CryogenicCryogenic refrigerationrefrigeration for the LHCfor the LHC

Philippe Lebrun

CERN, Geneva, Switzerland

MaTeFu Spring Training School

Cadarache, 5-9 April 2009

The The largestlargest scientificscientific instrument in the worldinstrument in the world……

……basedbased on on advancedadvanced technologytechnology

23 km of 23 km of highhigh--fieldfield superconductingsuperconducting magnetsmagnets

operating in operating in superfluidsuperfluid heliumhelium atat 1.9 K1.9 K

SuperconductorsSuperconductors for for highhigh--fieldfield magnetsmagnets

0

500

1000

1500

2000

2500

3000

6 7 8 9 10 11 12

B [T]

Jc [A

/mm

2]

NbTi @ 4.5 KNbTi @ 1.8 KNb3Sn @ 4.5 KLHC Spec Cable 1LHC Spec Cable 2

+ 3 tesla

Cryogenic system layoutCryogenic system layout

• 5 cryogenic islands

• 8 cryogenic plants, each serving adjacent sector, interconnected when possible

• Cryogenic distribution line feeding each sector

Configuration of Configuration of cryogenicscryogenics atat LHC LHC eveneven pointpoint

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

Sha

ftS

urfa

ceC

aver

nT

unne

l

LHC Sector (3.3 km) LHC Sector (3.3 km)

1.8 KRefrigeration

Unit

New4.5 K

Refrigerator

Existing4.5 K

Refrigerator

1.8 KRefrigeration

Unit

WarmCompressor

Station

WarmCompressor

Station

WarmCompressor

Station

ColdCompressor

box

Even pointOdd point Odd point

MP StorageMP Storage MP Storage

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

Sha

ftS

urfa

ceC

aver

nT

unne

l

LHC Sector (3.3 km) LHC Sector (3.3 km)

1.8 KRefrigeration

Unit

New4.5 K

Refrigerator

Existing4.5 K

Refrigerator

1.8 KRefrigeration

Unit

WarmCompressor

Station

WarmCompressor

Station

WarmCompressor

Station

ColdCompressor

box

Even pointOdd point Odd point

MP StorageMP Storage MP Storage

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

UpperCold Box

Cold Box

WarmCompressor

Station

LowerCold Box

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

Sha

ftS

urfa

ceC

aver

nT

unne

l

LHC Sector (3.3 km) LHC Sector (3.3 km)

1.8 KRefrigeration

Unit

New4.5 K

Refrigerator

Existing4.5 K

Refrigerator

1.8 KRefrigeration

Unit

WarmCompressor

Station

WarmCompressor

Station

WarmCompressor

Station

ColdCompressor

box

Even pointOdd point Odd point

MP StorageMP Storage MP Storage

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

Magnet Cryostats, DFB, ACS Magnet Cryostats, DFB, ACS

ColdCompressor

box

Cryogenic plants Cryogenic plants

1.8 K refrigeration units(2.4 kW @ 1.8 K)

4.5 K refrigerators(18 kW @ 4.5 K)

Cryogenic storage and distributionCryogenic storage and distribution

GHe storage LIN storage

Cryo-magnet string Distribution line Interconnection box

Vertical transfer line

Analysis & management of heat loadsAnalysis & management of heat loads

• Heat inleaks

– Radiation 70 K shield, MLI

– Residual gas conduction Vacuum < 10-4 Pa

– Solid conduction Non-metallic supports Heat intercepts

• Joule heating

– Superconductor splices Resistance < a few nΩ• Beam-induced heating

– Synchrotron radiation

– Beam image currents 5-20 K beam screens

– Acceleration of photoelectrons

– Beam halo absorbed in cold mass

Analysis Management

SteadySteady--state heat loads [W/m]state heat loads [W/m]((CryomagnetsCryomagnets and distribution line in LHC arcs)and distribution line in LHC arcs)

* no contingency

0.110.424.607.7Total ultimate

0.110.401.827.7Total nominal

00.114.360Beam-induced ultimate**

00.091.580Beam-induced nominal**

00.100.0050.02Resistive heating

0.110.210.237.7Heat inleaks*

4 K VLP1.9 K LHe4.6-20 K50-75 KTemperature

3.070.89Photoelectron

0.050.05Beam-gas Scattering

0.820.36Image current

0.500.33Synchrotron radiation

ultimatenominal** Breakdown

ScalingScaling lawslaws for LHC for LHC dynamicdynamic loadsloads

UncertaintyUncertainty & & overcapacityovercapacity factorsfactors

• Uncertainty factor Fin– Lack of reproducibility in construction (e.g. MLI wraps)

– Variance of thermal processes at work (e.g. insulation vacuum)

