The%20LHC%20from%20construction%20to%20commissioning

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The LHC from construction to commissioning

• Lucio Rossi
• CERN Accelerator Technology Dept

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Particle Physics is one of the two frontiers of
the physics spectrum
Why accelerators? To investigate Particle Physics
Accelerators
Microscopes
Binoculars
Optical, radio télescopes
Particle physics looks at matter in its smallest
dimensions and accelerators are very fine
microscope or, better, atto-scope! ? h/p
_at_LHC T 1 TeV ? ? ? 10-18 m
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back to Big Bang

• Trip back toward the Big Bang t?s?1/E2Gev
• T ? 1 ps for single particle creation
• T ? 1 ?s for collective phenomena QGS
  (Quark-Gluon Soup)

• But we are left with the task of explaining how
  the rich complexity that developed in the ensuing
  13.7 billion years came about
• Which is a much more complex task!

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Why do we need technology at the edge?
2 routes to new knowledge about the fundamental
structure of the matter
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CERNs particle accelerator chain
From LINAC to LHC
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2004 The 20 member states
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The push for energy giant size
1500 tonnes of top quality SC cables
1800 Power Converter from 60 A to 24 kA
Bdip? 8.3 T Rdip ? 3 kmLdip ? 15 m ?
1232Ltunnel 27 km
15000 MJ of magnetic energy
1800 HTS Leads 11 kW_at_1.9 K
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The LHCFor 20 years it has been a viewgraph
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Rationale for superconductivity in accelerators

• Circular Accelerators
• Ebeam 0.3 B r GeV T m
• ? superconducting bending and focussing
  magnets
• high-energy hadron synchrotrons
• Linear Accelerators
• Ebeam E L MeV MV/m m
• ? superconducting acceleration cavities
• high-energy linacs

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Rationale for superconductivity in accelerators

• Electromagnets (d.c.)
• Resistive
• Power per unit length P/L rCu j B
• Total power (Joule) P rCu j B r rCu
  j Ebeam
• Superconducting
• Total power (refrigeration) P r
• for given operating
• temperature, power
• consumption is only
• cryogenic, i.e. independent
• of field

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Rationale for superconductivity in accelerators

• The LHC has a circumference of 26.7 km, out of
  which some 20 km of main superconducting magnets
  operating at 8.3 T. Cryogenics will consume about
  40 MW electrical power from the grid.
• If the LHC were not superconducting
• If it used resistive magnets operating at 1.8 T
  (limited by iron saturation), the circumference
  would have to be about 100 km, and the electrical
  consumption 900 MW (a good-size nuclear
  power plant), leading to prohibitive capital
  and operation costs.

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Cost structure of the LHC
Total cost 4 G
Magnetcryogenics 66
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The power of the LHC beams
The LHC beam energy is 350 MJ. Already at
injection the beam can damage a magnet.
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LHC tunnel 2002
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LHC tunnel 2006
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Regular arc Magnets
1232 main dipoles 3700
multipole corrector magnets
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Regular arc Magnets
392 main quadrupoles 2500 corrector magnets
Installed dipole
SSS being transported
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Connection via service module and jumper
Supply and recovery of helium with 26 km long
cryogenic distribution line
Static bath of superfluid helium at 1.9 K in
cooling loops of 110 m length
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Insulation vacuum for the cryogenic distribution
line
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quench protection, power converters for orbit
correctors and instrumentation (beam, vacuum
cryogenics)
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Inner triplet magnets
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Accelerator magnets issues

• In iron dominated magnets the pole shape dictates
  field quality
• In superconducting magnets the conductor position
  dictates the accuracy of the field.
• Coils not self-supporting
• Beam will circulate 500 Millions times in the
  LHC ! Field accuracy 10-100 ppm
• Necessity to have all dipoles equal in length
  within 100 ppm (1.5 mm over 15 m of the LHC
  dipole length !)

