LHC Systems

1
LHC Systems

• Cryogenics.as seen by Beam Handlers
• G. Arduini, S. Redaelli
• Many thanks to
• A. Butterworth, S. Fartoukh, M. Giovannozzi, A.
  Rijllart, L. Serio, F. Zimmermann

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Outline

• LHC Cryogenic system overview
• Instrumentation and Signals
• Cryo-Organization during Beam Commissioning
• Application SW
• Cryogenics powering
• Cryogenics commissioning with beam
• What could go wrong during beam commissioning?
• Tools needed
• Summary

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LHC cryogenic system layout
L. Serio
4
LHC Cryogenic System layout

• No redundancy for sector 2-3 in case of problems
  with the cryogenic unit in point 2 and no fast
  cool-down possible
• Naming
• Q Cryogenic System
• S, U Surface, Undergorund
• C, R, I Warm compressor, Refrigerator,
  Interconnection Box

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LHC Cryogenic Components in Tunnel
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Instrumentation and signals

• Available instrumentation and signals in the
  tunnel
• Pressure gauges (PT)
• Temperature gauges (TT)
• Level gauges (LT)
• Valve opening (CV)
• Virtual flow meters at the valves (based on
  pressure drop and temperature measurements,
  tables on He characteristics, valve opening,
  etc..) (FT)

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Instrumentation and signals
L. Serio
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Instrumentation and signals
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Cryo-Organization during Beam Commissioning

• On-line
• Planned 1 8 h shift on-call operators and
  experts
• Possible 2 8 h shift on-call experts (as for
  HW commissioning)
• Ideal 3 8 h shift on-call experts
• In the case of process faults (e.g. spurious
  faults, partial HW faults) the presence of a
  cryo-operator could limit the recovery time and
  even avoid beam-dumps and could be essential in
  case of teething problems
• Off-line
• Cryogenic Performance Panel (CPP Chair L.
  Serio)
• Analyze off-line, manage all aspects of cryogenic
  performance,
• Study, propose improvements of functional
  procedure and consolidations,
• Record and track cryogenic sub-system performance
  in relation to their manufacturing and test data.
• Design and set-up of the tools for the additional
  on-line monitoring of the cryogenics during beam
  commissioning
• ? provide crucial feedback for the steering of
  the beam commissioning

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Application SW

• High level of detail in the application available
  in CCC.
• Possible to navigate through the Cryogenic
  system.

• Four access levels (the first three with
  password)
• Administrator omnipotent
• Expert login for experts only, direct control on
  each piece of equipment of the cryo system.
  Possibility to change interlock level.
• Operator can operate the system, accessing the
  equipment but cannot change interlock levels.
• Monitor Read access only ? this is the mode in
  which we should use the application
• Under deployment nominative access with
  role-based rights

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Sector 7-8 Navigation bar
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Sector 7-8 (arc)

• GreenOK
• YellowWarning
• RedNot Ok
• BlueInvalid Data
• PurpleNot Avail.

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Sector 7-8 Navigation bar
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Sector 7-8 Inner Triplet L8 DFBX
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Temperature overview for each sector
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Signal overviews for the Sectors
Cold Mass temperatures
Pressures
He levels
Line C temperatures
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Sector 7-8 (arc)
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Trends

• Predefined sets or operator defined
• Possibility to select the trend of one parameter
  from overview or synoptic plot

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Cryogenics Post-Mortem - General information

• PM analysis based on check functions defined by
  experts
• LabView Logic specified by the Cryogenics
  Performance Panel in Excel tables, interpreted by
  a LabView program, this is part of the Magnet PM
  analysis software provided by CO/MA.
• Four PM event triggers CRYO_START,
  CRYO_MAINTAIN, QUENCH, ALARM. They can be
  triggered on request ? PM can be used also as
  analysis tool!
• For the moment, only expert logic is implemented
• The tools seem flexible it should be possible to
  add a beam-oriented logic for the PM analysis.
• PM application retrieves data from the logging
  data-base
• Delay of a few minutes before data are available
  for analysis
• Inconsistency between the logging and measurement
  DB have been observed
• Filtering and smoothing of the data before
  transfer to the logging DB can false the trends
• ? why not accessing the measurement data-base?

