The Future Circular Collider (FCC) project and its cryogenic challenges

Laurent Tavian, CERN ECD 2017, Karlsruhe, 13 September 2017 Content

• Introduction: Scope of the FCC study

• FCC-hh tunnel cryogenics and user heat loads

• FCC-hh cryogenics layout and architecture

• FCC-hh cool-down and nominal operation

• FCC-hh electrical consumption and helium inventory

• Conclusion Scope of FCC Study

International FCC collaboration (CERN as host lab) to study: • pp-collider (FCC-hh)  main emphasis, defining infrastructure requirements ~16 T ⇒ 100 TeV pp in 100 km • ~100 km tunnel infrastructure in Geneva area, site specific • e+e- collider (FCC-ee), as potential first step • p-e (FCC-he) option, integration one IP, e from ERL • HE-LHC with FCC-hh technology • CDR for end 2018 Luminosity vs energy of colliders

Conventional He I He II 1.E+36 x 7 FCC

1.E+35 HL-LHC

] x 30 1

- LHC 2017 .s

2 1.E+34

- LHC (design)

1.E+33

ISR 1.E+32 LEP2 HERA TeVatron Luminosity [cm LEP1 1.E+31 SppS

1.E+30 0.01 0.1 1 10 100 Centr-of-mass energy [TeV] CERN Collider plan

1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040

Construction Physics Upgr LEP

Design Proto Construction Physics LHC

Design Construction Physics HL-LHC

Future Collider Design Proto Construction Physics

~25 years FCC-hh baseline parameters

Parameter LHC HL-LHC FCC-hh c.m. energy [TeV] 14 100 Nb3Sn superconducting dipole magnet field [T] 8.33 16 magnets cooled at 1.9 K circumference [km] 26.7 100 luminosity [1034 cm-2.s-1] 1 5 5 29 bunch spacing [ns] 25 25 event / bunch crossing 27 135 170 ~50 mm bunch population [1011] 1.15 2.2 1 norm. transverse emittance [µm] 3.75 2.5 2.2 IP beta-function [m] 0.55 0.15 1.1 IP beam size [µm] 16.7 7.1 6.8 synchrotron rad. [W/m/aperture] 0.17 0.33 28 critical energy [keV] 0.044 4.3 5 MW dissipated in cryogenic environment total syn. rad. power [MW] 0.0072 0.0146 4.8  beam screens are mandatory longitudinal damping time [h] 12.9 0.54  Cooling temperature 40-60 K Magnet cooling cost including 10 years of operation

1

He II cooling Min Max [a.u.] Magnet cooling at 1.9 K vs 4.5 K: About a factor 2 on the magnet 0.5 cooling cost largely compensated by the saving on superconducting material  Tmagnet = 1.9 K He I cooling FCC magnet cooling cost cost cooling magnet FCC

0 1.5 2 2.5 3 3.5 4 4.5 5 Magnet temperature [K] Beam screen – cold mass thermodynamics

Cold bore (Tcm)

Ta: Ambient temperature Qbs Cooling channel (Tbs)

Support Qcm Qsr Energy balance: beam Qbs = Qsr - Qcm Beam screen (Tbs)

- Exergy load ∆E = measure of (ideal) refrigeration duty :

∆E = ∆Ecm + ∆Ebs ∆E = Qcm . (Ta/Tcm – 1) + Qbs . (Ta/Tbs – 1)

- Real electrical power to refrigerator: Pref= ∆E/η(T) with η(T) = efficiency w.r. to Carnot = COPCarnot/COPReal Pref = Qcm . (Ta/Tcm – 1)/η(Tcm) + Qbs . (Ta/Tbs – 1)/η(Tbs) BS – CM thermodynamics Numerical application

3000 Total electrical power to refrigerator Pref. considering: 2500 - a beam screen similar to that of the LHC - refrigerator efficiencies identical to those 2000 of the LHC. 1500

Optimum for Tbs= ~ 70 K 1000

500

Temperature range 40-60 K retained per beam] [W/m to refrigerator power Total 0 0 50 100 150 200

Beam-screen temperature, Tbs [K]

Forbidden by vacuum and/or by surface impedance FCC-hh: tunnel cryogenics

Main distribution based on INVAR® technology Contribution of WUST Specific heat loads at different temperature levels

