the tore supra cryogenic system design and … · the tore supra cryogenic system ... the tore...

1The Tore Supra cryogenic system P. Reynaud

TORE SUPRAAssociationEURATOM-CEA

MATEFU Spring school April 2009 Cadarache

THE TORE SUPRA CRYOGENIC SYSTEM

Design and operation

P.Reynaud





Outline

• Introduction : conception of the Tokamak

• Heat dissipations and constraints

• Design of the cryogenic system

• Operation of the cryogenic system

• Cryoplant availability

• Conclusion

The Tore Supra Cryogenic system




Thick casing

Conductor (NbTi, Cu, CuNi) 1.8K

Thin casing

Polyamide alumina chocks

Glass epoxy spacers

Supercritical heliumcooling channels 4.5K

Toroïdal field coil exploded view

• Average current density : 50A/mm²,

• 4.5 T on the plasma axis,

• 9 T Peak field on the conductor.

Conception of the Tokamak

• Tight envelop performed by the thin casing • Thick casing acting as: - mechanical reinforcement,- magnetic shield,- thermal shield.




Torus cross section

Plasma

External vacuum vessel (20°C)

External 80K thermal shield

Internal 80K thermal shield

Thick casing and winding pack (4.4 K and 1.8 K)

Internal vacuum vessel and first wall (120-200°C)


All components are enclosed in a common vacuum vessel actively pumped




Torus assembly

Module of magnet/ thermal shield/ vacuum vessel

80K thermal shields





Torus assembly


Torus constituted by assembly of 6 modules of 3 coils

20t120t40 tMass

WindingsComponent ShieldsCasings




•Permanent losses

•Variable field losses

• Hysteretic losses α (DB)• Coupling losses α (dB/dt)2

windings

Insulating shocks

Wc

Normal shot (5kJ)

Plasma current disruption (15kJ)Low energythanks to efficient magnetic shielding

Low energythanks to efficient magnetic shielding

Fast discharge IT à 1250A (150kJ)

Winding pack heat loads

Heat dissipation and constraints




• variable field losses

• Permanent losses

= f (dIp/dt)2

Eddy currents

During the plasma shots (< 150kJ)

During the cleaning discharge (>= 1.MJ)

During the plasma current disruption (>= 1.2MJ)

Thickcasingwinding

Supportinglegs

Wc

Thick casing heat loads





Thermal radiation

Thermal conduction (supports)

Particular conditions :The bakingThe Baking of the vacuum vessel is one of the techniques used to obtain very low impurity release conditions Baking is effective in removing water, volatile hydrocarbons and hydrogen.Vacuum vessel temperature is led and maintained to around 200°C (473K) during several daysRadiation heat loads on thermal shields of vacuum vessel increase about 100%

Particular conditions :The bakingThe Baking of the vacuum vessel is one of the techniques used to obtain very low impurity release conditions Baking is effective in removing water, volatile hydrocarbons and hydrogen.Vacuum vessel temperature is led and maintained to around 200°C (473K) during several daysRadiation heat loads on thermal shields of vacuum vessel increase about 100%

Wr

80K shields Vacuum vessel

Plasma

Internal shield

External shield

300K

Wc

1-Permanent losses

2-variable losses (negligible)

80 K thermal shields heat loads





20 kW--Static load(baking at 200°C)

12kW300 W120 to 160 WStatic load (vessel at 120°C)

-2 s1.5 / cycle2 s0.2 / cycle

Cleaning Discharge

-8 min40035 min235Fast Safety Discharge

-25 min120012 min50Disruptions

-4 min1204 min30PF cycle

Heat loadRecovery

timeHeat load

(kJ)Recovery

time

Heat load(kJ)

Transient load

80 K4.5K1.8 K

Summary of the design heat dissipations


The instantaneous power dissipated can be 10 times larger than average loads




Contraction of SS function of temperature

1000 mm

997 mm

DL/L=3mm/m

300K 80K

negligible

80K 4.5K

DL/L=0.1 mm/m

1000mm

999.9mm


Other constraints : the cool down• Major requirements are led by the differential contractions between materials function of temperature.

