for the 100 TeV Future Circular Collider (FCC-hh)
Herman ten Kate
C.Berriaud, B.Cure, A.Dudarev, A.Gaddi, H.Gerwig, M.Mentink, G.Rolando, H.Silva, U.Wagner, S.Klyukhin
1. Present LHC and future FCC
2. Physics requirements and design drivers
3. Magnet system layout options
4. Cost scaling
5. Twin Solenoids design
6. Installation challenges
7. Conclusion
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13-14 TeV p-p LHC
H -> ZZ -> 4 μ with m
4 μ
= 124.6 GeV
2

Energy = 0.3 x B x R
B: 1.9 x from NbTi to Nb
3
Sn
B: 2.4 x from NbTi to HTS
R: 4-5 x more magnets
≈ 15 T ⇒ 100 TeV in 107 km
≈ 16 T ⇒ 100 TeV in 100 km
≈ 20 T ⇒ 100 TeV in 80 km
•
New ≈100 km tunnel in
Geneva area
•
100 TeV p-p determines the size
•
Options for adding an e+e collider (TLEP) & pe collider (VLHeC)
•
New CERN-hosted study started in Feb 2014.
• An extremely challenging project.
 The options shall be explored……
LHC
100 TeV p-p FCC
Detectors in 350 400 m deep caverns !
3

Charged by European Strategy Update on HEF: “CERN should undertake design studies for accelerator projects in a global context, with emphasis on
proton-proton and electron- positron high-energy frontier machines.” today
Possible FCC
1 st step in progress:
FCC
Study
FCC Study: a p-p machine to achieve 100 TeV, CDR & Cost Review in 2018
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What determines the size of the detectors:
 Bending power in inner tracker and muon system :
•
7 x higher collision energy, 14 > 100 TeV, but keeping tracking resolution
•
Sagitta of charged particles in magnetic field B across length L: ∝ B.L
2
• and momentum resolution ∝ σ /BL 2
---> BL 2 / 𝝈𝝈 to be increased by a factor 7 !
 Combination of a higher point resolution, higher field and increase of radius;
 Radius is most effective!
For detector solenoids this means:
---> Scale up magnetic field from 3.5 up to 5 or 6 T and increase bore size!
5

