NLC - The Next Linear Collider Project
Knut Skarpaas VIIIMay 1999
Engineering aspects of the Detector interface
Knut Skarpaas VIII
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Detector interfaces
• Collider hall
• Final magnet supports
• Assembly Sequence
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Collider Hall Geometry• Detector Size
– Currently modeling structure for small US design
• Small detector has a strong following– Magnet support for last quads fairly rigid
– Compact package reduces deflections
– Detector group is further along on this design» We are in continuous contact with many of the detector
working groups
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Collider Hall /Detector Assembly Procedure
• Assembly staged during beamline commissioning• Must shield detector assembly area from the beam
• Movable barrier
• Temporary support for beamline– Must act like detector
• Final focus assembly dependent on magnet support method
• Cantilever
• Support tube
• Access to Detector Sub-components– Vertex detector
– Central tracker
• Endcaps may be captive– Segment endcaps
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Magnet support options
• Design goals for various support options– Minimize deflections
• Minimize unsupported span
• Put support near critical deflection points
• Put support near massive items– Current cantilever option has support near mask centroid
• Maximize moment of inertia (minimize sag)– Tubular support advantageous
• Will need access ports to work on / install magnets
• Minimize mass supported by tube• Some mask forces may be transferred to the doors
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Design goals for various support options cont.
• Material requirements– Minimize radiation length of material near Interaction Point
• Cantilever design has no material at IP
– Radiation hard design
• Adhesives / polymers may degrade
• Interface with required detector components– Vertex detector in bore (if support tube)
• If cantilever, support vertex detector from mask tips or from central tracker
– Masks (held by cantilever or inside support tube)
– Tungsten masks are massive
• 2500 lb requires support for door opening
– Central tracker hugs outer bore (or masks)
– Pass through steel in door
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Design goals for various support options cont.
• Door opening to be minimized to reduce Br near quads• Clearances
– Assembly clearances
– Allow for gravitational deflections
– Current cantilever deflects .16” with door open
– Seismic clearance
• Site specific
• Services– Vertex cables in bore (if support tube)
– Cooling for vertex detector– Vertex detector requires 170k nitrogen gas– Foam or vacuum insulated lines
» Foam lines are large (2”)
– Luminosity monitor cables / cooling
• In bore for most options
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Assembly sequence
• Must be able to put detector together first time• Must be able to access various components for
servicing• Minimize time to get to buried components
– Vertex servicing
– Central tracker servicing
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Allow for magnet positioning
• Coarse adjust– First time alignment– Remote alignment to remain within fine adjustment range
• Magnet Coarse Adjustment options– Actuation
• Screw• Ramp• Cam• Bellows or piston with liquid or gas• Piezo
– Drive style• Motor (stepper or servo)• Can not be used in high magnetic field• Drive shafts can transmit torque into bore
– Wind up problems can be eliminated with proper gear boxes– May contribute too much heat / vibration
• Motor (hydraulic / pneumatic) (rotary or linear)– Seals may be a problem in high radiation areas– Gas may be too compressible– Hydraulic fluid may not be radiation hard– Vibration and heat can be low
• Peizo – Stroke may not be sufficient for the coarse adjust
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Fine adjust
• Get to final magnet location
• Active positioning– Needs to be radiation hard
– Non-magnetic
• Fine Adjustment Options– Due to the fast response, and non-magnetic properties of piezo
electric actuators, this is our current choice
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Interferometer compliant
• Several configurations possible– Maximize stability / minimize detector penetrations
• Holes / windows in support allow sight to magnets
• Vacuum / gas transport lines– Vacuum requires a joint to the stabilized object
– Transport lines can transmit vibration
– If vacuum is used with windows, windows may shift beam
– Gas is nice, but index of refraction changes with temperature
• Heat from electronics may shift beam
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Support tube:
• Tube passes through detector– Support styles possible:
• Simple – Simple– Deflection is maximum & stress is high in center
» The center is a bad place for high stress since it has a smaller moment of inertia and requires minimal material
• Fixed – Rolling– Deflection is smaller & stress is high on ends
• Fixed-Intermediate Support- Intermediate Support-Rolling– Tricky stress allocation
– Central tracker group does not like this option
