A Preliminary Look at the ILC Cryogenic System

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A Preliminary Look at the ILC Cryogenic System

• Tom Peterson, Fermilab
• ILC RD Meeting
• 8 February 2006

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ILC 500 layout
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ILC modules and cryogenic system are closely
based on the TESLA Technical Design Report (TDR)

• TESLA TDR is available online (see references)
• 9-cell niobium RF cavities at 1.3 GHz and 2
  Kelvin are the primary accelerating structures
• Cavities are assembled into a cryostat called a
  cryomodule or module
• ILC module concept is still the TDR module,
  except 8 cavities instead of 12 per module
• TDR cryogenic system concept is retained

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ILC cryogenic system effort is a very active
collaboration

• CEA Grenoble, CERN, DESY, Fermilab, Jefferson
  Lab, KEK, SLAC
• The concepts presented today represent the work
  of many people at these laboratories
• Previous input from industry for the TESLA effort
  and for LHC is also important

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1.3 GHz, 9 cell, Nb RF Cavity
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TTF cryomodule
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Module end
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Generation 4, T4CM
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ILC cryogenic system overview (main linac)

• Revising and resizing the TESLA cryogenic concept
• Saturated He II cooled cavities _at_ 2 K
• Helium gas thermal shield _at_ 5 - 8 K
• Helium gas thermal shield _at_ 40 - 80 K
• Two-phase line (liquid helium supply and
  concurrent vapor return) connects to each helium
  vessel
• Two-phase line connects to gas return once per
  module
• A small diameter warm-up/cool-down line connects
  the bottoms of the He vessels (primarily for
  warm-up)
• Subcooled helium supply line connects to
  two-phase line via JT valve once per string (12
  modules)

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Sloped system concerns

• Want heat removal without bubbling or boiling
• Saturated superfluid heat flux limit about 1
  W/sq-cm
• 54.9 mm dia down-pipe means 23.7 sq-cm or about
  24 W per cavity can be transferred away
• But a claim was made that surface area limit is
  1/10 of that, 0.1 W/sq-cm, so 2.4 W/cavity limit
• Hence, want to pool liquid in 2-phase pipe by
  means of dams in order to provide large surface
  area for evaporation
• Conclusion in subsequent discussions -- dams not
  needed
• Even just 2.4 W/cavity is enough, expect 1.7
  W/cavity at 36 MV/m
• Most experience does not support the claim of the
  surface area heat flux limit
• Sloped system should not be a problem, within
  limits
• LHC will run some areas with 1.2 slope
• DESY will test sloped modules for XFEL

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Module heat estimates
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Module predicted heat loads
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Module pipe sizes increase
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(Increase diameter beyond X-FEL)
(Increase diameter beyond X-FEL)
(Review 2-phase pipe size and effect of slope)
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Cryo-string
Now 12 cryomodules per string, totalling 140 m
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Cryogenic unit 16 strings per cyrogenic unit,
so 192 modules per cryo unit (47 GeV)
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CERN LHC capacity multipliers

• Cryo capacity Fo x (Qd Qs x Fu)
• Fo is overcapacity for control and off-design or
  off-optimum operation
• Fu is uncertanty factor on load estimates, taken
  on static heat loads only
• Qd is predicted dynamic heat load
• Qs is predicted static heat load

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Cryogenic unit parameters
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Cryogenic unit length limitations

• 25 KW total equivalent 4.5 K capacity
• Heat exchanger sizes
• Over-the-road sizes
• Experience
• Cryomodule piping pressure drops with 2 km
  distances
• Cold compressor capacities
• With 192 modules, we are hitting our plant size
  limits, cold compressor limits, and pressure drop
  limits

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Cryogenic unit segmentation and other cryogenic
boxes

• Segmentation issue is ultimately tied to
  reliability
• BCD should include features for vacuum
  segmentation
• Assume 4 cryo strings (48 modules, 563 meters)
  per segmentation unit
• Cryogenic string supply and end boxes, which may
  (should!) be separate from modules, are also
  required within the ILC lattice

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Full segmentation concept (ACD)

• A box of slot length equal to one module
• Can pass through cryogens or act as turnaround
  box from either side
• Does not pass through 2-phase flow, so must act
  as a supply or end of a cryogenic string
• Includes vacuum breaks
• May contain bayonet/U-tube connections between
  upstream and downstream for positive isolation
• May contain warm section of beam pipe
• May also want external transfer line for 4 K
  standby operation (4 K only, no pumping line)

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Lengths and packing factor (from spreadsheet
originated by Chris Adolphsen and revised by Tom
P.)
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Cryogenic unit packing factor

• About 0.7 active RF length/total length
• Cryo boxes can be very short along the length of
  the linac if they have appendages to the side for
  valves, heat exchangers, liquid helium
  reserviors, etc. But these then require alcoves.
  Is this better than running the TBM slightly
  further?
• Cryo boxes can be incorporated into modules,
  improving the packing factor, but creating dozens
  of odd and special modules. (We are keeping
  cryogenic boxes separate.)

