HL-LHC optics S. Fartoukh, CERN-BE-ABP
Download
Report
Transcript HL-LHC optics S. Fartoukh, CERN-BE-ABP
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
2
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
3
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
4
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
7
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
9
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
10
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
11
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
12
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)
14
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)
15
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 (IR4IR6)
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)
16
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
17
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
140150 (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
140150 (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)
21
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
22
... Reserve
07/05/2012
S. Fartoukh, CM18/HiLumi-LHC meeting
23
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
24
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
25