cryogenics for the large hadron collider (lhc): design ......easitrain school 2, cea saclay 1st...

Cryogenics for the Large Hadron Collider (LHC):design, construction, operation & upgrade

Philippe LebrunCERN retired

EASITrain School 2, CEA Saclay

1st October 2019

http://doc.cern.ch/archive/electronic/cern/others/PHO/photo-bul/bul-pho-2007-046_01.jpg

Contents

• Technical challenges of the LHC

• He II magnet cooling scheme

• Cryostat design and heat loads

• Refrigeration at 4.5 K and 1.8 K

• Specific He II technologies

• Instrumentation and controls

• Operation

• Upgrade


Superconductivity and cryogenics are key technologies to the LHC and its large, multipurpose detectors


A new territory in energy and luminosity

ISR

SppS

TeVatron

LEP1

LEP2 HERA

LHC

1.E+30

1.E+31

1.E+32

1.E+33

1.E+34

1.E+35

10 100 1000 10000 100000

Lu

min

osity [cm

-2.s

-1]

Center-of-mass energy [GeV]

x 100

x 7

Ph. Lebrun EASITrain School 2 Saclay 2019 4


1232 twin-aperture superconducting dipolesBnom = 8.33 T, Inom = 11850 A



Superfluid helium coolingenhances performance of Nb-Ti superconductor at high field


10

102

103

104

0 5 10 15 20 25

Engi

ne

eri

ng

Cri

tica

l Cu

rre

nt

De

nsi

ty (

A/m

m²,

4

.2K

)

Magnetic Field (T)

Nb₃Sn: Internal Sn RRP®

Nb₃Sn: High Sn Bronze

Nb-Ti: LHC 1.9 K

Nb-Ti: LHC 4.2 K

Nb-Ti: Iseult/INUMAC MRI 4.22 K

High-Jc Nb3Sn

Bronze Nb3Sn

Nb-Ti

High-Jc Nb3Sn

Bronze Nb3Sn

Nb-Ti

Normal-

conducting

magnets

LHCTeVatron

RHIC HERA

FCC


Specific power consumption of particle collidersSuperconductivity and high fields

allow strong reduction of the power bill!



The beam screenA multi-function component required by thermodynamics and beam physics

• Interception of beam-induced heat loads at 5-20 K (supercritical helium)

• Shielding of the 1.9 K cryopumpingsurface from synchrotron radiation (pumping holes)

• High-conductivity copper lining for low beam impedance

• Low-reflectivity sawtooth surface at equator to reduce photoemission and electron cloud



Functions and constraints of LHC cryogenics

Functions

• Maintain all magnets at operating temperature below 1.9 K

• Handle dynamic heat loads due to magnet powering and circulation of beams

• Cooldown/warmup magnets (37’500 tons) from/to room temperature in less than 3 weeks

• Handle magnet resistive transitions without loss of helium and recoverfrom them in few hours

Constraints

• Produce refrigeration in imited numberof points (5) around machine circumference

• Re-use four 18 kW @ 4.5 K refrigerators from LEP2 project

• Distribute refrigeration in 3.3 km long sectors

• Tunnel slope 1.4 % leading to elevation differences of 150 m acrossthe ring

• Minimize power consumption


Contents







• Operation

• Upgrade


Thermophysical properties of superfluid heliumand engineering applications

• Temperature < 2.17 K superconductor performance

• Low effective viscosity permeation

– 100 times lower than water at normal boiling point

• Very high specific heat stabilization

– 105 times that of the conductor by unit mass

– 2x103 times that of conductor by unit volume

• Very high thermal conductivity heat transport

– 103 times that of OFHC copper

– Peaking at 1.9 K

– Still, insufficient for transporting heat over large distances across small temperature gradients

0,00001

0,0001

0,001

0,01

0,1

1

10

100

0 1 2 3 4 5

Temperature [K]

Spe

cific

he

at

[J/g

.K]

LHe

Cu

0

500

1000

1500

2000

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

T [K]

Y(T

) ±

5%

T

K T,q q Y T

dT

dX

q

Y(T)

q in W / cm

T in K

X in cm

2.4

3.4

2

Copper OFHC

Helium II


Pressurized vs saturated He II

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssure

[kP

a]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I


Advantages & drawbacks of He II p

• Advantages– limits the risk of air inleaks and

contamination in large and complex cryogenic systems

– for electrical devices, limits the risk of electrical breakdown at fairly low voltage due to the bad dielectric characteristics of helium vapour (Paschen curve)

• Drawbacks– one more level of heat transfer

– additional process equipment (pressurized-to-saturated helium II heat exchanger)