• Mechanical constraints during transients cooling down or warming up must be contained to avoid any plastic deformation of structures or between thick casing supports and thermal shields

• The contraction of materials is significant between 300K and 80K, therefore, between these values, the temperature gradient between any part of the system must be kept under 40K.

• To respect the previous requirement and to optimize the duration of the cool-down , the maximum speed rate of cooling down has been fixed at 2K/h to limit the temperature gradient between the thick casing and the centre of the windings

• In practice, the cool-down of the whole system from 300k to 1.8K takes around 15 days




• The Toroidal Superconducting Magnet at 1.8K (HeII bath) with comfortable margin,

• The thick casings at 4.5K (supercritical helium),

• The thermal shields at 80K (GHe),

Design of the cryogenic system

Summary of the design requirements- Providing the cold power to :

• Diagnostics, Neutral Beam test beds, Gyrotrons, Magnet Group test beds ..

- Liquefying helium and distributing LHe for the batch users :

- Ensuring a safe cool-down of the system following requirements on temperature gradients, with a reasonable duration,

- Using thermal storages, allowing the installed cold power to be lower than instantaneous heat loads,

- Including redundancies, to preserve the cold parts from fast divergences of temperatures in case of any failure of the system

- Adopting operational modes depending on plasma operation, for energy savings purpose.




W

Helium réfrigération : « Cycle de Claude »HP

BP13

14

1

2

113

4

9

H=cst

5

6

78

T

S7 ’

6 ’

H1

H2H3

W

1

2

3

4

5

6

78

9

10

11

12

13

W

JT valve

14

E1

E2

E3

E4

E5

C

6 ’

7 ’

Isenthalpic

Cold power = m ∆H = m(H8-H7)


•The architecture of the refrigeration box is based on this thermo dynamical cycle

•The system sets to work a warm compression station, heat exchangers, turbo expanders, and expansion devices for the liquefaction.




He II refrigeration at 1.8K

Permanent losses = 120W

P installed = 300W

Available power180W


W from 7 up to 17W / coil

2 circuits:• saturated He II• pressurized He II

windings

PF

P1-P2

LHe

HeII sat

C

He II 1.25b

1.75K - 13 mbCold source

Cold pumps

Warm ring pumps

Compression cycle

Heat exchanger

14g/s

•The windings are located in a static pressurized superfluid helium bath

•The refrigerating power is obtained by the means of evaporation by pumping




• No risk of air leakage• Easy helium transfer• Improvement of the coil stability• Increase of the critical current margin• High limiting flux, independent of immersion depth• All open and even recessed cavities are completely filled with liquid• Vapour can only appear with a high ∆T


He II pressurized for coils

P (MPa)

T (K)Tλ=2.172 K

T= 4.2 KP= 0.1MPa

0.1

Helium phase diagram

T=1.8K

He II

He I





The pumping on the He II bathes

The pumping on saturated bathes is performed in 2 parts:A cold part compresses in 2 stages 14g/s of helium gas from 12mbar at 4.3K up to 80mbar near 15K. At this pressure the helium is warmed to room temperature by standard heat exchangers.At room temperature the final compression from 70mbar could be performed by an oil ring pump.

The cold centrifugal compressors developed by L’AIR LIQUIDE run on magnetic bearings and are driven by variable speed drives developed by the S2M company.At the moment of the design of the cryogenic system, the use of this technology for this particular purpose for the first time in the world was a major breakthrough for the helium refrigeration and opened the way of larger refrigeration plants at 1.8K.

The choice of oil ring pump for the warm part of compression was also the result of comparatives studies both on technical aspects and economic costs.




