OPERATIONAL EXPERIENCE ON CRYOGENIC SYSTEMS FOR …1st Workshop on Cryogenics Operations Jefferson...

1st Workshop on Cryogenics Operations Jefferson Laboratory - Newport News US - March, 30 2004

OPERATIONAL EXPERIENCE ON CRYOGENIC SYSTEMS FOR

LARGE-SCALE ACCELERATORS AT CERN

S. CLAUDET, M. SANMARTI, L. SERIO, L. TAVIAN

Cryo Ops 2004 - JLab - Newport News US - March, 30 2004 L. Serio, CERN2

Contents

• Introduction• LEP cryogenics

– Overview– Operational experience

• LHC cryogenics– Overview– Operational experience

• LHC cryogenics future operation


Cryogenic Refrigeration Capacity at CERN

0

20

40

60

80

100

120

140

160

180

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

kW @

4.5

K

OMEGA, BEBCISR Low-Beta

ALEPH, DELPHI,LEP Low-Beta

LEP2

LHCATLAS, CMS

LEP2+

The largest helium liquefaction center in the world!Courtesy of Ph. Lebrun


C.O.P. of Large Cryogenic Helium Refrigerators

0

100

200

300

400

500

TORESUPRA

RHIC TRISTAN CEBAF HERA LEP LHC

C.O

.P. [

W/W

@ 4

.5K

]

Carnot

Courtesy of Ph. Lebrun


Transport of Refrigeration in Large DistributedCryogenic systems

0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5Distance [km]

Tem

pera

ture

diff

eren

ce [K

] Pressurised He II Saturated LHe II He I

Tore Supra

TevatronHERA

UNKLHC

SSC (main Ring)

SSC (HEB)

LEP2 TESLA



Thermodynamic States of He in CERN accelerators

1

10

100

1000

10000

1 10 100 1000T [K]

P [k

Pa]

SOLID

HeII

HeI

CRITICAL PT

GAS

Thermal Shields

Beam Screens

HTS Partof Current Leads

Resistive Part of Current Leads

SpecialMagnetsArc

Magnets

HeatExchanger

Tubes

RFCavities

LEPLHC



He Inventory of Large Cryogenic Systems

0

50

100

150

200

250

300

Tevatron HERA CEBAF RHIC LEP2 LHC (SSC)

[tonn

es]

VirtualLiquidGas @ 2 MPa

60%

28%

7%5%

Cold massesHeader COther headersCryoplants

Total LHC inventory:96 tonnes of He

LOSSES %inventory/yrUtility stops 30Operation 15Purge/conditioning 5TOT losses 50


Introduction

Cryogenics for LEP2 accelerator

72 Modules installed and 4 SCQ

Point 2 Point 8

Point 4 Point 6

20

2016 + 2 SCQ

16 + 2 SCQ

•LEP operation since 1989

•Installation of SC cavity modules and cryoplants from 1992

•Four 12/18 kW @ 4.5 K:

Storage tanks, compressor station, upper cold box (300-20 K)

Lower cold box and distribution lines (200-250 m)

Cryo Ops 2004 - JLab - Newport News US - March, 30 2004 L. Serio, CERN

LEP2 Cryogenic system progress

0

5000

10000

15000

20000

25000

30000

1992 1993 1994 1995 1996 1997 1998 1999 2000

Runn

ing

hour

s [h]

IP8IP6IP4IP2IP2-6kW

Upg

rade

12

kW to

18

kW

Operation & Maintenance Contract

Results Oriented


Cryogenics vs. LEP2 Project ( Po wer ba lance)

02468

101214161820

1996 1997 1998 1999 2000

Equi

v. c

oolin

g po

wer

[kW

]

2030405060708090100110

Nb

of m

odul

es &

bea

m e

nerg

y [G

eV]

shielding Static load Dynamic load liquefaction loadNb Modules LEP Energy Total heat load Available Power

Cry

o U

pgra

de•Dynamic losses

(RF field)^2/Qf

•Thermal Shield

2 kW/cryoplant•Static losses

27 W/module

80W/TL & val.