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The hystorical outlook
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The LHC superconductor 7000 km of Cu/Nb-Ti cable
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Critical Current of LHC inner cable
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Magnetization for LHC NbTi
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Rutherford cables
Needs for 10-20 kA cable for protection Needs
very high packing factor 90 !! Needs a system
simple that keep strands
resistive contact Rc at cross-over point
The strand are fully transposed BUT field changes
over a period ! Ends problems Junctions BICC
? dB/dt
induced eddy currents in the loop I ? -dB/dt and
I ? 1/Rc
superconducting path in the strands
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Controlling the contact resistance
CERN has developed the controlled oxidation
method Value too low gives field errors Too
high may give instability
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Number of tests in 2003 at CERN
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QA Laboratory Equipment( 300 K tests)
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QA Laboratory Equipment
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Cable for main dipoles delivery
International permanent review
Multiple suppliers helped however only a few
were really critical for the project
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Coils - Winding

• Accurate positioning?for quench?for field
  accuracy
• Winding
• Curing at 185 C
• 3-D ends. Quasi-impregnation

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Critical ProcessWinding-Curing-Coil
30 µm
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Dipole cross section Collars
Collars and collaring are the main controllers of
the final coil shape Fine blanking of special
austenitic strips (?rlt1.005).

• Collaring press
• gt 20 MN/m
• 700 mm wide
• 450 mm high
• Beam accuracy 20 ?m

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QA Magnetic measurements
Introduced first to steer the FQ toward beam
dynamics targets.
Team of 3 physicists dedicated to on-time
analysis covering also holidays periods. 4 hours
to react yes-no-hold 2 days max time to
accept/reject hold-on cases
It has also helped to detect a number of
defects. It has also been used to detect subtle
electrical shorts
Courtesy of E. Todesco and C. Vollinger
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Steering the production through Field Quality
AT-MAS
To get it right we need model predicting position
and deformation at 10-20 micron
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Dipole cross section yoke shrinking cylinder
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Dipole -end partend plate
Also MQ
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Dipole-end part Bus Bars
Also MQ
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Dipole -end partShrinking cyilinder
Also MQ
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Dipole -end partCu HXT
Also MQ
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Dipole -end partCorrector Magnets
Also MQ
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Dipole -end partCold foot, Bellows and N-line
Also MQ
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Snapshot at IndustrySuperconducting poles
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Snapshot at IndustryAperture assembly
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Snapshot at Industrycollaring process
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Snapshot at IndustryCold Mass
Laser Tracking measurements
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Snapshot at IndustryCold Mass waiting
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Snapshot at Industrydelivery to CERN
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Snapshot at Industry MAIN Quadrupole
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6000 of various corrector magnets
MCDO Decapole Octupole Magnets
MCS Sextupole Magnets
MO Octupole Magnets
MQSXA Quadrupole Octupole Sextupole Magnets
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Superconducting LHC dipoles the long route
1988-98 short models and six prototypes for each
of the three generation design were built by
industry/CERN
1999 3x30 pre-series magnets were ordered from
three firms.
Three contracts for the fabrication of 1146 (30
spares) magnets have been signed March 2002
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Integrated supply chain management
CERN took care of most components

• Benefits
• Technical homogeneity
• Quality assurance
• Economy of scale
• Security of supply
• Balanced industrial return

• Risks drawbacks
• Responsibility interface
• Additional workload
• Liability for delays (just in time!)
• Transport, storage logistics we have moved
  120,000 tonnes around Europe (5 TIRs a day for 5
  years)

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LHC components industrial products
Industrial production
Art!
Courtesy of Ph. Lebrun
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Series production of LHC components
Courtesy of Ph. Lebrun
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90 main supply contracts worldwide
Europe in details
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Personnel training in Coil production
Courtesy of Jeumont, France
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LHC Learning Curvecollared coil production
Courtesy of Babcock Noell, Germany
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Log Linear model learning
curves FIrm 3
Fit Crawford model
Collared Coil production 800-1000h Cold Mass
Production 500-1000h
Work done with P. Fessia
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Comparison with other industries
Industry r
Complex machine tools for new models 75-85
Repetitive electrical operations 75-85
Shipbuilding 80-85
LHC magnets 80-85
RHIC 85
Aerospace 85
Purchased Parts 85-88
Repetitive welding operations 90
Repetitive electronics manufacturing 90-95
Repetitive machining or punch-press operations 90-95
Raw materials 93-96
LHC Main Dipoles
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Learning phases? Different drivers?
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Number of toolingnumber of firm