The 4.5 K thick casing refrigerationDedicated power to cold source : P= 600W


P

18 thick casings

W W

LHe

pump18 MPa4.5 K

17 bar4.5K

P,TThermal ballast

3000 LHe

P

C

PRefrigerator

Super critical He Circulation at Te = 4.5 K Refrigeration

box

Principle• Casings connected in series

• Supplied with SHe coming from cold box

• Fixed inlet temperature of casings

• Thermal ballasts filled with LHe

• Operation at V=cst

• Absorption and smoothing of the loads

• Refrigeration box with evaporation

• Compensation of liquid from external tank

Practically constant operation

Lhe restocking in off-peak hours

Optimization of the cold box size




Heat loads extracted from thick casings

HeII saturated bathes pressure

Thermal behavior during plasma operation


8,5

9

9,5

10

10,5

11

11,5

07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22

Long plasma pulse 1 GJ

Plasma disruption and conditioning discharges

time (h)

Pressure (mbar)Toroidal field ramp up

200

400

600

800

1000

1200

1400

8 9 10 11 12 13 14 15 16 17 18 19 20 21

Plasma disruption and conditioning discharges

Long plasma pulse 1 GJ

time (h)

W

Toroidal field ramp up




Cool down of the toroidal magnet

T out = 227K

from SC6 at 300K

80K

from SC2 at 300K

T out = (300+300+80)/3

1st Triple exchanger


A first division by 3 is performed at therefrigerator exit in order to divide the power between the «3 satellites

300K




from SC6 at 300K

227Kfrom SC2 at 300K

T sortie = (300+300+227)/3

T sortie = 276K

2nd triple exchanger



Within each satellite, a further division by 3 is operated

300K




300K from casing at 300K

276K

T sortie = (276+300)/2

T sortie = 288K

Double exchanger

CasingN°X300K 288K

∆T BEp=300-288=12K

(300-80)/18= 12

∆ T global refrigerator / 18



Finally, divisions by 2 are accomplished




with T1+LN2 evaporation during baking

P = 30kW Increasing mass flow rate

P = 10kW

with T1 during normal operation

Available cold power from 2 sources

80 K thermal shields cooling loop

water

windings

Thermal shields

sat4sat6

First heatexchanger

CB

T1 turbine

Oil removal system

LN2

4.6 b18.6 b

18b

P

V1GHe circulation at

T = 80K

2 cold sourcesLN2 T1

80Ksat4sat6

sat2






Functional layout

Warm machine roomGathering warm compressors and pumpsIncluding Oil removal system

Providing the high pressure levels

Collecting low pressure levels

Cold boxProviding the 80K and the 4.5K levels

Liquefying helium Performing the cold pumping

Liquid helium storage

Cryogenic satellitesConnecting the different circuits

Performing the 1.8K source

Smoothing the heat loadsPart of the ∆T division

ColdBox

WarmMachines room

Torus Hall

Torus Hall




Compressor House• He screw compressors

• Oil removal systems

• He/H2O exchangers• Oil/H2O exchangers

• Oil ring pumps

• He Balloons• HP storage

• 200 bar compressors

• Coalescers

• Driers• Analysers

• He buffer tank

• Safety systems• Control &

instrumentation systems

Cryogenic Area• Cold box

• He/He Exchangers

• Gas bearing turbines• Expander engines

• Cold compressors

• 80 K GHe purifier• Charcoal adsorbers

• Analysers

• LN2 tanks

• LHe tank• Cryolines

• Vacuum systems

• Safety systems• Control &

instrumentation systems

Utilities• Vacuum system

• Water cooling systems

• Compressed air supply• Power supply

Overview of the components and utilities





Rescue cold box• Including a single heat exchanger with a LN2 evaporator

• Included set of valves,

• Linked to the thermal shields by distinct circuits

Utilities• Vacuum system

• Water cooling systems : switchable on raw water circuits

• Compressed air supply from different sources

• Power supply from different sources

• Rescue Programmable Logic Controller

Redundancies


Mainly aim to maintain the whole system under 80K,

A single cycle compressor is sufficient : 100g/s




• Within the Torus hall

- 3 colds boxes acting as cryogenic relays called cryogenic satellites,

- Each satellites contain a 1.8K source and a 4.5K thermal ballast,

- Each of satellites feeds 6 toroidal field coils,

- Each satellite is connected to the refrigerator by cryogenic lines

• Within the cryogenic hall

- The cold box

- A primary cryogenic line connected to the main cold box

• Adjoining the cryogenic hall

- 1 storage of 20m3 for LHe

- 2 storages of 50m3 each for LN2

• Within the warm machine hall( 70m from the cryogenic hall)

