L. Serio 1.6.2007

COPING WITH TRANSIENTSCOPING WITH TRANSIENTS

L. SERIOCERN, Geneva (Switzerland)

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

LHC Parameters (p-p) LHC Parameters (p-p) impacting on Cryogenicsimpacting 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 130x103 kg

L. Serio 1.6.2007

0

14000

-3000 -2000 -1000 0 1000 2000 3000

Time [s]

MB

cu

rren

t

0

1

2

3

4

5

6

7

8

9

B [

T]

RAMP DOWNSTART RAMP

PHYSICS

PREPAREPHYSICS

BEAM DUMP or QUENCH

PREINJECTIONPLATEAU

INJECTION

T0 Tinj

SQUEEZE

PHYSICS

Ramp down 18 Mins

Pre-I njection Plateau 15 Mins

I njection 15 Mins

Ramp 28 MinsSqueeze 5 Mins

Prepare Physics 10 MinsPhysics 10 - 20 Hrs

LHC operation cyclesLHC operation cycles

L. Serio 1.6.2007

Cryogenic system main Cryogenic system main functionsfunctions

Cope with load variations and large dynamic range induced by the operation of the accelerator

Cool down and fill but also empty and warm-up the huge cold mass of the LHC in a maximum time of 15 days

Cope with the resistive transitions of the superconducting magnets minimising loss of cryogen and system perturbations

Limit the resistive transition propagation to the neighbouring magnets and recover in few hours

Cope with the resistive transition of a full sector

Allow for rapid cool-down and warm-up of limited lengths of cryo-magnet strings, e.g. for repairing or exchanging a defective diode

L. Serio 1.6.2007

Overview of the cryogenic systemOverview of the cryogenic system

5 cryogenic islands

8 x 4.5 K refrigerators • (144 kW @ 4.5 K, 600 kW

precooler and heater)

8 x 1.8 K refrigeration units• (19 kW @ 1.8 K)

25 km of superconducting magnets in superfluid helium

– several 1’000’s control loops:– 1400 for current leads– 320 for magnets temperature– 600 for beam screen– several 1’000’s for refrigerators(distribution line)

(interconnection box)

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

Cooling towers

Compressed air

Vacuum10-3 mbar

Cooling and ventilation4800 m3/h of water

Helium and nitrogen130 t of He – 4.3 MCHF

10’000 t of LN2 – 1.6 MCHF

Electric powerabout 32 MW; 24 GWh/month

1.2 MCHF/month

LHC COOLDOWNLHC COOLDOWN

CRYOGENICSControls:Networks, fieldbuses, PLC, SCADAMass to be cooled [t] 36’800

Max He flow [g/s] 6160

Max cooling capacity 300-160 K [kW] 4800

Liquefaction rate [g/s] 1000

L. Serio 1.6.2007

Arc cooling principlesArc cooling principles

L. Serio 1.6.2007

0

50

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350

15-Jan 30-Jan 14-Feb 1-Mar

Time (UTC)

Tem

per

atu

re [

K]

4.5 K refrigerator supply temperature Return temperature

Thermal shields temp. (average over sector) Magnet temperature (average over sector)

Thermal shield

temp.

Supply

temperature

Return

temperature

Magnet

temperature

cooldown 300 - 80 K

cooldown 80 - 20 K

cooldown 20 - 4.5 K

LHC COOLDOWN 300 to 4.5 KLHC COOLDOWN 300 to 4.5 KTime Evolution of Cold Mass Temperatures

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0 1 2 3 4 5 6 7 8 9 10 11 12

Time [d]

Tem

pera

ture

[K]

Q1in D1in D2in D3in Q2in D4in D5in D6in D6out

L. Serio 1.6.2007

Final cooldown to 1.9 KFinal cooldown to 1.9 K

L. Serio 1.6.2007

LHC COOLDOWN 4.5 to 1.9 KLHC COOLDOWN 4.5 to 1.9 K

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40

Time [hour]

Col

d-m

ass

tem

pera

ture

[K

]Normal operation

Fast operation

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

Cell Cooling Principle (I)Cell Cooling Principle (I)

Slope

MagnetSaturated LHeII

Magnet cell (107 m)

Bayonet heat exchanger

GHe pumping (15 to 19 mbar)

SHe supply (4.6 K, 3 bar)

Ps0

Wetted length (Lw) Dried length (Ld)

JT

Hydraulicplug

PressurisedLHeII

TT TT TT TT TT TT TT TT

L. Serio 1.6.2007

Cell Cooling Principle (II)Cell Cooling Principle (II) Pressurised LHeII:

• Content: 26 l/m• Free cross-section: 60 cm2

Bayonet heat exchanger:• Linear thermal conductance: 120 W/m.K• Free inner diameter: 54 mm

Control principle:• The JT valve controls the temperature difference between:

- the maximum of cell temperature TT and- the saturated temperature Ts0 corresponding to Ps0.