Paschen curve for helium


Cooling LHC magnets with He II p

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssure

[kP

a]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

LHC



Heat transfer across electrical insulationof LHC superconducting cable

Conduction in polyimide

Double wrap with partial overlap maintainsporosity and percolation paths in electricalinsulation of superconducting cable

Conduction in He II


Steady-state conduction in He II p from 1.9 to 1.8 K

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200

Length, L [m]

Qto

t [W

]

1 W/m 0.5 0.3

0.2

0.1

0.4

50

65

80

100

40

DN

Linear distributed heat load

1.8 KHe II Pres.

Cold sourceHe II Sat.(1.75 K)

Qtot= .L

SC magnet string

DNL

1.9 K (W/m)

1.8 KHe II Pres. 1.9 K

L

Cold sourceHe II Sat.(1.75 K)

Q

Superconductingdevice

DN

Lumped heat load 45 T hybrid magnet at NHMFL


Cooling magnet strings with superfluid heliumGetting the best of helium transport properties

• Fixed temperature

• Small flow, no pump

• Monophase

• Excellent thermal conductivity

• Good dielectric strength



18

LHC magnet string cooling scheme

107 m


3.3 km

Cryogenic operation of LHC sector



Contents







• Operation

• Upgrade


LHC cryostat cross-section


Thermal insulation techniquesMulti-layer reflective insulation

10 layers around cold mass at 1.9 K

30 layers around thermal shield at 50-75 K

Cold surface area in LHC ~ 9 hectares!

Thermal radiation from 290 K (black-body) ~ 400 W/m2 = 4 MW/ha

Heat flux from 290 K across 30 layers MLI ~ 1 W/m2 = 10 kW/ha



Thermal insulation techniquesLow-conduction non-metallic support posts

LHC cold mass to be supported = 37’500 tons

Conduction length = support height ~ 0.2 m

At a compressive stress of 50 N/mm2, this requires a total support cross-section of 7.5 m2, representing a large thermal conduction path

100 kN

~ 70 K

5 K cooling line (SC He)

Aluminium strips to thermal shield at 50-75 K

Aluminium intercept plates glued to G-10 column

Reflecting layer on section exposed to 300 K radiation 290 K

5 K

1.9 K

0.2 m

0.01

0.1

1

10

100

1 10 100 1000

Temperature [K]

k [

W/m

.K]

Stainless steel

Titanium

G-10



Distributed steady-state heat loads [W/m](Cryomagnets & distribution line in LHC arc)

Temperature 50-75 K 4.6-20 K 1.9 K LHe 4 K VLP

Heat inleaks* 7.7 0.23 0.21 0.11

Resistive heating 0.02 0.005 0.10 0

Beam-induced nominal** 0 1.58 0.09 0

Beam-induced ultimate** 0 4.36 0.11 0

Total nominal 7.7 1.82 0.40 0.11

Total ultimate 7.7 4.60 0.42 0.11

* no contingency

** Breakdown nominal ultimate

Synchrotron radiation 0.33 0.50

Image current 0.36 0.82

Beam-gas Scattering 0.05 0.05

Photoelectron 0.89 3.07


25

Heat inleak measurements on full sectorsconfirm thermal budget

LHC sector (3.3 km)

TPhmQ ,

Measured

He property tables

0100200300400500600700800

DR Meas. DR Meas. DR Meas. DR Meas. DR Meas.

Sector 1-2 Sector 4-5 Sector 5-6 Sector 6-7 Sector 8-1

[W]

Continuous cryostat IT 1 IT 2

On average, measured values 20 % lower thandesign estimates

Ph. Lebrun EASITrain School 2 Saclay 2019


Contents







• Operation

• Upgrade


Layout of the LHC cryogenic system

• 5 cryogenic islands

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

• Cryogenic distribution line feeding each sector


28

18 kW @ 4.5 K helium refrigerators

33 kW @ 50 K to 75 K 23 kW @ 4.6 K to 20 K 41 g/s liquefaction

High thermodynamic efficiency

COP at 4.5 K: 220-230 W/W


Challenges of high-power 1.8 K refrigeration

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssure

[kP

a]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

Pressure ratio > 80

• Compression of large mass flow-rate of He vapor across high pressure ratio

intake He at maximum density, i.e. cold

• Need contact-less, vane-less machine hydrodynamic compressor

• Compression heat rejected at low temperature thermodynamic efficiency



Warm pumping unit for LHC magnet tests3 stages of Roots + 1 stage rotary-vane pumps

6 g/s @ 10 mbar (1/160 of LHC!)