- The compressors and the warm pumps included in the system

- The recovery compressors

- Temporary helium storages: 200m3 and 400m3 gas bags

• Adjoining the warm machine hall

A high pressure storage (18MPa) of gaseous helium : total volume 70m3


System layout




Cases and windings

Refrigerator cold box

20 000l Lhe tank

2*50 000l LN2 tankCompressorsand pumps station

200b Ghestorage

balloon GHe

Satellites

Cryogenic lines


General overview




• First machine using a large quantity of superfluid helium

1m3 of saturated superfluid He, 4m3 of pressurized superfluid He

Cold Power at 3 levels of temperature

10 to 30 kW at 80 K

1000 W at 4.0K

300 W at 1.75K

• Electric consumed power in nominal operation : 1.2MW

• Mass at low temperature

20 000 kg at 80K shields

120 000 kg at 4.5 K thick casings

45 000 kg at 1.75 K conductors

• Cooling down duration 15 days to cool the magnet from 300 K to 1.75 K

• Fully automatic system with several operating modes for energy savings during short plasma shut down,

• 500 measurement loops, 300 cryogenic valves, 250 safety valves, 600 manual valves,

• 8 vacuum pumping systems,

• 7 Programmable Logic Controllers

The main figures





Operation of the cryogenic system

Typical Plasma experimental campaign (2006)

Plasma Operation rhythm : ~ 40 hours a week4 days a week : TF magnet at 1.8K3 days at 4.2K week-end and maintenance day (Monday)Annual Shutdown : ~ 3 months a yearHeavy maintenances: Warm Compression Station for example,Regulatory controls for pressure equipments, power supplies ,etc…Tore Supra configuration changes, etc….

weeks

Temperature of the TF magnet

1

10

100

1000

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52

week (year 2006)

Tem

per

atu

re (K

)

WINTER SHUTDOWN

WINTERSHUTDOWN

COMMISSIONING SUMMER CENTRE CLOSURE

IN-VESSEL WATER LEAK

EXPLOITATION PERIOD EXPLOITATION PERIOD

standbyat 4 K

standbyat 300 K

Heavy maintenance of the cryogenic

systems (4 weeks available per year)

Annual test of the auxiliary cold box

operationat 1.8 K




Operation of the cryogenic system

The cryoplant operational modes

Nominal operation

Liquefactionat 4 K

Warm stop

Liquefactiononly

Liquefactionat 80 K

Idle at 80 K

Liquefactionat 2 K

The more usual operational modes of the cryoplant




Time spent in the different operating modes trough years

100 %8760 h100 %8760 h100 %8760 h100 %8784 hTOTAL

28 %2440 h16 %1394 h17 %1518 h23 %2013 hTotal time spent in

transitions

28 %2445 h28 %2495 h23 %2036 h20%1770 hNominal operation

confirmed

0 %0 h0 %0 h0 %0 h2 %177 hLiquefaction at 2 K confirmed

17 %1512 h43%3645 h22 %1893 h21 %1841 hLiquefaction at 4 K confirmed

5 %399 h1 %89 h6 %558 h6 %501 hLiquefaction at 80 K confirmed

2%192 h2 %192 h7 %577 h3 %222 hLiquefaction at 300K

confirmed

5 %421 h4 %338 h10 %853 h5 %476 hIdle at 80 K confirmed

15%1342 h6 %543 h15 %1311 h20 %1732 hWarm stop confirmed

totalshourstotalshoursTotalshourstotalshoursOperating mode

2007200620052004

Cryoplant availability




28 %2445 h28 %2495 h23 %2036 h20%1770 hNominal operationconfirmed

totalhourstotalhourstotalhourstotalhoursOperating mode

2007200620052004

80 %76 %54 %53 %

Availability of the whole Tore

Supra installation

97.3 %100 %92.9 %76.2 %Availability of the cryogenic

system**

Relative availability to the plasma experimental campaign


** Relatively to experimental campaign




Tore Supra Cryoplant events

• Cold components: expanders, cold compressors, valves, exchangers.

