Engineering aspects of the Detector interface

NLC - The Next Linear Collider Project

Knut Skarpaas VIIIMay 1999

Engineering aspects of the Detector interface

Knut Skarpaas VIII

Knut Skarpaas VIII

May 1999Slide #


Detector interfaces

• Collider hall

• Final magnet supports

• Assembly Sequence

Knut Skarpaas VIII

May 1999Slide #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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 #


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

Documents

Engineering aspects of the Detector interface