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Cryogenics Post-Mortem application - snapshots
Buttons that simulated 4 PM events (CRYO_START,CRY
O_MAINTAIN,QUENCH,ALARM)
Display of selected signals
Main table with results of PM analysis (analysis
type and results given)
Signals for the plot
Faulty signals (did not pass the test)
Signals with no data (last acquisition reported)
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Some additional features
Sorting results (signal name, analysis
type) Possibility to save and retrieve the
results of the analysis are available and
required in particular if access to the
measurement DB is implemented
Signals to graph
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Cryogenics conditions for powering

• There will be three logic states for each
  powering sub-sector
• Conditions to authorize magnet powering
  (CRYO_STARTTRUE and CRYO_MAINTAINTRUE)
• Conditions that do not authorize magnet powering
  but if there is already current in the magnets
  there is no request for discharge (the conditions
  of magnet powering were met at the time of the
  start of powering but have disappeared meanwhile)
  (CRYO_STARTFALSE and CRYO_MAINTAINTRUE)
• Conditions that do not authorise magnet powering
  and request a slow current discharge
  (CRYO_STARTFALSE and CRYO_MAINTAINFALSE)
• 32 Powering sub-sectors
• 3 types per sector
• ITD1 (in IR2 and 8)DFBX (8 in total)
• Matching Section standalone magnets _at_ 4.5
  KDFBM,DFBL,DSL (12 in total)
• ARC DFBA (8 in total)
• 4 RF modules

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CRYO_START / MAINTAIN

• No direct connection of Cryo with BIC but only
  with PIC
• Only insulation vacuum is directly interlocked to
  cryogenics (lt10-3 mbar, expect a steady state of
  10-6 mbar if no leaks).
• No direct connection (no interlocking) between
  Beam Vacuum and Cryogenics Bad beam vacuum ?
  Higher heat load ? CRYO_START and CRYO_MAINTAIN
  might disappear

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Cryogenics commissioning with beam

• Assumptions
• The Cryogenics system should be fully
  commissioned during the HW commissioning period ?
  in that case its behaviour as a function of the
  powering levels (energy dependence) should be
  understood
• The main remaining unknown is the interplay of
  the beam with the cryogenics system
• Heat load on the beam screen due to
• resistive dissipation of image currents
• synchrotron radiation
• electron cloud
• Heat load on the cold masses due to
• Nuclear inelastic beam-gas scattering (depending
  on the vacuum level)
• Other type of beam losses (e.g. beam halo losses
  and energy deposition from the induced showers)

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Cryogenics commissioning with beam
per aperture
600
900
1300
2200
L. Tavian LTC 2/6/2004 F. Zimmermann LTC
6/4/2005
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Cryogenics commissioning with beam
LHC Design report L. Tavian LTC 2/6/2004

• A priori no need for dedicated time for
  cryogenics studies with beam but parasitic
  follow-up of the behaviour of the cryogenics in
  the presence of beam as a function of its
  parameters ? monitoring by Cryogenics Performance
  Panel. Its feedback will be crucial in steering
  the commissioning (in particular the increase in
  intensity)

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Critical elements

• Are there elements which are more critical than
  others?
• Magnets
• Q6 in IR1 and 5 (standalone magnet at 4.5 K) as
  evidenced by quench behaviour
• MQTLs
• In general SC magnets close to collimation areas
  and triplets in the interaction points
• Q4 close to the beam dump area
• Interaction with and feedback from MPP is vital
  to define critical elements
• RF
• Coupling with the rest of the sector might be an
  issue
• Little margin for the pressure levels ? Beam dump
  at 1.5 bar
• Cryo limit could be reached if we try to run with
  less cavities but higher field
• Sector 2-3 no redundancy
• Sector 3-4 and 4-5 are the most critical
• From the point of view of the heat load (due to
  the additional load from the RF in IR4)
• 4-5 is also critical from the point of view of
  the temperature due to the hydrostatic heads
  because of the slope on the LHC ring

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What could go wrong during beam commissioning?
L. Serio AB/OP shut-down courses 7/3/2007
Cryo commissioning presently ongoing is the first
chance to test all the systems together and their
interactions. More might have to be learned when
we will start to inject beam.
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What could go wrong during beam commissioning?

• Quenches will be the routine
• More than 14 cells or full sector ? recovery up
  to 48 hours
• In case of fast discharge (even w/o quench) ? 2 h
  recovery (heating due to eddy currents).

