C ryogenics for cold-powering at LHC P7

The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.

Cryogenics for cold-powering at LHC P7

U. WagnerCERN

1st HiLumi LHC / LARP 2

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Topics• Boundary conditions• Mechanical• Lay-out• Process

• Retained cooling circuit

• Influence on the performance of the existing LHC refrigerators

• Items do be defined, designed, build and installed

• Open questions


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Boundary conditions LHC P7• Replacement of ARC current

feed boxes from LHC tunnel to adistant underground cavern.

• ~ 30 kA total current;

• ~ 500 m “semi horizontal” SC link line.

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Locations I: P7

· Cryogenic supply from existing refrigerators at P6 and P8

· Available fluids for cooling defined by existing infrastructure

· Separation of fluids!· No mixing of helium from P6 and P8 refrigerator.

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1st HiLumi LHC / LARP

ARC MS

Ref.

DFB

ARCMS

Ref.

DFB

P6 P7 P8

Existing New

Tunnel

Surface

Cold powering line

Underground cavern~ 3 km ~ 3 km

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Assumptions

· He consumption for current lead cooling:· As published by A. Ballarino in

CERN/AT 2007-5

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· The following assumptions were first formulated in 2010.· They are still the baseline today

· Link SC is MgB2

· Splice LTS to MgB2 (magnet to link) requires liquid helium bath.

· Max MgB2 temperature 20K· Max. helium temperature 17 K


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Helium conditions at interface P7 Average actual values

Sector 6-7 Sector 7-8

Line identifier

Comment T[K]

P[kPa]

T[K]

P[kPa]

Line C SC helium supply

5.3 450 5.1 390

Line D Beam screen return

22.2 125 16.5 125

Line E Thermal shield supply

70 1480 73 1450

Line F Thermal shield return

71 1720 74 1710

Worst case considered for study

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Transfer line option1: “Flexible” Nexans transfer line

· Advantage: · Easier to install; · Potentially allows to install whole length “prefabricated” with MgB2

inside.· Potentially allows to avoid splices on MgB2.· This could be a demonstrator for power lines with interest reaching

above the CERN project

· Disadvantage:· High heat load; assumed 0.3 W/m cold line; 2.5W/m shield line.

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Transfer line option2: Custom made rigid transfer line

· Advantage: · Low heat load; assumed 0.04 W/m cold line; 1.5W/m shield line.• These values have been demonstrated for the link line installed in P3.

· Allows transfer line with thermal shield supply and return lines.

· Disadvantage: · Installation in sections; time consuming; integration of MgB2 will

potentially need sections -> splices.

· As the consumption on the cryogenic system is relevant for existing installations both options are always compared.

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Conclusions from 2011 presentation

· For P7, low current case· Heat load on transfer lines defines the cooling flow.· Valid for both TL options.

· Flow in excess for current lead cooling is heated to ambient. (“wasted”)

· Invest design effort to obtain a transfer line with low heat leak.· Complex custom design transfer line· Shield circuit using 60 K, 18 bar gas (as already realised in P3)

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Cost of cooling comparison• Two reference cases• Actual cooling with DFB in the tunnel.• Lower limit.• Reference for comparison as this case does not

solve our problem.

• LTSC link, as already realised in LHC P3• Upper limit• Valid reference as possible to implement without

any further R&D.


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• The 17 K limit for the MgB2 link allows only the 5 K, 3.5 bar helium from

line C as coolant.• The link will be cooled by helium gas created by evaporating the liquid

helium in the spice box.• Thermal shield solution not shown.• Either with 20 K, or with 70 K gas.

Current Base concept (all sites)

Helium from line C

Helium at max. 17 K


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Studied cooling options• In total eight different cooling options were

studied

• The three most relevant are listed below• “Nexans like” line:• Shield cooling with 20 K gas.

• Custom line:• Shield cooling with 20 K gas.• Shield cooling70 K gas and cold return line.


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Cooling methods sketch

Shield cooling with 20 K gasNexans and Custom

Shield cooling with 70 K gasCustom only


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Comparison of cooling methods

Additional capacity

T at Lead[K]

Relative Cost[-]

4.6 - 20 K[W]

20 - 280 K[g/s]

50-75 K [W]

Actual LHC 4.5 1.00 0 0.0 0

Custom 70 K shield 6.8 2.67 125 -0.2 750

Custom 20 K shield 6.8 3.44 125 1.7 0

Nexans 20 K shield 17.0 5.87 218 3.8 0

LTS solution 4.5 10.18 579 4.1 750

Capacity margin (only if add. refrigerators) 7000 5.0 10000

Requires TL with three cold lines, discarded for MgB2 as only minor advantage.

Reference .

Kept in mind if integration of Nexans line impossible.

Values without uncertainty / overcapacity margin


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Equipment modifications•Modify DFBM• Include a link from DFBM to DFBA for the 4 x

600 A leads• (either NbTi or MgB2)

•Modify DFBA• Including the “Splice box” and the 13 kA leads

for power extraction.• Possibly, but not necessarily with a modified

jumper from the QRL


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Modified tunnel DFB

? From DFBM ?


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Additional equipment• Two link cryostats• Transfer line with shield cooling and

integrated MgB2 conductor.

• Two new cavern DFB’s• (may be in one cryostat but with separation

of the hydraulic circuits)

• Two warm lines DN80• From cavern DFB to helium ring line.


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Cavern DFB (principle flow scheme)


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Uncertainties as of last year• MgB2 performance and detailed requirements.• Progress has been made, we may consider this a minor

uncertainty.

• Lead performance and detailed requirements.• Can we assume that the lead performs close to what

was published for the LHC lead?

• Transfer line design (link cryostat)• Uncertainty remains, less for design but for realisation.


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Uncertainties and recommendations 2013• Nexans like transfer line• Desire to preassemble 500 m of “semi rigid” line with MgB2

conductor.• Handling the preassembled length?• Pulling the conductor without breaking it may be a major

challenge!

• Alternative: produce the line at the supplier with the MgB2

included; i.e. wind the line around the conductor.• This was quoted by Nexans as possible.• A demonstrator would be needed before any decision.• To be considered when in the project stage to include this

approach.


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Uncertainties and recommendations 2013• Any other than the integrated 500 m design might require MgB2 to MgB2

splices in helium gas.• At least a demonstrator that this can be feasible should be developed.

• Basically: if we can link MgB2 to HTS at 17K one should be able to

realise a link at lower temperature.

• The total pressure difference for the 20 K gas between supply and return is only about 150 mbar• The pressure loss budget at the moment is:• 50 mbar in the link line, 50 mbar in the DFB heater, 50 mbar in the return line.

• The connection between Q6 (DFBM) and the main link line.

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Conclusion 2013

· We are certain that we can supply the cooling for the current feed boxes and the corresponding superconducting link.

· We do know sufficiently well what and how we will cool.

· In short:

· We know what we want to do and we know that we can do it.· But we still need to get a clear idea about the

details.

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C ryogenics for cold-powering at LHC P7

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