Cycles for refrigeration below 2 K

LHeCC

CC

CC

CC

CC

4.5

K r

efr

ige

rato

rHeat load

HP

MP

LP

CC

CC

CC

LHe

Sub-atmosphericcompressor

4.5

K r

efr

ige

rato

r

Heat load

HP

MP

LP

1

2

3

“Integral Cold”Compression

“Mixed”Compression

LHe

Sub-atmosphericcompressor

4.5

K r

efr

ige

rato

r

Heat load

HPLP

Ele

ctr

ica

lh

ea

ter

“Warm”Compression

Sub-cooling

heat exchanger

~ 2 kPa


32

2.4 kW @ 1.8 K refrigeration unitsCold hydrodynamic compressors

Electric drive 6’000 to 48’000 rpm, active magnetic bearings

1.8 K Refrigeration Unit Cycles

CC

He

at

Inte

rcepts

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

Ph. Lebrun EASITrain School 2 Saclay 2019


Specific features of LHC cold compressors

Axial-centrifugalImpeller (3D)

Fixed-vanediffuser

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

Activemagneticbearings

300 K

under

atm

osp

here

Cold

under

vacu

um

Inlet

Outlet

Pressure ratio2 to 3.5

Spiral volute


Performance of LHC cold compressors

0

10

20

30

40

50

60

70

80

1985 1993 2000Year of construction

Isentr

opic

eff

icie

ncy [

%]

Tore Supra

CEBAF

LHC

12

12'is

HH

HHη

Tem

per

atur

e (T

)

Entropy (s)

P1

P2

1

2

2'


Warm sub-atmospheric screw compressors

Compound two-stage screw compressor

WCS at CERN:125 g/s @ 0.6 bar

or4600 m3/h @ 15 °C

Mycom


Warm sub-atmospheric screw compressors

Kaeser

WCS at CERN:125 g/s @ 0.35 bar

or2 x 3900 m3/h @ 15 °C


Isothermal efficiencyof warm subatmospheric compressors

0

10

20

30

40

50

60

0 20 40 60 80 100Suction pressure [kPa]

Iso

the

rma

l e

ffic

ien

cy [

%]

Tore Supra

LHC Supplier #1

LHC Supplier #2

TESLA

Liquid ring pump

Screw compressors

comp

1

20

thQ

P

PlnTRn

η

Isothermalefficiency

T0 = 300 KP1

P2

Qcomp.


C.O.P. of LHC cryogenic plants


Contents







• Operation

• Upgrade


Efficiency of Joule-Thomson expansion

Sub-cooling T1’ [K] H3-H2 [J/g] H3-H0 [J/g] [%]

without 4.5 12.6 23.4 54

with 2.2 20.4 23.4 87

Sub-cooling efficiency :03

23sc

HH

HH

sc

expansion

valve

m.

Q.

LHe

Sat. He II

1.8 K, 16 mbar

expansion

valve

m.

Q.

LHe

Sat. He II

1.8 K, 16 mbar

sub-cooling

HX

1

23

1

1'

23

1'

Enthalpy of pure liquid


Subcooling before J-T expansion

1

10

100

1000

0 10 20 30 40

Enthalpy [J/g]

Pre

ssu

re [

kP

a]

Sub-cooled liquid @ 2.2 K

Saturated liquid @ 4.5 K

Saturation dome

13 % of GHe produced in expansion

46 % of GHe produced in expansion

1

22

1’

30


Subcooling HX technologies for LHC

Stainless steel sheet

Perforatedcopper plateswith SS Spacers

SS coiled tubes

Mass-flow: 4.5 g/sP VLP stream: < 1 mbarSub-cooling T: < 2.2 K

DATE

SNLS

Romabau


Protection against air inleaks

• Motor shaft of warm sub-atmospheric compressors placed at thedischarge side to work above atmospheric pressure.

• For sub-atmospheric circuits which are not under guard vacuum or notcompletely welded, apply helium guard protection on dynamic seal ofvalves, on instrumentation ports, on safety relief valves and on criticalstatic seals

I

VLP circuitsSafety valves Instrumentation and components

not completely welded,without double O-ring joints

Static sealwith double O-ring joints

HP helium

PT

Evacuationfor periodic rinsing

He guard header


Contents







• Operation

• Upgrade


Local Cryogenic

control room

Central Control Room

OWS [1..x]

PVSS DS Sector

OWS

[1..x]

PROFIBUS DP

networks

PROFIBUS PA networks

WFIP

Networks (7)

RadTol

electronics

UNICOS

PLC

S7-400

Siemens

FECs

(FESA)

RM sector 81

RM sector 78 RM sector 78

PLC

QUIC

Schneider

Return

Module

Cryo instrumentation expert tool

PVSS DS

TT, PT, LT, DI, EH CV

Controls for LHC cryogenics21300 AI, 7000 AO, 18400 DI, 4200 DO

4700 analog control loops


Cryogenics in CERN Accelerator Control Centre

On shift 24/7

Process synoptics and control

Trend curves

Fixed displays


Display of cryogenic operation indicators


Contents







• Operation

• Upgrade


LHC temperature history 2009-2019(D. Delikaris)


