ILC : Type IV Cryomodule Design Meeting Main cryogenic issues, L' Tavian, ATACR Cryostat issues, V'P

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ILC Type IV Cryomodule Design MeetingMain
cryogenic issues, L. Tavian, AT-ACR Cryostat
issues, V.Parma, AT-CRI

• CERN, 16-17 January 2006

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Content

• Design pressure of cavity cold mass structure
• Minimum diameter requirement of distribution
  lines
• Cool-down and warm-up principle

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Design pressure of cavity cold-mass structure
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Design pressure of cavity cold-mass structure

• The spacing of safety device needed to protect
  the cavities depends strongly on the design
  pressure of the cold-mass structure
• High design pressure ( 3.5-4 bar)
• Discharge of helium during technical incident
  (break of beam vacuum with air) can be done via
  the pumping line (DN300) with safety relief
  valves located close to access shaft.
• Low design pressure (lt 3.5-4 bar)
• Safety relief valves must be periodically
  installed in the tunnel on the pumping line, i.e.
  ODH issues in the tunnel or large additional
  header to collect the valve discharge.

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Design pressure of cavity cold-mass structure
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Minimum diameter of distribution lines
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Cool-down and warm-up principle

• Tesla TDR principle

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Cool-down and warm-up principle

• ILC principle proposal

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Cool-down and warm-up principle
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Main cryostat design issues

• Real-estate gradient inter-cavity and cryomodule
  interconnection space optimization 1
• Cryomodule length? 2
• Thermal performance. review of static heat loads
  table 1 of bcdmain_linacilc_bcd_cryogenic_chapte
  r_v3.doc 3
• Design of thermal shielding feed-throughs and
  thermalisations (couplers, tuners, etc.) strong
  impact on cryostat thermal performance. 4
• Cryomodule interconnection design
  Length optimization, thermal design,
  interconnection bellows stability.  5 
• Cryo-string extremity modules (Technical Service
  module in LHC jargon) housing cryo equipment 2
  out of 15 cryomodules in a cryo-string. 6
• Cryogenics flow (and vacuum pumps) induced
  vibrations. Performance limiting?
  bcdmain_linacilc_bcd_cryogenic_chapter_v3.doc
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• Materials and assembly technologies
• Ti helium vessel and weldability to Ni. 8
• Ti-to-st.steel transitions leak-tightness at cryo
  T (13 units per cryomodule!). 9
• External support system (ground support vs.
  hanging) and re-alignment strategy ? impact on
  tunnel integration

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Inter-cavity space optimisation
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Cryo-module length

• Impact of cryo-module length
• Increasing length
• lt No.of interconnections ? lt No.componets
  (bellows) and installation cost saving
• So gt real estate gradient ? tunnel length cost
  saving
• lt No. critical components (bellows) ? higher
  reliability
• ? All desirable effects
• Practical limits
• Weight increase. (TTF8 tons?). Longer
  Cryo-modules will remain light objects (below
  15 tons).
• Road transport from 11 m to 15 m cryomodule
  still transportable (according to European
  regulations). LHC cryo-dipoles are 15 m long.
• Handling no major limitation, butwider tunnel
  shafts? cost increase
• ? Increase length to about 15 m or longer?

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Interconnectionsoften forgotten
LHC interconnection

• Optimise compactness ? gt real estate gradient
• Specific design of compensation systems
• Mechanical stability of pressurised lines
• (Al extruded thermal shields for LHC)
• Low stiffness/compact optimised bellows
• (plastic domain for LHC bellows)
• Do not forget thermal performance
• Appropriate (active) thermal shielding with MLI
• Beware of thermal contraction gaps in thermal
• shields (radiation multi-reflection paths).
• Cryo-module extremities need specific features

Experience gained in the past! ?
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Thermalisations
Welded Al thermal shields (50-65 K)

• Avoid bolted braid assemblies and st.steel
  brazing whenever possible
• All-welded or shrink-fitted solutions preferable
• Proper interface must be foreseen on components
  for effective thermalsations

A few LHC solutions
Al welded shrink-fit thermalisation of pumping
tubes (SSS) (50-65 K)
Thermalisation weld of support post / bottom tray
(50-65 K)
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Estimated heat loads
Table 1. Estimated values of distributed heat
loads in steady operation W/m(without
contingency)
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Vibrations
Table 4. Maximum vibration level (integrated RMS
of vertical displacement)