• As a consequence:- the bayonet heat exchanger is partially dried,

- the wetted length increase with the heat deposition.

L. Serio 1.6.2007

Temperature Excursion Temperature Excursion during Injection Sequenceduring Injection Sequence

0

10

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-0.5 0 0.5 1 1.5 2 2.5 3Time [hour]

T [

mK

], I [

kA

]

0

0.4

0.8

1.2

1.6

2

Pu

mp

ing c

ap

aci

ty [

kW

]

Magnet current Pumping capacity

T cell #1 T cell #27 The magnet current ramp-up and de-ramp from 0 to 12 kA with a rate of 10 A/s (Eddy currents dissipate 480 J/m in the cold masses)

Heat partially bufferedby helium content

Maximum temperatureexcursion: 50 mK

L. Serio 1.6.2007

Typical LHC ramp to nominal Typical LHC ramp to nominal

current (11860 A)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 11:40

0

2

4

6

8

10

12[kA], W/m[K]

0.2 W/m 0.3 W/m - 0.6 nOhm

Temperaturestability : 5 mK

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

Beam induced loadsBeam induced loads

L. Serio 1.6.2007

Beam Squeezing TransientBeam Squeezing Transient

Beam squeezing• Fast transient heat deposition (few minutes)• Heat loads (secondaries due to inelastic collisions):

- 1.7 W/m in Nominal conditions- Up to 4 W/m in Ultimate conditions- Proportional to the beam luminosity

Ratio up to 20 with respect to the static heat inleaks

Control principle• Feed-forward control for ratio above 3• “Normal” control for ratio below 3

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

Temperature Excursion during Temperature Excursion during Fast Current Ramp-downFast Current Ramp-down

-50

0

50

100

150

200

250

300

-0.5

0 0.5 1 1.5 2 2.5 3

Time [hours]

T [

mK

]

0

2

4

6

8

10

12

14

Curr

en

t [k

A],

Capaci

ty [

kW

]Magnet current Pumping capacity

T cell #1 T cell #27 Magnet current fast ramp-down from 12 to 0 kA with a rate of 80 A/s, for which Eddy currents dissipate 3000 J/m in the cold masses.

Magnet temperatureremains below T(helium stays in superfluid state)

Recovery time: 2 hours

L. Serio 1.6.2007

500 kJ.m-1 stored magnetic energy dissipated in the windings (see M. Chorowski spot)

Pressure rise contained by discharge every 106.9 m by cold safety valves (see R. Couturier spot)

Discharged helium buffered into header D or discharged and recovered from header D into gas storage vessels

Quench and helium Quench and helium recoveryrecovery

L. Serio 1.6.2007

Recovery Time after Limited Recovery Time after Limited Resistive TransitionsResistive Transitions

A resistive transition warms up the magnets to 30 K More than 14 cells or full sector recovery up to 48 hours

L. Serio 1.6.2007

ContentsContents Introduction

• Systems, principles and parameters

Cooldown• Principles and key figures• From simulations to sector cooldown

From steady state to nominal powering• Principles and key figures• From simulations to full scale experiments

Working with circulating beams• Principles and key figures• From simulations to full scale experiments

Fast current discharges and quench• Principles and key figures• From simulations to full scale experiments

Conclusion

L. Serio 1.6.2007

ConclusionsConclusions

The cooling principle of the LHC magnets and the cryogenic plants will:

• In steady-state operation, maintain the arc magnet temperature below 1.9 K with temperature stability within 10 mK

• In-between the different steady-state operation modes, give a temperature stability within 70 mK

• Not limit the cycle rate of injection• After a fast current ramp-down, maintain the magnet temperature below T, but a

recovery time of 2 hours is required• Because of local random losses, give a maximum temperature excursion of 20 mK• After a limited resistive transition, give a beam down time of 4 to 7 hours

Individual system, full scale prototype and final full sector tests have validated the basic design and operating principles as well as demonstrated a high level of availability achievable after the necessary commissioning time required by this complex but performing system