Temperature level 40-60 K 1.9 K 4 K VLP CM supporting system 2 0.13 Radiative insulation 0.13 Thermal shield 3.1 Static heat in-leaks Feedthrough & vacuum barrier 0.2 0.1 [W/m] Beam screen 0.12 Distribution 4 0.1 0.24 Total static 9.3 0.58 0.24 Synchrotron radiation 57 0.08 Image current 3.4 Dynamic heat loads Resistive heating in splices 0.3 [W/m] Beam-gas scattering 0.45 Total dynamic 60 0.83 Total [W/m] 70 1.4 0.24 Dynamic range [-] 8 2.5 1 FCC-hh cryogenic layout and architecture

40-60 K 1.9 K 4 K VLP 40-300 K [kW] [kW] [kW] [g/s] 580 12* 2 85 Without operational margins as the working conditions has to be considered as ultimate *: Outside State-of-the-Art State-of-the-art of cold compressors (single train)

12 FCC-hh

10

8 Increase by a factor 5 on the cooling power, i.e with respect to the present technology: 6  Impeller diameter from 350 mm to 700 mm (factor 2) 4 LHC  Shaft power from 10 kW to 30 kW (factor 3)

Total cooling Total cooling power [kW] 2

0 1.6 1.7 1.8 1.9 2 2.1 Saturated temperature [K] FCC-hh cryoplant architecture

C C C C C C Quench buffer

• Beam screen (40-60 K) Ne-He T • Thermal shield (40-60 K) 300-40 K • Current leads (40-300 K) C • Precooling of 1.9 K cryoplant T cryoplant Surface

LHe storage

Shaft

T Cavern

He 1.8 K • SC magnet cold mass T cryoplant T

Tunnel E F C Qb B D Qts Qcl Qcm Contributions of TU Dresden and CEA/SBT CM Qbs Qts Ne-He cycle: 750-1000 kW between 40 and 60 K

C

Hermetically sealed centrifugal compressors: - No dry gas seals, no lube-oil system and no gearbox Turbo- - Use of high speed induction motor (up to 200 Hz) T Brayton and active magnetic bearings. The motor is cooled by cycle process gas and directly coupled to the barrel type Courtesy of MAN Diesel & Turbo compressor.

C T Difficult to get high compression ratio and high compression efficiency with pure helium (light mono-atomic gas):  Compression of a mixture of helium and neon (~75-25 %) (OK with neon as refrigeration T > 40 K)  The warm compression efficiency is improved  Expected global efficiency with respect to Carnot  42 %

Cryogenics (CERN), L. Tavian, 1st Sept’17 Cooldown of FCC-hh

C C C C C C Quench He cycle buffer Cool-down capacity produced Ne-He cycle by the Ne-He cycle:

No need of LN2 cool-down T unit with its huge LN2 storage and logistics

C T Cold mass: 2.8 t/m i.e. Surface 23 kt per sector LHe storage 230 kt for FCC Shaft T Cavern

15 days of cool-down time T from 300 to 40 K (10 days (on paper) with LN2). T 50 bar supply pressure Cost (only energy)  indirect cool-

Qb down of cold- Full FCC CD  2.3 MCHF Tunnel E F C B D masses (design

(To be compared with the Qts pressure of 20 Qcl cost of a CD using LN2  Qcm bar) CM 45000 t, i.e. ~4 MCHF) Qbs Qts FCC-hh Nominal operation

C C C C C C Quench C C C C C C Quench buffer He cycle buffer Ne-He cycle

T T

C C T BS cooling with cold circulator (+130 kW @ 40-60 K) T Surface Exegetic efficiency of BS cooling loop: 82 % Surface

LHe storage LHe storage

Shaft Shaft T BS cooling with warm circulator needed for cooldown T Cavern Cavern (+140 kW @ 40-60 K and +500 kW @ 300 K)  T Less efficient (exergetic efficiency of 71 %) but good for T redundancy. T T Qb Tunnel E F C B D Tunnel E F C Qb B D 1.8 K refrigeration based on a mixed compression Qts cycle (cold centrifugal compressors in series with Qts Qcl Qcl Qcm warm volumetric compressors) Qcm CM CM Qbs Qts Qbs Qts FCC-hh Half-cell cooling loop

Line B (4 K, 15 mbar) Line C (4.6 K, 3 bar) Line D (40 K, 1.3 bar) Line E (40 K, 50 bar) Line F (60 K, 44 bar)

V2 Sub-cooling HX Distribution-line thermal shields V4 Bayonet HX V7 Feeder pipe V3 V6 V5 V1 Magnet thermal shields and support-post heat intercepts

Beam 1

Beam 2

Q D D D D D D

SC coils Beam screens Pressurized LHeII Half-cell length (~107 m) FCC-hh Superfluid helium cooling loop parameters

