HL-LHC optics
S. Fartoukh, CERN-BE-ABP
 Performance goal & basic ingredients
 Optics & beam parameters
 Optics limitations & the Achromatic Telescopic
Squeezing (ATS) scheme
 HL-LHC optics using the ATS
 The preliminary HL-LHC shopping list
 Conclusions
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
1
Performance goal & basic ingredients
  L = 3000 fb-1 from  2022-2023 to  2035
 250 fb-1 / year (estimated to 150 days of operation)
 heff  40% machine efficiency required running at a
levelled luminosity of Llev = 5 × 1034
 Long fill required ( 10h including decay)
compared to average turn around
(estimated to  5h for LHC) to push heff
 Ingredients:
Ideal case, F. Zimmerman
1. Higher current (× 1.5  × 1.9) first for beam life time.
2. Smaller emittance (÷1.25  ÷1.5) for “virtual luminosity”.
3. Smaller b* (÷4  ÷12) for “virtual luminosity”.
4. Crab-cavity (or flat optics with shorter bunch length) for “virtual luminosity”.
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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Baseline Optics & Beam Parameters
LHC nominal
HL-LHC
25 ns
HL-LHC
50 ns
2808
2808
1404
1.15 (0.58A)
2.2 (1.11 A)
3.5 (0.88 A)
gex,y [mm]
3.75
2.5
3.0
eL [eV.s]
2.5
2.5
2.5
sz [cm]
7.5
7.5
7.5
sdp/p [10-3]
0.1
0.1
0.1
b* [cm]
55
15
15
285 (9.5 s)
590 (12.5 s)
590 (11.4 s)
Lumi loss factor
0.84
0.30
0.33
Peak lumi [1034]
1.0
7.2
8.3
1.2
21.7
23.1
Tleveling [h] @ 5E34
n/a
8.9
7.3
#Pile up @5E34
25
123
247
# Bunches
p/bunch [1011]
X-angle [mrad]
Virtual lumi [1034]
Latest HL-LHC beam parameters
worked out by O. Brüning
 25 ns is the baseline, 50 ns is a back-up (e.g.
for e-cloud).
 Full agreement not yet reached with the LHC
Injector Upgrade project (e.g. 3 mm offered
instead of 2.5 mm emittance for the 25 ns case,
but 2.2E11 bunch charge possibly reachable!)
(with hour-glass effect)
 Heavily relies on crab-cavity with a bare
minimum of 10 MV / beam/ IR side.
 Prepare variants for the HL-LHC optics with even smaller b* and/or flat optics (back-up in the
absence of crab-cavity)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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Optics Parameters (baseline & variants)
Optics parameters
“Baseline-HL”
“Stretched-HL”
Injection @ 450 GeV
b* [m]
5.5
5.5
Full Xangle [mrad]
490
490
2
2
Half-parallel separation [mm]
Collision round @ 7 TeV (X-angle set to 12.5s at 2.5 mm emittance)
b* [m]
0.15
0.10
Full Xangle [mrad]
590
720
Collision flat @ 7 TeV (crossing in the plane of biggest b*, set to 16.5 s at 2.5 mm emittance)
b* [m]
(aspect ratio of 4 found optimal for aperture)
Full Xangle [mrad]
0.30/0.075
0.20/0.05
550
670
 All these optics are now available in the latest optics & layout version of the HL-LHC:
SLHCV3.1b (150 T/m-140 mm Nb3Sn IT)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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A small digression: Why more than 10s for the X-angle ?
 Tune footprint at 6s with 21 LR’s per IP side (longer IT), HO at IP1 and IP5, b*=15 cm and
beam parameters (higher bunch charge) given in the previous table
25 ns, 10s (475 mrad)
50 ns, 10s (520 mrad)
25 ns, 590 mrad (12.5s)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
50 ns, 590 mrad (11.4s)
5
 100’000 turns DA simulation results vs. X-angle confirming the “pathological tune
footprint” (25 ns beam parameters, b*=15 cm, only sextupoles, LR and HO, no crabcrossing no field imperfection)
Preliminary results from S. White
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
6
Optics Limitations & the ATS scheme (1/2)
 Lowering b* needs magnets of larger aperture, but also new
hardware or sophistication (crab-cavity, flat optics,...) to mitigate the
luminosity loss due to the Piwinsky angle.
 How to produce this b* ???
This is the aim of the ATS scheme which solves many optics
limitations coming from the overall LHC ring.
1. Optics matchability to the arcs:
–
Some IR quads going to 0 T/m, others to max. field (200T/m).
–
Simply the matching section becomes too short at some point.
2. Correctability of the chromatic aberrations induced, not only Q’,
but also Q’’, Q’’’,…, and off-momentum b-beating:
– limitations from the arc sextupole strength (<600A).
