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C ryogenics for cold-powering at LHC P7. U. Wagner CERN. Topics. B oundary conditions Mechanical Lay-out P rocess Retained cooling circuit Influence on the performance of the existing LHC refrigerators Items do be defined, designed, build and installed Open questions. - PowerPoint PPT Presentation
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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
1st HiLumi LHC / LARP 3
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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.
4
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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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
7
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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1st HiLumi LHC / LARP 10
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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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