• The number of tooling has been correct (the goal
  was 3-4/week per company
• Less companies (for example 2 instead of three)
  would not have lessened significantly the unit
  price and would have led to high risk

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Dipole performance today
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The great success the dipole delivery
review
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A milestone achieved
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Magnet work flow at CERNbefore beam test
Cold test
Arrival CM
Cryostat
Reception
Cryostat
Cold test
Reception
Arrival CM
Beam screen
Extra-work (30 dip)
Store 4 areas
Stripping Fiducials
Beam screen
Store 4 areas
Extra-work (30 dip)
Stripping Fiducials
Alignment
Tunnel
Store limited number
Connections
Connections
Alignment
Tunnel
Store limited number
1st dipole lowered 7th March 2005
Hardware Commissioning
Beam test
Beam test
Hardware Commissioning
December 2007
Start January 2007
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Experienced important setbacks QRL

• In Dec 2001 the contract to single supplier
  awarded to Air Liquide
• Installation started 21 July 2003
• Suspended after a few months conflicts between
  AL and subcontractors
• Re-started in spring 2004 and then suspended in
  May for leaks, when a good part of 7-8 was
  already installed. The delays were already
  consistent
• Endoscopic examination in June 2004 revealed
  broken support. Work were stopped

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QRL
Sliding table
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Welding defects inspection of 18 service
modules in August 2004
Temper colour 100 Scaled surface 100
End crater pipe 100 Root concavity 30
Root porosity 50 Incomplete root penetration 45
Inspections of other elements at CERN and at
factory will continue
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QRL handled

• The company, near to drop the contract, has
  re-committed itself to the project.
• CERN took over the dismounting, repair and
  re-installation for all 7-8
• CERN has supported follow in subcontracting and
  coped (also financially) in a high rate plan to
  catch up the delays.
• AL and CERN has reviewed all design (tables,
  weldings, alignment, bellow instability, etc.)
• The first octant completed 1.8 months delay
• The last only less than 1 year in delay
• However the consequence are still there (for
  example the ICs team was widely diverted to QRL
  repair and then IC did not start with the wanted
  quality. The rate requested for installation and
  IC has been double than foreseen

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Another item that has caused delay DFB
Production in Protvino now finished
CERN re-insourced activty will end in May 2007
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Main work today IC

• Late start, accelerated rate
• 200 people in the tunnel
• 100 contractor
• 100 CERNassociated for managing, QA, repair,
  in-sourcing of special WPs

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IC - 2

• New technologies introduced
• u.s. welding for single wire
• Induction heating for large cablegood but
  problems in passing to high rate
• Some IC of 7-8 must be reopened since we have
  doubts
• The 200 people in double shift are barely seen in
  the 27 km tunnel!

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IC status

• Today we are working, as IC in 7 octants !!!
• In Sept 06 work done was 15. At half April the
  work done has passed 2/3 !!
• Arc (DS) finished by end of August 2007
• Long straight section by end of September 2007
  (triplet last repair is not integrated)

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The plague electrical NC Q4R8 quench heater
circuit problem

• Abnormal quench heater voltage decay trace and
  abnormal resistance of the heater after its first
  powering in the tunnel
• Quench heater is short to ground
• Magnet will be used as is thanks to the quench
  heater redundancy
• Quench heater power supply and interlocks had to
  be modified

Arcing across open circuit
Good circuit traces
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A short to ground of the main dipole circuit at
warm It has been repaired with acrobatic
intervention

• A short to ground of the main dipole circuit
  during the high voltage qualification

• The fault has been localized inside a dipole
  magnet on the compensation loop of the dipole
  bus-bar
• Confirmation by endoscope after opening the
  interconnection
• The fault has been repaired in situ