... Otherwise b* would be limited to 30 (25) cm with the NbTi (Nb3Sn)
technology and indeed 120 mm would be optimum for the IT
aperture !!!
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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Optics Limitations & the ATS scheme (2/2)
• A new injection optics (p/2 FODO lattice  new integer tunes)
• A squeeze in 2 steps
1) An “almost” standard squeeze, the Pre-squeeze:
 acting on the matching quads of IR1 and IR5,
 with new matching constraints on the left/right IR phase
 till reaching some limits (sextupoles, matching quadrupoles).
2) A further reduction of b*, the Squeeze:
 acting on IR2/8 for squeezing IR1 and IR4/6 for IR5,
 inducing b-beating bumps in sectors 81/12/45/56 to boost
the sextupole efficiency at constant strength.

b
*
Squeeze
 b
*
Pre  Squeeze

(bˆ )
(bˆ )
Arc FODO
Arc Mismatched
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
8
HL-LHC optics using the ATS (1/8)
Injection optics b* = 5.5 m at IP1 and IP5 (150 T/m IT gradient)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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HL-LHC optics using the ATS (2/8)
Pre-squeezed optics b* = 40 cm at IP1 and IP5 (150 T/m IT gradient)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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HL-LHC optics using the ATS (3/8)
Round Squeezed optics b* = 10 cm at IP1 and IP5 (150 T/m IT gradient)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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HL-LHC optics using the ATS (4/8)
Flat Squeezed optics b* = 20/5 cm at IP1 and IP5 (150 T/m IT gradient)
bmax= 55 km
a factor of 12 above nominal!
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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Why does it work? The magic lies in the choice of the betatron phases
.. Zoom in arc45: Pre-Squeeze to b*= 40/40 cm (round optics)
Dmy  p between strong SD’s
(every other FODO cells)
Dmx  p between strong SF’s
(every other FODOcells)
Dmy (Q11 IP ) = 1.25×p + ey
with ey ~ 1/2 tan-1 (bmin/bmax)
(barc× b *)V  cst
Dmx(Q10 IP ) = 0.75×p + ex
with ex ~ - 1/2 tan-1 (bmin/bmax)
 (barc× b *)H  cst
 p/2 phase in the arc cells
 p/2 on the left/right side of the IR
 2 sextupole families per plane but
only one used for triplet correction
IR4
(RF insertion)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
IR5
(CMS insertion)
13
Why does it work? The magic lies in the choice of the betatron phases
.. Zoom in arc45: Squeeze to b*= 10/10 cm (round optics)
Dmy  p between strong SD’s
(every other FODO cells)
Dmx  p between strong SF’s
(every other FODOcells)
IR4
(RF insertion)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
Dmy (Q11 IP ) = 1.25×p + ey
with ey ~ 1/2 tan-1 (bmin/bmax)
(barc× b *)V  cst
Dmx(Q10 IP ) = 0.75×p + ex
with ex ~ - 1/2 tan-1 (bmin/bmax)
 (barc× b *)H  cst
IR5
(CMS insertion)
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Why does it work? The magic lies in the choice of the betatron phases
.. Zoom in arc45: Squeeze to b*= 20/5 cm (flat optics)
Dmy  p between strong SD’s
(every other FODO cells)
Dmx  p between strong SF’s
(every other FODOcells)
IR4
(RF insertion)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
Dmy (Q11 IP ) = 1.25×p + ey
with ey ~ 1/2 tan-1 (bmin/bmax)
(barc× b *)V  cst
Dmx(Q10 IP ) = 0.75×p + ex
with ex ~ - 1/2 tan-1 (bmin/bmax)
 (barc× b *)H  cst
IR5
(CMS insertion)
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Simulating the ATS in the existing LHC (IT @ 205 T/m) to deliver b*= 10 cm at IP1&5
Tunes vs. dp
IR4
IR5
IR6
Beam size [mm] and dispersion (IR4IR6)
at 3.5 TeV (for ge=3.5 mm)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
Chromatic Montague functions over the
full ring (off-momentum b-beating)
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HL-LHC optics using the ATS (5/8)
The new crossing bump is closed at D2 before the crab-cavity, but requires
1. strong 2-in-1 orbit corrector at D2 in the X-plane: 105 mm, 7 Tm
2. strong single bore orbit corrector on the nIP side of Q3: 140-150 mm, 4-5 Tm
Idea from R. de Maria
Standard crossing scheme
(closing at Q6)
07/05/2012
New crossing scheme
(closing at D2)
S. Fartoukh, CM18/HiLumi-LHC meeting
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HL-LHC optics using the ATS (6/8)
An additional functionality of the ATS optics:
 Correcting the huge spurious dispersion induced by the X-angle
ATLAS
LHCb
CMS
Alice
Up to 15-20 m of spurious
dispersion in the IT @ b*=10 cm!