Variable Unit LHC FCC Unit cooling length m 106.9 107.1 Sector cooling length m 2900 8400 Average heat load nominal capacity W/m 0.40 1.38 Bayonet HX inner diameter mm 53.4 83.1 Feeder pipe inner diameter mm 10.0 15.0 Thickness bayonet HX pipe wall mm 2.3 5.0 Joule-Thomson valve inlet temperature K 2.18 2.18 Free longitudinal cross-section area cm2 60 156 DT max Pressurized-saturated HeII mK 50 50 Cold mass operating pressure bar 1.3 1.3 Header B diameter mm 270 630 (500) Heat load on header B W/m 0.11 0.24 Pumping pressure at cryoplant interface mbar 15 15 Maximum cold-mass helium temperature K 1.9 1.9 (1.98) FCC-hh Beam-screen cooling loop parameters

Main parameter Unit LHC FCC Transient modes Unit cooling length m 53.4 107.1 Sector cooling length m 2900 8400 - Working at constant nominal mass-flow to Average BS nominal capacity W/m 1.6 60 handle the severe transient during energy ramp-up Max. supply pressure bar 3 50 - Working at constant He Supply helium temperature K 5 40 inventory to avoid big mass discharge and refill (~6 t) Max. allowed BS temperature K 20 60 (i.e. pressure increase BS helium outlet temperature (nominal) K 20 57 during energy ramp) Minimum BS temperature (nominal) K 5 43 Large inertia of the distribution system BS pressure drop (nominal) bar 0.5 3  time constant of~ 4 h ∆P control valve (nominal) bar 0.8 1  OK with the capacity adaptation of the ∆P supply and return header (nominal) bar 0.4 2 cryoplants Total cooling loop pressure drop bar 1.7 6  In high luminosity operation (4 h of stable Supply/return header diameter mm 100/150 250/250 beams), the cryoplants will Exergetic efficiency (distribution only) % 76 86 be never in steady-state Total exergetic eff. (with cold circulator) % N/A 82 Total exergetic eff. (with warm circulator) % ? 71 FCC-hh electrical consumption

200 RH: resistive heating RH BGS: beam-gas scattering 180 BS: beam screen 160 BGS CM: cold mass heat-inleaks CL: current lead 140 BS BS cir.: Beam screen circulator (warm) TS: thermal shield CM 120 1.9 K IC: image current 100 CL 40-300 K SR: synchrotron radiation [MW] BS Cir. 80 40-60 K Carnot efficiency: TS - Ne-He plants: 40 % IC 60 - Helium plants: 28.8 % hh hh electrical power to refrigerator - 40 SR Isentropic efficiency FCC 20 - cold compressors: 75 % per stage - Warm circulator: 83 % 0 FCC-hh He inventory

Cold mass He inventory : 33 l/m (scaled from LHC) Distribution inventory dominated by the beam-screen supply and return headers

1000 Inventory breakdown FCC 800 100% 600 80% 60% 400 40% 200 20% LHC hh He [ton]inventory - 0 0% LHC FCC FCC 0 5000 10000 Distribution length [m] CM Distribution

Distribution Cold-mass Total FCC He inventory: ~800 t ! (~6 LHC He inventory) FCC-hh Storage management

L A B GHe storage - 60 (250 m3, 20 bar) Quench buffer - 156 (250 m3, 20 bar) K C GHe storage - 10 (250 m3, 50 bar) Ne-He storage - 10 (250 m3, 50 bar) He storage capacity: GNe cylinders - 10 (10 m3, 200 bar) GHe: 190 t LHe storage - 50 (120 m3) LHe: 650 t Total: 840 t LHe boil-off liquefier - 6 (150 to 300 l/h) J D LN2 storage - 6 (50 m3)

I E

H G F Main FCC cryogenics challenges: Cryogenic power

1200

1000 FCC-hh Today 800 ? 600

kW kW @ K 4.5 LHC FCC-ee 400 ATLAS, CMS ALEPH, DELPHI, LEP Low-Beta History 200 OMEGA, BEBC LEP2 HL-LHC ISR Low-Beta FCC 0 1940 1960 1980 2000 2020 2040 2060 2080 Year

Cryogenics (CERN), L. Tavian, 1st Sept’17 Conclusion

• The conceptual design of the cryogenic systems for a Future Circular Collider is in progress in the framework of an international collaboration (CEA, CERN, TUD, WUST) • The final Conceptual Design Report (CDR) will be issued by 2018 and then examined by the next European Strategy for high energy particle physics. • In the case of a positive feedback, the next step will be the studies and developments of the new concepts with the construction of demonstrators and/or prototypes.