– Evolution in time (ageing, contamination of reflective surfaces)

⇒ applied to static loads only, dynamic loads and their scaling known

from first principles

• Overcapacity factor Foc– Cooldown in finite time

– Refrigerator loading < 100 %

– Variability of machine performance

⇒ applied to sum of static load with uncertainty and dynamic load

⇒ no overcapacity applied to ultimate conditions

OverallOverall factor on factor on installedinstalled refrigerationrefrigeration

• Installed refrigeration power

Qinstalled = Max [Foc (Fin Qstat + Qdyn nom); (Fin Qstat + Qdyn ult)]

• Values of uncertainty & overcapacity factors

– Fin = 1,5 at beginning of project

– Foc= 1,5

– Fin gradually lowered following refinement of project configuration and improved knowledge of component thermal performance

Evolution of estimated heat loads & installed Evolution of estimated heat loads & installed

refrigeration capacity per LHC sectorrefrigeration capacity per LHC sector

0

10

20

30

40

50

YR 1987

PB 1991

WB 1993

YB 1995

Specif. 1997

Rev. 2000

As built

Hea

t loa

d @

50-

75 K

[kW

] Static Total Installed

0

2000

4000

6000

8000

10000

YR 1987

PB 1991

WB 1993

YB 1995

Specif. 1997

Rev. 2000

As built

Hea

t loa

d @

5-2

0 K

[W] Static Total Installed

0

1000

2000

3000

YR 1987

PB 1991

WB 1993

YB 1995

Specif. 1997

Rev. 2000

As built

Hea

t loa

d @

1.9

K [W

] Static Total Installed

0

10

20

30

40

50

60

YR 1987

PB 1991

WB 1993

YB 1995

Specif. 1997

Rev. 2000

As built

CL c

oolin

g [g

/s]

Static Total Installed

Installed cooling duties in the LHC sectorsInstalled cooling duties in the LHC sectors

[g/s]274120-280 K

[W]3804303-4 K

[W]210024001.8 K

[W]1503004.5 K

[W]760077004.6-20 K

[W]310003300050-75 K

Low-load sectorHigh-load sectorTemperature

level

Evolution of installed power to heat load ratioEvolution of installed power to heat load ratio

1

1.5

2

2.5

3

YR1987

PB1991

WB1993

YB1995

Specif.1997

Rev.2000

Asbuilt

Capa

city

rat

io [

-]

50-75 K 5-20 K 1.9 K CL cooling

Overcapacity target

Procurement from industryProcurement from industry

• European industry (Air Liquide & Linde Kryotechnik) had demonstrated their competency and know-how in manufacturing turnkey helium refrigerators of medium or large capacity

– HERA (10 kW)

– LEP2 (6 kW, 12 kW)

• Most efficient approach was therefore to procure via a functional and interface specification

– Transform sector cooling requirements into refrigeration duties which can be reception-tested at cryoplant interface

– Clearly define interfaces to cryogenic and other systems

– Promote energy-efficient solutions

• Oligopolistic nature of market & desire to balance industrial returns among Member States led to split procurement under constraints

– Align prices to satisfy CERN lowest-bidder purchasing rule

– Impose convergence of non- or less-proprietary part of supply, i.e. compressor station and control system

Conversion of Conversion of coolingcooling dutiesduties

fromfrom LHC LHC sectorsector to 4.5 K to 4.5 K refrigeratorrefrigerator

Specified refrigeration capacitySpecified refrigeration capacity

for the LHC 4.5 K refrigeratorsfor the LHC 4.5 K refrigerators

41

4400

20700

33000

Newrefrigerator

27

4150

19500

31000

Upgradedrefrigerator

[g/s]20-280 K

[W]4.5 K

[W]4.5-20 K

[W]50-75 K

UnitTemperature level

ScalingScaling lawslaws for for costcost of of cryogeniccryogenic He He refrigeratorsrefrigerators

(single cold box, no LIN (single cold box, no LIN precoolingprecooling, , controlscontrols excludedexcluded))

How to specify an efficient He refrigeratorHow to specify an efficient He refrigerator

• Include capital & operating costs over amortization period (10 years)in adjudication formula

• Operating costs dominated by electricity

• Include externalities in electricity costs => 60 CHF/MWh– distribution & transformation on CERN site

– heat rejection in aero-refrigerants

• Establish shared incentive in the form of bonus/malus on measured vs. quoted electrical consumption

• Break “high efficiency = high investment” pseudo-rule: for given (specified) output, a more efficient plant is smaller, resulting in lower investment (direct & indirect) as well as cheaper operation

How to How to makemake an efficient an efficient refrigeratorrefrigerator(exemplified on (exemplified on Carnot cycle Carnot cycle schematicschematic))