H & V Dispersion
Closed orbit
Correction to less than 1m via
modest orbit bumps in the arcs
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
18
HL-LHC optics using the ATS (7/8)
Mechanical aperture: the largest is the better (“1 mm much more valuable than 1 T/m”)
Courtesy, R. De Maria
Target of 14s at 7 TeV extrapolated at constant
collimator & protection settings (in mm) from the
present operation @ 4TeV.
Target of 11.5s assuming new hardware (1-2 s less
might even be OK ... being worked out in WP5):
BPM at collimator (R. Assmann, R. Bruce, S. Redaelli
et al.) and/or more robust TCTH ( for IT protection
against asynchronous dump).
 Two cases showed: 140 mm IT/D1 with b*= 15 cm and 150 mm IT/D1 with b*= 10 cm
 Brute aperture, i.e. with no budget for CO, spurious dispersion, b-beating,...
 No beam-screen assumed in the IT/D1 but very thick cold bore (10 mm) for shielding
 New TAS, TAN, D2, Q4, Q5 (see later for the first aperture specification)
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
19
HL-LHC optics using the ATS (8/8)
Dynamic aperture
 see talk by Y. Cai on Tuesday afternoon
 ...the good field region is as important as the available aperture ... “good” means
IT harmonics of a few 10-5 at 7 TeV to be compatible with the b* range of HL-LHC!
In this respect, we should first convince ourselves that the Nb3Sn technology is the
right choice for HL-LHC.
 demonstrate rapidly that the 0.5-1 unit FQ level (at 2/3 of the aperture) is within
reach at 7 TeV, with good hope for further improvement (keeping in mind that the
requirements at 450 GeV are much less stringent, e.g. 20-30 units of b6 at Rr=50 mm).
 keep in mind the  0.5 TeV uncertainty for the final energy of the LHC within
which the FQ (e.g. b6) shall ideally not deviate by more than 0.1-0.2 unit w.r.t. 0.
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
20
The preliminary HL-LHC shopping list
1. HW re-commissioning & modifications needed for the ATS
- Re-commission at 600A the 16 SD families of sectors 81/12/45/56
- equip the 4 Q10’s of IR1/5 with an arc MSCB (sextupole + orbit corrector) instead of MCBC
- replace Q5 in IR6 (MQY type, 3.2 m ×160 T/m) by a longer magnet (MQYL, e.g. 4.8 m ×160 T/m)
2. The main shopping list for LSS1 and LSS5 (corrector not included)
Equipment
TAS
IT
Aperture [mm]
Separation [mm] (for 2-in-1)
Performance (T/m, T.m, MV,...)
60
n/a
n/a
140150 (w/o beam-
n/a
150 T/m 100 T/m
n/a
35 T.m  40 T.m (depending on IT
screen but shielding)
D1
140150 (more might be
needed for beam-screen)
length, i.e. on IT gradient)
TAN
41/37 (elliptical)
145
n/a
D2
105
186
35 T.m  40 T.m
Crab-cavity
80
194
10 MV per beam, per IR side
Q4
90
194
500 T/m×m
Q5
70
194
750 T/m×m
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
(+2.5MV to be fully compatible with b*=10cm)
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Conclusions
 Work already very well-advanced, but as usual devil is in the details.
 The field quality of the IT looks extremely challenging to fully profit
from the large IT aperture (and from the ATS)
 The crab-cavity voltage shall be pushed as much as we can if one
hopes to fully profit from b*= 15 cm, if not 10 cm.
 ... and first ATS machine experiments cannot be more encouraging!
ATS experiments at the LHC,
S. Fartoukh et al. at IPAC’12
After a single shift, a factor of only 2 was missing to demonstrate the HL-LHC b*!
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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... Reserve
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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What would happen for a “standard squeeze” to b*= 30 cm (120 T/m triplet) ?
550A
160 T/m
Transition @ b*=1.5 m
b*=30 cm
Q5/Q6 close to 0!
Matching section (MS)
07/05/2012
b*=30 cm
 550A!
- 550A
Sextupole powering scheme and
gradients (beam1) at 7 TeV vs. b*
S. Fartoukh, CM18/HiLumi-LHC meeting
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Typical settings [A] at 3.5 TeV for the sextupole families (Beam1) testing the ATS in the LHC
b*> 40 cm
10 cm < b*< 40 cm
During the telescopic part, the chromatic
correction is achieved by the b-beating!
 Only 25% of the RS circuits participates to the chromatic correction during the pre-squeeze
 All sextupole then kept ~ constant during the squeeze: THERE IS NO CHROMATIC LIMIT!
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
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