Ilc main Linac Design Status

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ILC Main Linac Design Status


  • -MPY-

  • Bangalore 9.3.2006

  • General layout

    • Cryogenic layout
      • Module layout
      • Segmentation
    • Tunnel sizes


Main Linac: Towards an Reference Design Report (RDR)

  • Since Frascati and the appproval of the BCD several things happened in the main linac layout to get the RDR done

    • Must-link by C. Adolphsen:
      • Main Linac RDR Wiki:
    • Cryomodule & Cryogenics Groups are defining cryomodule length and cryoplant layout
      • First pass generated at Jan 16-17 CERN meeting, has since been updated
    • RF Group to work with Civil Group to define the size/layout of support tunnel
      • Some detailed analysis is under way – diameter is going down again…
      • Alternate cross section?
    • Magnet group with specifying the linac quad and corrector package
      • Reviewing issues
      • Seperated corrector design

RDR Linac Definition (Cont)

  • LET Group has been working resolving beam dynamics related issues at Feb 8-11 CERN meeting

  • Work with Instrumentation Group to define diagnostics

    • List of instruments and issues generated at Jan 17 FNAL meeting
  • Discussing implications of MPS and availability requirements with Himel et al.


  • Must-read by T. Peterson:

    • Cryogenics is not only the main linac….
  • Heat load revisited

    • More conservative estimates of static heat leak than in TDR
      • based on TTF measurements (where all module have a warm-cold transition)
    • Higher dynamic load due to higher gradient
    • Keeping the plant sizes below 25 kW total equivalent 4.5 K capacity leads to maximum plant spacing of ~2.3 km
  • Cryo-segmentation every 560 m – warm or cold?

    • Use segments to isolate insulating vacuum sections
      • Not necessarily a warm-cold transition
    • Introduction of a cold-warm transition could be used for shortening regions that are warmed up for repair work
      • Faster cooldown
      • Could be used for Instrumentation and MPS
        • From the beam dynamics standpoint not absolutely needed
    • Main disadvantages are
      • cost
      • contamination issues
      • increased vulnerability to insulating and beam pipe vacuum failures
        • MPS issue

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)

Lengths and Packing Factor (from spreadsheet originated by Chris Adolphsen and revised by Tom Peterson)

Towards an ILC Cryomodule (4th generation)

  • International Effort between the three regions

  • Design changes are towards nailing down slot length of components

    • Costing should be straight-forward from TTF (and possibly XFEL) experience

ILC Cryomodule Design Considerations

  • Move quad package to middle of cryomodule to achieve better support and alignment.

  • Shorten cavity-to-cavity interconnect and simplify for ease of fabrication and cost reduction.

  • Overall improved packing factor.

  • Simplify the assembly procedure.

  • MLI redesign to reduce hands-on labor costs.

  • More robust design for shipping.

  • Reliability of tuner motors in cold operation.

  • Revaluate cryogenic pipe sizes

    • partially done for the XFEL already

E.g.: Module pipe sizes increase (T. Peterson – CERN Meeting)

Inside an ILC cryomodule

  • Cavity package

    • Cavity
    • High power RF coupler
    • Tuner
    • Magnet package
    • …(time won‘t permit)

Cavity with Frequency Tuner

  • No BCD Tuner, some designs are very close to requirement

    • Generic issue to all designs: motor and piezo reliability
    • Deemed to be feasible, but some R&D needed
  • E.g Bladetuner

    • Issue with cavity’s magnetic shielding
  • Could be also another tuner that does not need inter-cavity space

    • Just watch out for the cryo-lines…

Flange/Bellows Design Specs:

  • Flange/Bellows Design Specs:

  • • Bolted flange (12 bolts/flange)

  • • Convoluted SS Bellows (10 waves, 54mm free length, ±25mm)

  • -Length of bellows dictated by bolt length, old elastic parameters

  • • Bellows elastic requirements: ±4mm (~1mm thermal + ~3mm tuning)

  • • Aluminum Alloy 5052-H32 Diamond Hex Seal

  • • 7 Ton clamping force, 35 N-m torque/bolt

  • • Mechanical analysis done @ Desy, INFN (Cornelius Martens, Roberto Paulon)

Proposed Cavity Layout

BCD assumes use of XFEL Main Coupler

ACD: Seperate Quad Cryo-section

ACD: Pros / Cons for a Separate Quad/BPM Cryostat

  • Pros

    • Allows for a common cryomodule design
    • Flexibility
      • Accommodation of different magnet packages, upgrades, etc.
      • Independent adjustments to the quad/BPM position
    • Handling
      • Allows independent cold testing and measurement of the magnet package
      • Schedule, resources, and fabrication facilities not tied to mainstream cryomodule production
    • Precludes the need for independent quad movers inside the cryomodule (ACD)
  • Cons