L. Serio Training Day for the Commissioning of
the LHC Powering System 29/3/2007
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What could go wrong during beam commissioning?

• Strong correlation cryogenics vacuum
• Vacuum transients might result from
• excessive condensation of gases on the beam
  screen in the cells adjacent to a quenched one ?
  warming-up of the Beam Screen (to 40 K) might be
  required (few hours required) before injecting
• Operation of the beam screen at temperatures
  close to 24 K (instead of 20 K) e.g. as a result
  of localized losses can result in emission of CO
  from the Beam Screen and reduced lifetime

V. Baglin Chamonix XIII
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What could go wrong during beam commissioning?

• Heat loads above specifications
• In that case heat load measurements and
  comparison with expectations are essential before
  any increase in intensity
• The resolution in heat load on the beam screen is
  0.5 W/cell to be compared with 280 W/cell as
  expected beam induced heat load at nominal
  intensity at 7 TeV. The expected margin in
  nominal conditions is 40 W/cell. Possible mean
  to see pressure bumps?
• Local heating on cold masses can be measured with
  the resolution of a cell and localization within
  a cell might be possible by measurements of the
  temperature difference between magnets
• EM-interference induced by the beam on the
  sensors
• Past experience (SPS) has shown that sensors
  (e.g. temperature sensors) can be affected by the
  beam presence in particular for high intensity
• Main difference sensors are not in direct view
  of the beam
• Countermeasures redundancy and filtering
• This should manifest itself as a
  non-deterministic behaviour of some of the
  control loops.
• Could be a nightmare

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Tools needed

• Certainly we will need a summary of the Cryo
  Maintain/Start conditions for the different
  Sub-Sectors
• Available soon

L. Serio
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Tools needed

• If the Cryogenics parameters start to drift on
  time scales of minutes probably there is not much
  that we (or the Cryogenics Expert) can do to
  re-establish stable conditions and save the
  beam
• Follow-up of the trends when the mode of
  operation is changed (intensity or energy
  variation) is vital for planning the
  commissioning steps and minimizing down-time
• We could specify analysis types relevant for LHC
  operation in the PM and trigger it via alarms (on
  trends) or external triggers.
• Define virtual heat loads on beam screens and
  cold masses from temperature, flow, pressure
  measurements and heater setting (started by CPP)
• Monitor heat load and temperatures on beam screen
  and cold mass, correlate with vacuum, beam
  intensity, beam losses and compare with
  expectations
• Add temperature/flow trends to identify
  critical behaviour based on signal evolution
• Later fixed-displays could take overonce the
  measurements and measurement devices are fully
  mastered and the needs and problems clarified

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Summary

• The behaviour of the cryogenics as a function of
  the powering levels (energy dependence) should be
  understood before beam commissioning ? a priori
  no dedicated time required during beam
  commissioning but the beam presence might
  introduce additional unexpected effects.
• The presence of cryo-operators on 3 x 8 h shift
  during beam commissioning could help to sort-out
  potential teething problems of the cryo-system
  and to reduce beam down-time during the
  commissioning.
• Interaction with CPP and MPP should be
  strengthened in order to focus on the critical
  elements and refine the analysis tools for beam
  commissioning.
• Detailed SW tools exist to assist the expert in
  the control of the cryogenic system
• For beam operation heat loads are probably the
  most meaningful parameters understanding of
  their trends could be very useful to identify and
  anticipate problems. The resolution (also
  spatial) should be sufficient.
• Non-expert tools need to be enhanced ? The
  post-mortem analysis fishing in the measurement
  DB could be a powerful tool for the Beam
  Commissioning period although later fixed
  displays could be developed.

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References

• LHC Design Report Chapter 11 - Cryogenics
• LHC-Q-ES-0004 (EDMS 710799) The circuit of the
  LHC cryogenic system
• LHC-Q-ES-0003 (EDMS 710797) Functional analysis
  of the LHC cryogenic system process
• L. Serio, Cryogenics and powering - Training Day
  for the Commissioning of the LHC Powering System
  29/3/2007
• L. Serio, LHC Cryogenics AB/OP shut-down
  Courses 7/3/2007
• L. Tavian, LTC 02/06/2004
• F. Zimmermann, LTC 06/04/2005
• V. Baglin, Vacuum Transients during LHC
  Operation, Chamonix XIII