Electrical Quality Assurance of LHC circuits, D.
Bozzini, V. Chareyre CERN/AT/MEL
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Interim short circuits to ground on the main
defocusing quadrupole circuit

• Detection of interim short circuits to ground on
  the main defocusing quadrupole circuit during the
  first phase of the cool-down (300 K to 80 K)

Electrical Quality Assurance of LHC circuits, D.
Bozzini, V. Chareyre CERN/AT/MEL

• The location of the fault was estimated with
  accuracy of /- 10 meters
• The short has disappeared after the restart of
  the cool-down

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Q9R3 A short to ground of the quadrupole circuit
at warm

• Detection of the short circuits to ground on the
  quadrupole circuit during the warm electrical
  quality assurance tests
• Drawings analysis has revealed that the busbars
  in SSS 500 series are to long by 40mm
• Corrective action (shortening of the busbar
  extremities) is underway on the 32 SSS-500

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Resistance of the DFLS.5L8 circuit

• An abnormal resistance has been measured on one
  corrector circuit of a stand-alone magnet that
  supposed to be superconducting

Electrical Quality Assurance of LHC circuits, D.
Bozzini, V. Chareyre CERN/AT/MEL

• Powering of the circuit is blocked
• Further diagnostics and analysis is underway

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HV breakdown of 4 corrector circuits at cold

• 4 corrector circuits had a discharge during
  voltage ramping-up to 600 V. The breakdowns have
  been identified among the circuits.

Routing through the cold-mass. Tested at cold on
magnet test bench
Instrumentation Feed-through System tested at 3.1
kV
Standard connector for instrumentation tested at
1kV
Current leads tested at warm in gaseous He at 1kV
Electrical Quality Assurance of LHC circuits, D.
Bozzini, V. Chareyre CERN/AT/MEL
Lead to bus-bar connection
Suspected area
Bus-bar interconnection
Bus-bar interconnection

• Powering of the 4 concerned circuits is blocked
• Further diagnostics and analysis is underway

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HWC

• ElQA after pressure test
• Cool down
• ElQA at 80 K
• ElQA at 4.2 K on some circuit and DFB
• Full ElQA at 1.9 K
• Power test
• 4 Octants full
• 4 Octant reduced at 2 KA (11.85 kA nominal)
• Also HWC has been strongly compressed (long term
  QRL effects). Strong participation of associated

Courtesy of Roberto Saban
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HWC - global view
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j
?
j
?
?

• All magnets isolated and active cooling in
  thermal shields and cryogenic lines
• ?Turbine filter exchange with thermal shield
  cooling stop

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j Tuning of cold compressors turbines with
temporary stop of magnet cooling
k Stop of active cooling in weekend with only on
call activity limited to secure hardware l Stop
of magnet cooling for logic improvement in 1.8K
refrigeration unit m Random emergency stop in
cryogenic surface building with stop of sector 78
cooling ? Micro-electrical stop followed by
utility stops
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1.9 K cooldown along the arc
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Follow-up of Helium inventory
Based on 29 l/m
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Major events towards 1.9K

• Utilities
• Power (400V failure on 30Mar07, with cascade
  effect on cooling water 2h45, control networks
  45, mobile vacuum pumping units. Situation
  restored 10h45 without re-cooling the
  cryo-magnets
• Cryogenic part
• Progressive set-up of procedures to pump-down to
  15mbar, while keeping DFBs with 4.5K conditions
• Continued upgrades in instrumentation (Level
  gauges, Heaters, ) but more efforts required to
  improve reliability and availability
• About to start testing the magnet temperature
  control loops for 1.9K operation
• 1.8K Refrigeration unit trip (frequency drive)
• Difficulties to restore 1.9 K conditions after a
  stop
• First tests of  CRYO Start  and  CRYO
  Maintain  signals, to be continued as  verbal 
  powering authorisation could have soon some
  limits!
• Clients
• DFBAs Cryo cmg underway with cooling of current
  leads under tuning
• ELQA_at_1.9K Underway, as in fact 3-4K is enough!