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ILC 500 cryogenic system overview for main linacs

• 10 large cryogenic plants (5 per linac)
• Approximately 2.3 km unit lengths
• Each cryogenic plant of about the maximum size --
  equivalent to about 25 kW at 4.5 K
• Each plant about 5.2 MW wall plug power
• ILC 500 main linac cryogenics about 52 MW total

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ILC cryogenics is more than these main linac
cryogenic units

• ILC will have many other cold devices other than
  these regular linear patterns of main linac
  cryogenic modules
• Most work so far has focused just on a simplified
  view of the main linac cryogenics

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Cold devices

• 940 main linac modules per 250 GeV linac (so 940
  x 2)
• Pre-accelerators up to 5 GeV (2 of these)
• 10 special low-energy magnet/RF modules (x 2)
• 61 standard modules, equiv to 5 strings (x 2)
• Damping rings (1 electron, 2 positron)
• Electron side -- 650 MHz SRF, about 15 cavities
  plus 200 m of CESR-c type SC wigglers 1200 W
  total at 4.5 K
• Positron side -- 650 MHz SRF, about 10 cavities
  plus 200 m of CESR-c type SC wigglers x 2 rings
  2000 W total at 4.5 K
• 200 meters of SC undulators in electron linac
  (300 W)
• SC magnets and crab cavities in interaction
  regions
• Various cryogenic feed, end, and transition boxes
  
• Several km of cryogenic transfer lines

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BCD Description -500 GeV Layout- (Slide lifted
from Positron Source Configuration by KURIKI
Masao and John Sheppard, January 2006.Cryogenic
device description in red added by Tom Peterson)
Up to about 500 MeV via special SRF cavity/magnet
modules totaling about 25 m x 20 MV/m Then up to
5 GeV with 21 standard SRF modules
650 MHz SRF, about 10-15 cavities plus 200 m of
CESR-c type SC wigglers, all 3 damping rings
SC magnets and crab cavities (no
quatities yet)
Standard modules (starting at 5 GeV)
Standard modules
RTML includes SC solenoids plus 61 SRF modules
RTML includes SC solenoids plus 61 SRF modules
200 m of SC undulators
Up to about 500 MeV via special SRF cavity/magnet
modules totaling about 25 m x 20 MV/m Then up to
5 GeV with 21 standard SRF modules
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Cryogenic system intertwined with linac lattice
and conventional facilities

• For example, warm beam tube sections could go
  into segmentation boxes
• Conversely, we would try to locate breaks in
  the cryogenic system at interruptions in the
  lattice
• Some flexibility with respect to unit lengths and
  segmentation lengths
• RF unit of 3 modules should not be broken
• Prefer to keep cryo strings (12 modules)
  unbroken, but a 9 or 15 module string is possible
  
• Can try to locate plants at other above-ground
  facilities

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ILC cryogenic system inventory
Since we have not counted all the cryogenic
subsystems and storage yet, ILC probably ends up
with a bit more inventory than LHC
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Cryoplant concept
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Size comparison to TESLA TDR

• TESLA 500 TDR had 7 large cryoplants
• 5 at about 5.2 MW and 2 smaller
• ILC 500 looks like about 12 large cryoplants
• 10 at about 5.2 MW and 2 smaller
• Dynamic load up with gradient squared (length
  reduced by gradient), larger multipliers, lower
  plant efficiency
• Costs increase roughly linearly with increasing
  cryoplant power when we are pegged at the 25 KW
  plant size.
• Increased heat means adding plants, shortening
  strings, etc., so not the 0.6 or 0.7 power
  correlation with power at these levels of load.

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ILC cryogenics -- open issues

• Cryogenic loads outside of the main linac
  cryomodule strings (magnets, DR RF, etc.)
• Multiplier factors for sizing system
• High flow rates (about 50 times TTF flows)
• Segmentation philosophy (minimal or more)
• Reliability estimates
• Trustworthy predictions for module strings will
  require more experience with this technology
• LHC experience will tell a lot about reliability
  of a large-scale 2 K cryogenic system similar to
  ILC
• Upgrade heat loads and scenarios
• At 35 MV/m estimate 50 more heating

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References

• TESLA TDR -- online as TESLA Report 2001-23 at
  http//tesla.desy.de/new_pages/TESLA/TTFnot01.html
  
• Navigate to other TESLA and TTF documents going
  back to 1993 from the same web page
• ILC BCD documents
• http//www.linearcollider.org/wiki/doku.php?idbcd
  bcd_home
• bcdmain_linacilc_bcd_cryogenic_chapter_v3.doc
• ILC presentations
• Navigate from ILC home page via Calendar/Past
  Events and Calendar/GDE Meetings
• http//www.linearcollider.org/cms/?pid1000012