    • Design issues
      • Interconnect forces due to bellows could affect quad alignment
      • Vibrations due to interconnect might need crosscheck
    • Cost
    • Potentially requires more longitudinal space required in the lattice

Region between Cryomodules

  • Assume 850 mm Flange-to-Flange length (TTF)

    • 850 mm between flanges, 815 mm ‘free’ space
    • Length partially defined by requirements of cryo tube welding and beam tube assembly (local cleanroom)
  • Includes

    • 270 mm Broadband HOM absorber
      • XFEL design could be used (but likely over-designed)
    • Manual Gate Valves
    • Pump-out Ports (integrated in absorber)
  • Needs to be better defined

Some critical design issues

  • ILC specific issues

    • Quad/corrector/BPM package needs more work
      • Implication for the next generation cryomodule (type 4) that is being developed by FNAL/INFN
    • Cavity-to-cavity interconnect design.
    • Magnetic shield re-design.
  • Issues for both ILC and XFEL

    • Tuner reliability, slow and fast.
    • Vibrational analysis, which will be compared to measurements for verification of the model for future design work.
    • Development of module and module component tests.
    • Design of test instrumentation for the module.
    • Verification of cavity positional stability with thermal cycles.
    • Robustness for shipping, analysis of shipping restraints and loads, shipping specifications.

RF System: RF Unit

    • Solid-state switched modulator with 1:12 step-up transformer and bouncer droop compensator
    • 10 MW 1.3 GHz multi-beam klystron
      • Currently do not have a robust tube design
      • Assume horizontal mounting (could be vertical depending on tunnel height) – no such tube built yet.
    • Waveguide distribution system with three way split to feed 24 cavities – each feed includes isolator and phase shifter / Qext controller.
    • 680 RF units for cold cavities in ILC 500
    • Modulator, Klystron and three-way splitter in support tunnel, rest in accelerator tunnel.

Examples of RF three-way split

TTF Waveguide Distribution

Need more compact design (Each Cavity Fed 350 kW, 1.5 msec Pulses at 5 Hz)

RF System Design

    • Work so far on
      • Understanding interface to LLRF system, which is in the Control’s group domain
      • Compiling list of actuators and signals to be monitored in the linac
      • Working with civil group on rf system layout in the support tunnel
    • Distribution system needs more design work to lower cost

Example: RF System layout

Example: Implementation using ATCA standard

Civil Facilities: Tunnel Layout

      • Distance between tunnels based on construction needs, radiation protection is under investigation
      • Water influx
      • Tunnel Sizes
        • Component lists with sizes generated
        • The 4 m diameter support tunnel and 3.2 m diameter beam tunnel in BCD are likely too small
        • Would help to make components narrower – work in progress
      • A lot of work underway on other details
        • Water and power distribution
        • Air supply and temperature regulation
        • Penetration size and access (e.g. crossover)
        • Transportation and stay clear
        • Personnel access and egress
        • Fire Safety

Tunnel layout: Component Lists

Example: 4.5 m Linac and 5 m Service tunnel

Service tunnel sizes under discussion: 4.5m, 5m and 5.5m

Crossovers between the tunnels

Diagnostics: Under discussion

  • Aim for BPM resolution of 0.3 micron at full charge and 3 micron at reduced charge (10%) when running with keep-alive source. Want to achieve this bunch-by-bunch with bunch spacing down to 185 ns.

    • Accelerator Physics might be satisfied with less ambitious goals for full charge (~1um)
  • Do not implement HOM readout initially, but to bring signals just outside of the cryomodules where they would be terminated.

  • Use beam coupling to HOM ports to monitor relative bunch intensity and bunch phase relative to rf (use for rf phase control)

  • Optional: Include 6-12 m long warm sections after every 48 cryomodules (560 m)

      • Use for beam line and insulating vacuum isolation.
      • Each would contain a laser wire: with 21 wires, have 7 independent measurements of emittance along each linac.
      • Could contain other instrumentation such as beam halo and dark current monitors.
      • Could contain spoilers for short-train beam abort.
      • Could be used for cryo-segmentation as discussed earlier
      • Penalties (as mentioned before): Cost; MPS issues, contamination
  • Within linacs, measure beam energy and energy spread only for the electron beam in the undulator line.


  • Many discussions on-going

    • Interplay between Area systems and Technical systems is being defined and starts to work
  • Very detailed information becoming available

    • Cryogenics
    • Module layout
  • More work needed

    • Tunnel layout has changed and experts are working e.g. on the component level to further reduce the tunnel size
    • Costing details need more work:
      • E.g. How to handle TESLA TDR or XFEL cost estimates?
      • Is there a ‘common sense‘ to do the costing?
  • Baseline design exists

    • Some of the options need more thorough discussion e.g. cryo segmentation

Thank you…

  • … to the many colleagues who provided me with transperencies!

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