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 ’() correction in collision, with controllable and/or correctable side effects (spurious H/V disp., ’’(), Q’’, Q’’’).

Overall tune split of 3 (63.28/60.31 63.31/60.32 at injectioncollision) 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 x / [2] and

MQT settingsV6.503 SLHCV1.0

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

1012A @ 450 GeV

23A @ 450 GeV

IR phase

x / [2]

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 *=30 cm in IR1&5 and *=10 m in IR2&8

Before correction After correction

IP1 IP3 IP5 IP1IP7


SLHCV1.0 (3/5)• Off-momentum beta-beating versus at specific

locations after correction (*=30 cm in IR1&5 and *=10 m in IR2&8)


in IP3


in IP7


SLHCV1.0 (4/5)• Tune vs at specific locations (*=30 cm in IR1&5 and *=10 m in IR2&8)

After correction(Some SD families pushed up to 550A)

Residual Q’’ (~30006000) (’(s≠ at the sextupoles)

Huge Q’’ and Q’’

Before correction

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

H- Xing in IR5

V- Xing in IR2 H- Xing in IR8

V- Xing in IR1

Closed H-orbit bumpsin sectors 45 & 56 (closed at Q11)

Closed V-orbit bumpsin sectors 12 & 81 (closed at Q11)

Closed orbit & dispersion

before correction

Closed orbit & dispersion

after correction

Several meters in the triplets


Layout and optics of IR1&IR5 (1/3)• Layout (l*=23.0 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 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!!

Courtesy of H. Prin


Layout and optics of IR1&IR5 (2/3)• Injection optics: *=14 m (could go higher or deeper if needed)

Injection Optics with*=14mInjection crossing scheme

(+/-2.5 mm parallel sep. and +/- 175 rad Xing angle)

n1 plot from Q13 to Q13(n1=7.0/6.7 @QF/QD preserved)

No comment…but a nice clearance in

the MS and IT!S. Fartoukh, LIUWG 26/03/2009

Layout and optics of IR1&IR5 (3/3)• “Low-P” collision optics with *=30 cm: going deeper makes the

MS settings “unstable”: Q7200T/m, Q5/Q60

max~10.5 km@*=30cm

Q4 ~ 2 km minimizedfor MS aperture

Triplet matched with small P = ~ 320 m at the Q3 exit

nom. LHC rematched to *=25cm (see LIUWG#2):

P = ~ 1km at the IT exit

136 T/m IT matched to *=25cm (see case Ib: LIUWG#15):

P = ~ 330 m at the Q3 exit

Low-P collision optics for Phase I with *=30 cm and specific L/R phase advances

Not a simple homothety w.r.t nom. LHC Squeeze???

Similar topology


Hor. collision crossing scheme for *=30cm (+/-0.5 mm parallel sep. and +/- 205 rad Xing angle)

n1 plot from Q7 to Q7 with octagonal IT beam-screen(see N. Kos LIUWG#14)

Idem with LHC type screensoriented vs X-scheme:

Marginal gain

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.

D1

D2/Q4

Q5

S

n1~7.5 in the IT (w/o correcting the spurious dispersion) Nice clearance (n1=1114) in the MS given by “low-P optics”. The TAN is the bottle-neck (but still n1>7 for *>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??


n1~1.5 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, , Dx,y ,Q’ and ’()) Robustness, operational aspects.


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/ 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


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 n1 ~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.


Courtesy of R. Tomas

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)

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?!

Nominal b-b sep. at BPM2 & 3(in units of the smallest beam1/2 sigma)



• 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.



Courtesy of B. Holzer

IT corrector strength in % of Kmax for 4 × 70 different seeds

MQSX (a2)

MCTX (b6) .. if needed(?)

MCSX (b3)


• 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).

First MADX tools updated for SLHCV1 (see next slide)

Courtesy of E. Laface


Courtesy of E. LafaceNominal LHC: 9.5b.-b. sep. in the drift

SLHCV1: 10b.-b. sep. in the drift


Courtesy of E. Laface

Size of the Tune footprint reduced for SLHCV1: head-on reduced dueto 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 3×10 cm-2s-1potentially reached at ultimate beam intensity

Summary• The LHC IRIR 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 -beat now corrected both in IR3/7 and in the IT’s of IR1&5. * 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 super-symmetric (1 single MQX length)?...


a new overall lhc optics for the lhc ir upgrade phase i from new concepts (liuwg#15, may 2008) to a...

Documents