• Instrumentation: Probe and signal conditioning.

• Process control: Hardware and software, process application

• Utilities: Water cooling, compressed air, power supplies, vacuum.

• Operation: He analysis and purification, the other faults.

• Warm components: compressors, pumps, valves, driers, ….

0%

5%

10%

15%

20%

25%

30%

Cold component

Instrumentation

Process controlUtiliti

es

Operation

Warm component


Distribution of faults during the cryoplant operation over the last 3 years 2004-2007




Cryogenics• Clogging of 80K stage exchanger of the cold box : addition of an external purifier

• Tightness breaking of Al/SS junction of thick casing circuit inside a cryoline,

• Many gaseous helium leaks : installation of a recorded helium leak detector,

• Water in oil circuits of the warm compressors in 2005,

• Pollution of the coils circuits during the cool-down in 2008,

Utilities• Very short life span of the compressor motors bearings at the beginning,

• Inappropriate system of command-control replaced by industrial PLC later

• Corrosion on water cooled black steel exchangers in the warm machine room,

• Corrosion and water leaks on vacuum diffusion pumps circuits,

• 2 total electric shutdown in the 4 last years : rescue by Electrical Mobile Groups

Main troubles encountered through years





The conception of the Tore Supra cryogenic system at the end of the 70’s was

the result of studies lead by CEA about design and sizing of 1.8K refrigeration

circuits.

More than 20 years after its commissioning, and without any large updating, the

cryogenic system is operated in quasi-industrial conditions with a satisfying level

of performance and availability.

Keeping a human presence on the site, performing daily inspections of the

critical components and a reliable and ergonomic control-command system make

possible an increase of availability during the 4 last years.

Total operating time at low temperature

140 000 h including 57 000 h at T = 1.8K

Conclusion




Flow rate

14g/s

Compression ratio 2.3

Suction conditions

34mb/10K

Cold compressor PF2

AL/S2M

Flow rate

10g/s

In/out Pressure

18/1.2bar

In/out Temperature 6/4.5K

Wet reciprocating engine

AL/KPS model 1400

Flow rate50g/s

Power2.2kW

In/out Temperature 19/10K

Turbine T3AL C4-500

Flow rate

24g/s

Power

2.8kW


Turbine T2

AL C3-500

20000l of LHe + 2 x 50000l of LN2Liquid storages

Flow rate

14g/s

Compression ratio 3Suction conditions

10mb/4.5K

Cold compressor PF1

AL/S2M

Flow rate110g/s

Power16kW


Turbine T1AL C5-500

Extra-slide

Technical specifications of cold components




Whole capacity : 1500kgPressure max

200bars

HP storage

160m3 + 360m3Gas bags

Electrical power of motor 132kW

Flow rate

60g/s

In/out Pressure

0.6/1bar

Oil ring pump P2

Alstom Hydro PL 50

Electrical power of motor

90kW

Flow rate

10g/s

Pressure max

200 bar

Recovery compressor C7

Sulzer type C5U


75kW

Flow rate

10g/s

Pressure max

200bar

Recovery compressor C8

Sulzer type C5U


400kW

Flow rate

218g/s

In/out Pressure

4.5/18bar

Compressor C4

STAL S57


250kW

Flow rate

144g/s

In/out Pressure

4.5/18bar

Compressor C3

STAL S51


200kW

Flow rate

101g/s

In/out Pressure

1/4.5bar

Compressor C2

STAL S73

Electrical power of motor 315kW

Flow rate

14 g/s

In/out Pressure 70/600mbar

Oil ring pump P1

Alstom Hydro PL 160


200kW

Flow rate

101g/s

In/out Pressure

1/4.5bar

Compressor C1

STAL S7

Extra-slide

Technical specifications of warm components

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