Tw

Tc

T

S

T

S

Tw

Tc

isentropicadiabatic

Cooling power

Widen the low-temperature end of the cycle as shown in the T-S diagram

Work Work

Ideal Real

∆S1 ∆S2

AB

C D

AB

C D

T54.5 K - 20 K loads

(magnets + leads + cavities)

T7

T1

T2

T3

T4

T8

T6

E1

E7

E3

E4

E6

E8

E9a

E9b

E10

E11

E12

E13

LN2Precooler

20 K - 280 K loads

(LHC current leads)

50 K - 75 K loads

(LHC shields)

Adsorber

T1

T3

T7

T4

T8

T5

T6

201 K

75 K

49 K

32 K

20 K

13 K10 K

9 K

4.4 K

0.1 M

Pa

0.4 M

Pa

1.9 M

Pa

0.3 M

Pa

T2

LHC shields

To LHC loads

from LHC loads

from LHC loads

ProcessProcess cycle & Tcycle & T--S S diagramdiagram

of 18 kW @ 4.5 K of 18 kW @ 4.5 K cryoplantcryoplant

Compressor station of 4.5 K refrigeratorCompressor station of 4.5 K refrigerator

ORSHP supply

MP return

LP return

LP compressors

HP compressors

Oil removal system

Gas coolers

800 g/s @ 1.05 bar

880 g/s @ 3.9 bar

1680 g/s @ 20 bar

Electrical power consumption: 4 MW

Identical installation for both suppliers

Compressor station of 4.5 K refrigeratorCompressor station of 4.5 K refrigerator

(Power input ~ 4 MW)(Power input ~ 4 MW)

Cold box of Air Cold box of Air LiquideLiquide 4.5 K refrigerator4.5 K refrigerator

HP

MP

LP

300 K 75 K 50 K 20 K

4.5 K supply

20 K return

75 K return

50 K supply

4.5 K

Cold box of Air Cold box of Air LiquideLiquide 4.5 K refrigerator4.5 K refrigerator

Cold box of Cold box of LindeLinde 4.5 K refrigerator4.5 K refrigerator

4.5 K supply

20 K return

50 K supply

75 K return

HP

MP

LP

300 K 90 K 75 K 50 K 20 K 4.5 K

Cold box of Cold box of LindeLinde 4.5 K refrigerator4.5 K refrigerator

Guaranteed Guaranteed vsvs measured performancemeasured performance

of the new LHC 4.5 K refrigerators of the new LHC 4.5 K refrigerators

231222247248COP [W/W]

99.3100.1101.597.3Measured cryogenic capacity[% of specified]

4095396444744297Measured energy consumption [kW]

4275427542044204Guaranteed energy consumption [kW]

LindeLindeAir LiquideAir LiquideSupplier

PA8PA6PA4PA18LHC location

C.O.P. of large C.O.P. of large cryogeniccryogenic heliumhelium refrigeratorsrefrigerators

0

100

200

300

400

500

TORESUPRA

RHIC TRISTAN CEBAF HERA LEP LHC

C.O

.P. [

W/W

@ 4

.5K

]

Carnot Limit

Liquid nitrogen Liquid nitrogen precoolingprecooling

• Each 3.3 km sector has a mass of 4625 t to be cooled in few weeks

• Corresponding power 600 kW, must be generated by vaporization of 1250 t LIN at rates of up to 5 t/h

• LIN precooling not foreseen for steady-state operation, but may alsobe used to boost helium liquefaction

First First cooldowncooldown of LHC of LHC sectorssectors

Challenges of power Challenges of power refrigerationrefrigeration < 2 K< 2 K

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssur

e [k

Pa]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II(Subcooled liquid)

SATURATED He II

SUPER-CRITICAL

SATURATED He I

Compression > 80

• Compress large mass-flow rate of gaseous helium across high pressure ratio

⇒ maximum density at suction, i.e. cold

• Non-lubricated, contact-less machinery ⇒ hydrodynamic compressor, multistage

• Heat of compression rejected at low temperature ⇒ high thermodynamic efficiency

Main Features of LHC Cold CompressorsMain Features of LHC Cold Compressors

Axial-centrifugalimpeller (3D)

Fixed-vanediffuser

3-phase inductionelectrical motor(rotational speed 200 to 700 Hz)

Activemagneticbearings

300 K under

atmosphere

Cold under

vacuum

Inlet

Outlet

Pressure ratio2 to 3.5

Spiral volute

Cold Cold hydrodynamichydrodynamic compressorscompressors for the LHCfor the LHC

IHI-Linde Air Liquide

Specification of LHC 1.8 K refrigeration unitsSpecification of LHC 1.8 K refrigeration units

Steady state operation modes:– Installed pumping capacity 125 g/s at 15 mbar(i.e. ~2.4 kW @ 1.8 K)

– Turndown capability: 1 to 3 without extra liquid burning

– Cold return temperature to the 4.5 K refrigerator below 30 K (reduced capacity) to 20 K (installed capacity).