Cooldown to 80 K: 600 kW per sector with up to ~5 tons/h liquid nitrogen

Precooling 37’500 t magnets with 10’000 t liquid nitrogen


Helium inventory management

Total He inventory of LHC accelerator: 135 tonsOn-site storage: 125 tons« Virtual » storage contract: 60 tons

Storage capacity GHe @ 2 MPa, Tambient:- 58 x 250 m3 tanks- 40 x 80 m3 tanks

Storage capacity LHe @ 0.1 MPa, 4.5 K:- 6 x 120’000 liter vacuum-insulated vessels


Availability of LHC cryogenics 2010-2018(D. Delikaris)


LHC helium losses 2007-2019(D. Delikaris)


Contents







• Operation

• Upgrade


The HL-LHC projectObjectives and contents

• Determine a hardware configuration and a set of beam parameters that will allow the LHC to reach the following targets:

– enable a total integrated luminosity of 3000 fb-1

– enable an integrated luminosity of 250-300 fb-1 per year

– design for m 140 ( 200) (peak luminosity of 5 (7) 1034 cm-2 s-1)

– design equipment for ‘ultimate’ performance of 7.5 1034 cm-2 s-1 and 4000 fb-1


Major intervention on 1.2 km of LHC ring

• New IR-quads using Nb3Sn superconductor

• New 11 T Nb3Sn (short) dipoles

• Collimation upgrade

• Cryogenics upgrade

• Crab Cavities

• Cold powering

• Machine protection


Paths to high luminosity

Beam-beam effect precludes too low crossing angle


𝑳 = 𝒏𝒃𝑵

𝟐𝒇𝒓𝒆𝒗𝟒𝝅 𝜷∗ 𝜺𝒏

𝑹; 𝑹 = ൗ𝟏 𝟏 +𝜽𝒄 𝝈𝒛𝟐𝝈

Increase bunch population

Reduce beta at collision Reduce emittance

Increase R = reduce crossing angle?


The HL-LHC projectFrom accelerator physics to technology


Increase bunch population

Reduce beta at collision

Reduce emittance

Reduce crossing angle

Increase intensity & brightness of injectors:

the LIU project

More powerful cryogenicsImproved collimation

Improved machine protection Stronger R to E relocation

New low-beta quadrupoles

Limit beam-beam effect

“Crab” cavities

Acce

lera

tor

ph

ysic

s

Acce

lera

tor

tech

no

log

y


Additional cryogenics for HL-LHC(S. Claudet)

P7

P8

P6

P5

P4

P3

P2

P1

Existing cryoplant

New HL-LHC cryoplant

+

P1 and P5

o 2 new cryoplants (~15 kW @ 4.5 K incl. ~3 kW @ 1.8 K)

o 2 x 750m cryo-distribution for high-luminosity insertions

P4

o upgrade (+2 kW @ 4.5 K) of existing LHC cryoplant (18 kW @ 4.5 K)


Some references

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

• Ph. Lebrun, Industrial technology for unprecedented energy and luminosity: the Large Hadron Collider, EPAC9 Lucerne, JACoW (2004) 6-10

• LHC Design Report, vol.1, The LHC Main Ring, CERN-2004-003-V-1 (2004)

• Ph. Lebrun, Advanced technology from and for basic science: superconductivity and superfluid Helium at the Large Hadron Collider, Inaugural Lecture of the Academic Year 2007-2008 -Politechnika Wroclawska/Wroclaw University of Technology, CERN-AT-2007-030 (2007)

• Ph. Lebrun, Commissioning and First Operation of the Large Hadron Collider, Proc. ICEC23 Wroclaw (2011) 41-48

• Ph. Lebrun, The LHC accelerator: performance and technology challenges, in LHC physics, Scottish Graduate Series, Taylor & Francis, ISBN 978-1-1398-3770-2 (2012) 179-195

• D. Delikaris et al., The LHC cryogenic operation: availability results from the first physics run of three years, IPAC4 Shanghai, JACoW (2013) 3585-3587

• Ph. Lebrun & L. Tavian, Cooling with superfluid helium, Proc. CERN Accelerator School Erice 2013, CERN-2014-005 (2014) 453-476

• S. Claudet et al. Helium inventory management and losses for LHC cryogenics: strategy and results for Run 1, Phys. Procedia 67 (2015) 66-71

• Ph. Lebrun, Twenty-three kilometres of superfluid helium cryostats for the superconducting magnets of the Large Hadron Collider, in J. Weisend (ed.) Cryostat design, Springer, ISBN 978-3-319-31150-0 (2016) 67-94

cryogenics for the large hadron collider (lhc): design ......easitrain school 2, cea saclay 1st...

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