 Calorimeters need minimum depth to stop all particles except muons.
--> Increase radial thickness from 10 to 12 λ !
•
Based on steel absorbers:
0.6 m deep ECAL + 2.2 m deep HCAL, makes a total radial build-up of 3.4 m.
--> For an inner tracker diameter of 3, 4 or 5 m (depending on field and tracker point resolution) , the bore of the solenoid or toroid becomes 10.0 to 12.0 m!
What determines the length of the system:
 Coverage in forward direction, in center of magnet up to 23°
Length of solenoid is 3.84xR , L=R/tan (23°): 10 m bore, means 19 m long,
12 m bore, means 23 m long.
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 Extra forward tracker and calorimeter to cover low angles
•
Move unit out, from 5 to ≈ 15 m, thus the system gets longer!
 Low angle coverage up to 7.7° (ɳ>2.7) with 10 Tm in forward direction
 Overall detector length 60 80m!
•
High field toroid difficult, all current has to pass the small inner bore.
•
Solenoid is an option (extension of main solenoid, tracking over entire length).
•
A dipole for on-beam bending featuring 10 Tm.
 Note: maximum system sizes presented here for best physics performance, for cost or technical reasons size and field may be scaled down a bit later on in the process……
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50 60 m
 Solenoid: 10 -12 m diameter, 19-23 m long, and 5-6 T
+ iron yoke for flux shielding and muon tracking.
 Dipoles: 10 Tm with return yoke placed at z≈18 m.
Practically no coupling between dipoles and solenoid.
They can be designed independently at first.
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Example: 6 T, 12 m bore, 23 m long, 28 m OD
•
Stored energy 54 GJ, 6.3 T peak magnetic field.
Yoke? Thickness depends on use of the yoke:
•
For 100% shielding we need 6.3 m thick iron for a 10 mT stray field line at 22 m
≈15 m 3 , mass ≈ 120 kt (≈ 600 M € !).
Huge mass, serious consequences for cavern floor, installation, not elegant.
•
For simple muon tagging at 4 Tm, yoke thickness can be limited to 3 m, still 60 kt
•
Even more simpler muon tagging at 1 Tm, yoke thickness 1 m, still 22 kt
Solenoid with 1 m iron,
43 GJ, 30 kt total mass
•
Stray field: with 2 layers, 1 m iron, 22 kt iron: 14 mT at 50 m, 300 mT at 30 m.
•
When not fully shielding, the fringe field has to be made acceptable, or in critical areas be reduced by local iron shielding or active compensation.
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shielding coil Gap filled with 3 T and muon chambers
Twin Solenoid: 6 T, 12 m free bore, 23 m long main solenoid + shielding coil
I mportant advantages:
•
Nice muon tracking space: gap with ≈ 2 -3 T for muon tracking in 4-5 layers.
•
Light: shielding coil + structure ≈ 6 -8 kt , much lighter than the iron yoke!
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Example: 6 T in 12 m bore, 23 m long:
•
2 to 4 T in gap depending on gap size, to be tuned.
•
≈2 T in a 6 m gap or ≈2 -4 T in a 3-6 m gap.
•
Many ways to adjust outer coil to specific requests.
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Superconducting coils Support structure 15
10
5
-16 -12 -8 -4 0 4 8 12 16
0
•
Stored energy 54 GJ, conductor stored energy density: 12 kJ/kg.
•
6.0 T in center, 6.4 T peak field in turns, conductor 4 kt, cold mass: ≈ 6 kt.
•
Large forces resulting from minor misalignments between the coils, but doable!
•
Support cylinders and spokes are critical parts of the cold mass.
•
2.6 T in 3.5 m gap between solenoids for muon trackers.
•
5 mT line at 28 meters radius.
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3.5 T Central Solenoid for the inner detector trackers (0.6 GJ).
- One Air core Barrel Toroid with 16 Tm in toroid window (48 GJ).
Two End Cap Toroids to cover medium angle forward direction (2 x 1.6 GJ).
Two internal Dipoles to cover lowangle forward direction with 10 Tm.
- Large s ize: 30 m diameter x 52 m length (36,000 m 3 ) .
- Least popular option, stand-alone muon tracker in toroid not so much needed.
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Effect of B and R ∝ L on Solenoid Cost:
•
Following scaling rules, calibrated with
LEP & LHC detector magnets.
•
Cost of 4, 5 and 6 T solenoids (no yoke) with radii of 3.5 to 6 m, length follows for fixed 28° opening angle.
•
Same when including a minimum yoke
(based on 4 M€/kt all-in).
 Example: 6 T is ̴60 % more expensive in a 12 m bore than in a 10 m bore……!
Disclaimer: preliminary estimate for such large systems !
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Cost of a standalone helium plant
He plant cost ≈ 1.2 x 2.6 x P(kW@4K) 0.6
[in 2015 M €]
(1.2 amplification factor for auxiliaries, transfer lines; 2.6 is a constant accounting for inflation)
Cryogenics power scales with surface of cryostat, 1 in single solenoid, 2 in twin solenoid 2 and many in toroids.
Example for solenoid scaling:
•
CMS-Solenoid today has 1.5 kW.
•
Solenoid-Yoke in R=6m/L=23m version needs 4.5x, so 7 kW (9 M€).
•
Twin Solenoid in R=6m/L=23m requires 12x, so 18 kW (18 M€).
•
Why? 2 cryostats and more surface on the shielding coil !
Cryogenics cost are in the 10 20 M€ range and small compared to cost of magnets and iron.
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FCC air core Twin Solenoid and Dipoles.
State of the art high stress & low mass design.
Stored energy
Total mass
Peak field
Current
Conductor
Bore x Length
Twin Solenoid Dipole
53 GJ 2 x 1.5 GJ
7 kt
6.5 T
80 kA
102 km
12 m x 20 m
0.5 kt
6.0 T
20 kA
2 x 37 km
6 m x 6 m
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Twin Solenoid:
Spokes
Twin Solenoid:
Inner solenoid
Dipole lateral coils
Dipole main coils
Force and torque neutral dipole
Property
TS cold mass
Value
3.2 kt
TS vacuum vessel mass 2.4 kt
TS stored energy
Dipoles cold mass
Dipoles stored energy
Free bore
Outer diameter
System length
Total stored energy
53 GJ
2x 380 t
2x 1.5 GJ
12 m
27 m
42 m
56 GJ
Twin Solenoid: Shielding outer solenoid
•
Full angle coverage: Twin Solenoid for high angle particles, dipoles for low angle particles
•
Force & Torque neutral twin solenoid through cold spokes, force & torque neutral dipoles through lateral compensation coils
•
Shielding? 5mT boundary is at R
Z=0
= 32 m, R
Widest
= 35 m, Z
R=0
= 57 m
17

•
Magnetic field lines in vertical YZ plane
•
Dipole polarity: right-up & left-down configuration
18

Depth where new tunnel is routed: Detectors in points A-F-G-H: 300 - 400 m below surface!
≈28m
≈ 67x35x38 ≈ 90000 m 3
•
Installation scenario’s needed for all variants, a 400 m deep shaft is not easy!
•
On-surface whole coil, 2-3 kt units descending through 28 m shaft?
•
Or production of lighter modules and do in-cavern assembly ? Many questions.
19

 Conceptual design study for Detector Magnets at the Future Circular Collider in progress.
 A first look at options for magnet systems probing 100 TeV p -p collisions completed.
 Magnet system size grows with collision energy.
 Magnet systems are “huge”: 20 30 m diameter, 30 50 m long, 50 60 GJ.
 Main focus is on 2 designs featuring 6 T in 12 m free bore
‒ Twin Solenoid has nice features: light, elegant, effective shielding, and allowing high-quality muon tracking in the intervening space.
‒ Solenoid + light Yoke , heavy, even with minimum yoke, partly shielded only.
‒ Including innovative 10 Tm dipoles for covering forward physics.
The good news: there are no principle technical problems impeding the constructing of these magnets.
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