– Capacity check in standalone mode (Interface B closed)

0.3 MPa4.6 K

0.13 MPa,20 -30 K

WC

S

1.8

K R

efri

gera

tion

Un

it

LHe 1.8 K Q1.8K

CC

B

4.5 KRefrigerator

B

D

C

Col

d co

mpr

esso

rs

Tur

blne

Adsor-bers

LHC SectorLoad

1.8 K 1.8 K refrigerationrefrigeration cycles for the LHCcycles for the LHC

1.8 K Refrigeration Unit Cycles

CC

Hea

tIn

terc

epts

Air Liquide Cycle IHI-Linde Cycle

4 K, 15 mbar124 g/s

20 K, 1.3 bar124 g/s

0.35 bar

4.75 bar

4 K, 15 mbar124 g/s

20 K, 1.3 bar124 g/s

0.59 bar

9.4 bar

4.6 bar

CC

CC

CC

CC

CC

CC

CC

T

T

T

Adsorber

Adsorber

WC

WC

WC WC

HX

HX

HX

HX

Isentropic efficiency of cold compressorsIsentropic efficiency of cold compressors

0

10

20

30

40

50

60

70

80

1985 1993 2000Year of construction

Isen

trop

ic e

ffici

ency

[%]

Tore Supra

CEBAF

LHC

12

12'is HH

HHη

−−=

Temper

atur

e (T

)

Entropy (s)

P1

P2

1

2

2'

C.O.P. of LHC 1.8 K refrigeration unitsC.O.P. of LHC 1.8 K refrigeration units

0

200

400

600

800

1000

Air Liquide IHI-Linde

CO

P [W

@R

T /

W@

1.8K

]4.5 K refrigerator part 1.8 K refrigeration unit part

Carnot Limit

Controls for LHC cryogenicsControls for LHC cryogenicsChallenges & solutionsChallenges & solutions

UNICOS framework providing1. Programmable logic controllers (PLC) and associated hardware2. Programming rules and code library for common objects3. Automated tools for writing control code4. Gateways based in industrial PC for WorldFIP-based signal conditioners5. Communication via Ethernet gateways <-> PLC and PLC <-> PLC6. Event-driven communication protocol between PLC <-> SCADA7. SCADA based in PVSS with generic widgets, look-and-feel and shared data

server

4704481003285483680Closed Loop Controllers

421227223211849561568Digital Outputs

183565921144398481004536Digital Inputs

700811229260811404856Analog Outputs

2133621611282640521612136Analog Inputs

TOTALCommonQUI1.8 K units4.5 K

refrigeratorsTunnel

Control system architectureControl system architecture

• Field layer- Interface to process direct

I/O Boards, Fieldbuses

• Process control layer- PLC : the control logic is

performed at that level- Programmers act on that

Level

• Supervision layer- Interface for operation team - All operators action are

taken from this level

OperatorOperator--friendlyfriendly SCADASCADA

Animatedsynoptics

Alarm & event lists

PID controllers

Trend charts

SomeSome referencesreferences

• Ph. Lebrun, Cryogenics for the Large Hadron Collider, IEEE Trans. Appl. Superconductivity 10 (March 2000) 1500-1506

• S. Claudet, P. Gayet & U. Wagner, Specification of four new large 4.5 K helium refrigeration systems for the LHC, Adv. Cryo. Eng. 45B (2000) 1269-1276

• S. Claudet, P. Gayet, B. Jager, F. Millet, P. Roussel, L. Tavian & U. Wagner, Specification of eight 2400 W @ 1.8 K refrigeration units for the LHC, Proc. ICEC18 Mumbai, Narosa (2000) 207-210

• Ph. Lebrun, Large cryogenic refrigeration system for the LHC, Proc. ICCR’2003 Hangzhou, IIR (2003)

• H. Gruehagen & U. Wagner, Measured performance of four new 18 kW @ 4.5 K helium refrigerators for the LHC, Proc. ICEC20 Beijing, Elsevier (2005) 991-994

• L. Serio et al., Validation and performance of the LHC cryogenic system through commissioning of the first sector, Adv. Cryo. Eng. 53B (2008) 1411-1418

• S. Claudet, Ph. Lebrun, L. Serio, L.Tavian, R. van Weelderen & U. Wagner, Cryogenic heat load and refrigeration capacity management at the Large Hadron Collider, presented at ICEC22 Seoul (2008)