• They would like to put detectors near the inner masks
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Cantilever:
• Tube is installed from each tunnel
• May be mounted to a pier extending into pit– While running, support is near mask CG
– Simple – Simple
• Deflection is maximum when door is open– Deflection good while running
– Fixed – Simple
• Deflection is smaller but stress is high on one end
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Detector / final focus options:
• Option 1– SLD style detector
• Pro: Quick access /easy detector shapes
• Con: Large pit / unstable magnets
• Option 2– SLD like detector with reduced door opening
• Concrete pillar under magnets (except last 2)
• Last 2 magnets on short cantilever or held by door
• Door supports trimmed on outside (doors may need counter weight)
– Pro: Quick access /easy detector shapes» All but last two magnets are on “bedrock”
– Con: Last magnets rely on detector for stability (but could be actively isolated)
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Detector / final focus options cont.:
• Option 3• BaBar like detector split door
– Concrete pillar under magnets (except last 1)
– Cantilever last magnet and mask
– Door supports trimmed on outside (doors may need counter weight toward IP)
• Pro: Quick access
• Con: ECAL and HCAL must be split to remove (may require difficult rigging)
• Option 4– SLD like detector (cut off outer feet)
• Key shaped pit
• Roll detector to open
• Fixture to open (to hold cantilever)– Pro: Stable / all but last magnet on bedrock – Con: Complicated pit / many cables to deal with / vac. dis-connect– Long down time to get to vertex detector
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Detector / final focus options cont.:
• Option 5– Central detector spool package with Small detector layout
• Top splits in middle (iron and HCAL move to sides)
• Spool cranes out
• Shake spool– Pro: Stable
– Con: Complicated pit / hard to get inside spool / vac. dis-connect / tricky wiring
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Assembly Procedures (Small detector / cantilevered supports)
• Assemble detector on shielded side of pit– Beam line commissioning happens using the real doublets on the
other side of the pit with a temporary support
– Remove EM magnets on pier and pull doublet back into tunnel
– Rotate the detector to become parallel to the beam line
– Roll the detector into place (including doors)
– Slide cantilevered support tubes through doors
– Make up vacuum and transfer load of masks from detector to the support tube
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Vibration Issues
• Since the extent of vibration amplification varies widely with various geometries, emphasis until this point has been put on solidifying the detector geometry– Detector revisions occur biannually
• As detector shapes and magnet styles become more stable, vibration isolation methods will be explored further– Several possible vibration isolation scenarios are being considered
– Under all conditions, local noise must be isolated from the detector
• Local traffic minimized
• Pumps on isolators on separate slabs
• Well thought out plumbing and other services
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Vibration Issues Continued
• Find a stable site and make all components rigid– Many problems could arise if we do not have a “Plan B” (and the site becomes
noisy)
• Have a rigid detector and a floating (active / passive / both) magnet support
– A permutation of this option may be the most practical for a large detector
• Float the entire detector (or a large portion of it) on a gas suspension system
– A possible air system has been considered which incorporates a variable natural frequency which allows adjustment for detector mass changes
• Communication has begun with the LIGO group– Work is currently being done at LIGO to stabilize a several hundred kilogram mass
to 1 nm– The LIGO system currently stabilizes a mass to a level several orders of magnitude
better than NLC requirements. However, the system used is not currently practical for a physics detector. (Their frequency requirements are also different)
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Thermal Issues
• A high degree of positional stability requires a thermally stable environment– Detector will most likely be under a thick (~6’ thick) concrete lid
for radiation protection reasons
• Large thermal masses should aid thermal stability
• Thermal excursions happen slowly and require a coarse adjustment range for the movers
• Tunnels which connect to pit are fairly cool at this point– Should not be a large heat source (and may be sealed from pit)
– Tunnel temperature is set by local cooling tower capacities
• Have looked at wet bulb maximums at several sites
Knut Skarpaas VIII
May 1999Slide #
NLC - The Next Linear Collider Project
Conclusions
• Detector design is still undergoing changes
• We are in contact with key people in many detector working groups
• One of the more popular detector choices is being structurally modeled currently
• Several issues will be studied and prototyped in the near future– Vibration isolation options will be pursued