•Liquefaction

0.8g/s x module


Exploitation Team

Staff Evolution

0

5

10

15

20

25

30

35

1995 1996 1997 1998 1999 2000

Pers

on-y

ear

APT Staff CERN Staff Total

APT Staff (LEP2)

1 Eng. & 4 Oper.6 person-year Maint.1 person-year Manag.

CERN Staff Contract monitoringTechnical assistanceInterfaces with LEP


Operation Performance & statistics

More than 120.000 h accumulated. Cryo avg. failure downtime:

Cryogenic system downtime rates from 1996 to 2000

0.00.51.01.52.02.53.03.54.04.5

1996 1997 1998 1999 2000

Dow

ntim

e ra

te [%

]

Cryo failures rateUtility failures rateDe-icingLEP impact

Cryo

Upg

rade

7 per 1000 h. ofLEP operation(0.7 %)

Utility failuresdowntime:1.5 %

De-icing: reduced cooling capacity. Time used for machine develop.


Cryogenic Issues for LEP Machine• High reliability of LEP2 cryogenic system

– Preventive maintenance and fast repair during operation– Up-to-date documentation and well-trained operators

• Influence of the circulating beam– Bunch length sensitivity and proportional to beam current^2– High losses in RF antenna cables (cooling modified)

• Thermoacustical Oscillations: outlet transfer line

• Turbine filter clogging: reduction of cooling capacity available and risk of filter destruction (after upgrade)

– 1st and 2nd turbine filters at 120 and 90 K respectively– H2O and CO2 traces respectively (spectroscopy)

• Periodic de-icing (warm up and cleaning)– Duration (6-10 hours) & scheduling in collaboration with LEP

• Design weakness– Buckled bellow in vertical transfer line, plate-fin heat exchanger– Upgraded turbines and oil separation system

• Major technical problems after maintenance shutdowns (after restart)– Twice for motor bearings, once for a compressor (out of 24)– Fixing structures of compressors skids to the floor

• Aging of components (starting from 30’000 hours)– Compressors oil injection piping, oil pumps, air and He leaks


LHC Parameters (p-p) impacting on Cryogenics• Circumference 26.7 km• Beam energy in collision 7 TeV• Beam energy at injection 0.45 TeV• Dipole field at 7 TeV 8.33 T• Luminosity 1034 cm-2.s-1

• Beam intensity 0.56 A• Energy loss per turn 6.7 keV• Critical energy of radiated photons 44.1 eV• Synchrotron power per beam 3.8 kW• Stored energy per beam 350 MJ• Operating temperature 1.9 K• Cold mass 36.8x106 kg• Helium inventory 96x103 kg


Duties of the LHC Cryogenic System

• Basic– Maintain all magnets below 1.9 K in normal operation– Cool-down and fill (respectively empty and warm-up)

a machine sector in less than 2 weeks– Accommodate resistive transitions of full cells and

recover from them in few hours• Additional

– Allow rapid cool-down and warm-up of limited-length strings for repair or exchange of magnet

– Accommodate generalized resistive transition of a sector without helium loss


Constraints of the LHC Cryogenic System

• Existing LEP tunnel– 3.8 m diameter (in arcs)– 3.3 km-long sectors– deep underground with limited access shafts and

technical service areas– 1.4 % slope and elevation differences– suburban and rural region

• Reuse of LEP cryogenic infrastructure– 4 helium refrigerators of 12 kW @ 4.5 K, upgraded

to 18 kW– piping and storage vessels


Overview of the cryogenic system 1/2

• 5 cryogenic islands• 8 refrigerators

– 2 at P4, 6 and 8, – 1 at P2 – 1 at P1.8

• 1 refrigerator serves 1 sector (18 kW @ 4.5 K, 600 kW precooler)

• possibility to couple two refrigerators via the interconnection box 2 refrigerators for 1 sector

(distribution line)(interconnection box)


Overview of the cryogenic system 2/2

UpperCold Box

Interconnection Box

Cold Box

WarmCompressor

Station

LowerCold Box

Distribution Line Distribution Line

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

ColdCompressor

box

Shaf

tS

urfa

ceC

aver

nTu

nnel

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

MP Storage

WarmCompressor

Station

WarmCompressor

Station

WarmCompressor

Station

ColdCompressor

box

MP Storage MP Storage

Even pointOdd point Odd point


Warm Compressor Station of 18 kW @ 4.5 K Cryoplant(Power Input ~4 MW)


LHC 18 kW @ 4.5 K Cold Box33 kW @ 50 K to 75 K 23 kW @ 4.6 K to 20 K 41 g/s liquefaction

• 1st in operation since 2002

• 2002– 6600 hours– Availability:

Reduced capacity 99 %Full capacity ~80 %

– 220 hours “on-call” intervention

• 2003– 5700 hours– Availability: 99.4 % – 190 h “on-call”

intervention (3.3 %)Major consolidations• motor-compressors skids• oil injection valves• shaft seal lubrication• Turbine bearing and brake

regulation• He-N2 precooler HX


LHC 18 kW @ 4.5 K Cold Box33 kW @ 50 K to 75 K 23 kW @ 4.6 K to 20 K 41 g/s liquefaction

• 1st in operation since end 2003

• 600 hours

Major consolidations

• motor-compressors skids

• oil injection valves• shaft seal

lubrication• Verification of N2

precooler HX capacity


Specification 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

efrig

erat

ion

Uni

t

LHe 1.8 K Q1.8K

CC

B

4.5 KRefrigerator

B

D

C

Col

d co

mpr

esso

rs

Turb

lne

Adsor-bers

LHC SectorLoad


Cold Compressor Boxes of 1.8 K Refrigeration Units

Air LiquideCold Compressor box

IHI-LindeCold Compressor box


1.8 K refrigerators measured performances

0

20

40

60

80

100

120

140

0 15 30 45 60 75 90 105 120

Time (min)

11

12

13

14

15

16

17

18

Inlet

Pres

sure

(m

bar)

Mass Flow

Tolerance

Set-Point

AL - Inlet Pressure

IHI-Li Inlet Pressure

Magnet ramp-up

Physics

Beam abort

Air Liquide : ±0.3 mbar !

IHI - Linde :± 2.2 mbar ...


LHC Cryogenic Components in Tunnel


LHC Magnet Test String

• String 1 1995-1999– 13000 hours @ 1.9 K – 172 quench – 15 thermal cycles– 3275 electrical cycles

• String 2 2001-2003– 8300 hours @ 1.9 K– Availability: 97.3 %– 3 thermal cycle– 42 quenches – 130 h “on-call”

intervention (1.6 %)


Typical LHC ramp to nominal current (11860 A)

1.7

1.75

1.8

1.85

1.9

1.95

2

10:50 11:00 11:10 11:20 11:30 11:400

2

4

6

8

10

12[kA], W/m[K]

0.2 W/m 0.3 W/m - 0.6 nOhm

Validation of performance and sizing rules of the bayonet heat exchanger

for transporting linear heat loads in the W/m range

Verification of budgeted heat loads (20.4 W) within the precision of

measurement (+/- 1.9 W)


4 Control Rooms:(2) accelerators

(1) techn. services(1) cryogenics

What is controlled:• Accelerators• Transfer lines• Exp areas• Access systems• Electricity• Cooling• Vacuum• Cryogenics


Integrate the all operation functions into ONE CERN Control Centre: the CCC. Manned with 12 operators on 3x8 shift.

3 operators dedicated to Cryogenics2 operators “on-call”Maintenance activities outsourced to external firm(s)


Legend:QRLQUIRefrigeratorArcDispersion SuppressorsLong Staight Section

LHC commissioning/operation planning

P1

P3

P6P4

P8P2

P1.8

P7

P5

Be n d i n g a r c

S e c t o r ~ 3 . 3 k m

Operation

CommissioningP1

P3

P6P4

P8P2

P1.8

P7

P5

Be n d i n g a r c

S e c t o r ~ 3 . 3 k m

Operation

CommissioningP1

P3

P6P4

P8P2

P1.8

P7

P5

Be n d i n g a r c

S e c t o r ~ 3 . 3 k m

Operation

CommissioningP1

P3

P6P4

P8P2

P1.8

P7

P5

Be n d i n g a r c

S e c t o r ~ 3 . 3 k m

Operation

Commissioning

2004200520062007Injection test


Conclusions• LEP2 cryogenic system has shown high reliability and

remarkable operation performance with– carefully planned maintenance and periodic checks– up-to-date documentation and well-trained operators

• Operation/maintenance can be successfully outsourced but requires:– commissioning and first years operation by the staff that designed it

• It could be a long adaptation process– minimum staff dedicated to upgrades, consolidations, monitoring and

interface with other accelerator systems

• The LHC cryogenic system basic design criteria, main choices and functionalities have been successfully tested

• Plants and equipments are being installed, commissioned and are progressively going into operation


Conclusions

SUMMER 2007

OPERATIONAL EXPERIENCE ON CRYOGENIC SYSTEMS FOR …1st Workshop on Cryogenics Operations Jefferson...

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