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Cool-down milestones

• OK for HW Cmg on DFBMs Stand-alone magnets
• Early troubleshooting on other DFBs continued
• Entire arc 7-8 below 2.0K on April 5th, 2007
• Difficulties to restore 1.9 K conditions after a
  stop
• Efforts to be continued (instrumentation, logic,
  procedures) while preparing for powering

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CPP - cryogenic actions

• Current activities
• 1.8 K units pumping down to 15 mbar
• Supercritical helium distribution temperature
• Heat loads and inventory assessment
• Valve sizing assessment
• CRYO_START and CRYO_MAINTAIN validation
• DFBMA commissioning
• Level sensors in-situ calibration
• Temperatures mapping on chimneys with different
  control parameters
• Added heating power on chimneys to avoid
  condensation
• Analysis of phase separator and stand-alone level
  gauges measurements
• Analysis of possible line Y interruption around
  Q9

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1.8 K units pumping down to 15 mbar - actions on
the 1.9 K

• Cold compressors trip during pump down
• Cause
• Cells phase separator with liquid helium
  perturbing the pumping flow during lambda
  transition (up to 60 pumping flow increase)
• Consequences
• Delays in the recovery of nominal conditions
  after stops
• Action plan
• Reduce the quantity of liquid in the return
  module phase separators
• Interlock to close the supply valve after a trip
  (debugging)
• Avoid connecting cold compressors at saturation
  pressure (eq. saturation temperature) higher than
  the colder cold mass temperature

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The real problem Supercritical helium
distribution temperatures
We should be working here
and were there!
Courtesy of PhL
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Supercritical helium distribution temperatures

• Supercritical helium temperature above
  specification
• Cause
• EX-LEP refrigerator subcooler not adapted for LHC
  operation as seen last autumn
• Consequences
• Difficulties for some transients adaptation
• DFBs feed limitations
• Action plan
• Preparation for new cryoplant connection
  (process logic and interlocks)
• Sector 7-8 fed by new cryoplant
• Consolidation of ex-LEP subcooler being
  investigated for implementation before autumn
  2007 after sector 7-8 warm-up

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Heat loads preliminary assessment on sub-sectors
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Valve sizing assessment JT valve

• Valve opening
• Measured around 1 3
• Expected 13 23
• Possible causes
• Lower stand-by heat loads gt valve outside design
  range
• Valve sizing incorrect gt manufacturer error
• -gt request modification of flow plug
• Consequences
• Difficult control of magnets temperature
• Increased risk of oscillations and perturbations
  on the whole system
• Action plan
• Test bench measurements on a spare valve
• Discussion with valve manufacturer
• Assessment of heat loads to confirm flow rate
• Valve characterization with additional electrical
  heating in the cold masses
• Valve consolidation (plug exchange) for sector
  4-5 before cooldown
• Valve consolidation (plug exchange) for sector
  7-8 after warm-up

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DFBMA commissioning

• Level sensors readings and condensation on top
  flanges
• Different level sensors show different readings
• 120 A assemblies cannot be cool down to nominal
  operating conditions (20 K) due to condensation
  (below 5 deg C)
• Minimum temperature achieved 26 and 36 K (4 and 8
  leads assemblies)
• Possible causes
• Supercritical helium temperature
• Position of level sensor near helium feed
• Convection paths in the chimneys
• Pt sensor precision at 20 K
• Warmer helium intake from adjacent chimneys for
  larger cooling flows
• Consequences
• Delay in nominal cryogenic conditions for magnet
  powering
• Action plan
• Improve supercritical helium distribution
  temperature
• Calibrate the level sensors against geometrical
  changes in the vessel / leads
• Increase level to observe possible cooling flow
  reduction
• Verification of Pt sensors calibration curve
• Additional heating on chimneys top flange

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Where we are today

• Struggling for cryogenics
• The program of HWC is delayed of about 1 month
• At least two octants to warm up (for many
  reasons)
• But closing the rings will be done on schedule
  (triplet impact to be assessed)
• Have we lost the engineering run in 2007 ?
• We dont care we keep this goal.