Tilt angles reloaded, and status of some other things

2

Overlap definition

• Assume 5mm Si separation, 95mm active width.• Require 4 hits for 1GeV/c particles in 2T.• Study overlaps from 0 (hermeticity) to 10mm overlap.

2

Active width (95mm)

1GeV

/c tr

ack

Overlap

Si separation (5mm)

3

Radii

• Overlaps achieved by changing radii (for innermost) or number of staves (for outermost, 5mm overlap is 4 staves).– This gives discrete possible radii which might not always be optimal.

• Strawman is based on hermeticity + next multiple of 4.• For innermost layer 1mm in radius means ~200µm in overlap.

5mm overlap 10mm overlap0 overlap

4

Overlap and material

• Assuming no material change per stave (material reduction only due to smearing over smaller area, or more staves for similar radius).

• 1mm overlap corresponds to ~1% in radiation length (makes sense, active width is 95mm…)

4

55

Tilt angle and material

• Assuming no material change per stave (material reduction only due to smearing over larger area).

• Change of tilt angle by 1° corresponds to ~1% less material.• That’s small for small angle variations, but 5° might be worth the

effort.

66

Definition of envelopes

Active width (95mm) Half envelope height(Maximum when envelopes touch)

Wedge length(centerline extension until

next envelope hit)This wedge would have to contain •Module dead edge,•Additional core width, •edge electronics,•locking mechanics.

77

Envelopes

• Innermost and outermost barrels are not very different in envelope height (but outermost barrels have more room in width).

• 1mm half height (ie 2mm overall stave thickness) increases minimum tilt angle by ~1.5° (NB this is what the US locking mechanics needs).

• 5mm additional overlap reduces max half height by ~2/3-1mm in (increases minimum tilt angle by ~1-1.5°).

• For 10° tilt angle stave + envelopes must be less than ~15mm (for 2mm overlap).

8

Edge envelopes• Space on the inner edge is limited

– This is definitely true for outer surface, but even on lower surface it is likely to be limited due to locking mechanics.→ All large edge components (powering etc.) should go on outer edge→ Tape area (bond connections) should be traded off from inner edge to outer edge (a priori the modules does not

need to be symmetric on the core)

• Example: Limit to plank overhang (assuming 5mm core)

8

9

Tilt angle and performance

ATLAS testbeam paper

Charge sharing improves resolution…Do we not want to tilt modules by about 10°?

80µm/√12

10

Tilt angle conclusions• Lorentz angle argument seems to be weak

– Resolution improves by about 1% for each ° off Lorentz angle.– Occupancy increases by about 1% for each °.– Lorentz angle is expected to range over lifetime from about 13-

16° to 4-6°.• Material argument not much stronger

– Relative material increases by about 1% per ° of tilt angle.• Agreement seems that hermeticity for 1GeV/c tracks is

sufficient (with some overlap to keep tolerances low).– I suspect this is 1-2mm.– Relative material is about 1% per 1mm overlap.

• All these issues are most pronounced in the innermost layer (where space is the most constrained)

• My conclusion: We should shoot for 10°, but relax if difficult, also not a big design discriminator.

11

Co-curing update• Doing co-cures for electrical studies (does performance suffer from

co-curing?)• K13D2U/RS3 with special test tapes (similar build-up as real tapes)• 1 co-cure in press: perfect• 2 co-cures in autoclave with convex jig, tape up

– First:• ramp p and T down in parallel• Crease in CF at z~1000mm. Fibres broken.• Interesting to see if electrical damage…

– Second:• New Teflon coating on jig, New post-cure procedure (Ramp p down first,

open bag, then ramp down T)• Worked fine

• 1 co-cure in autoclave with concave jig, tape down– This apparently worked fine (CF is well compacted)– Some creasing of tape where we taped it to the jig to avoid glue creep.– Will try to freeze this tape to make sure it’s ok.

• Will compare tape length expansions before electrical testing.

12

Locking points• Lots of progress, ongoing discussion, group effort

– Simplification (cam or screw): push to reduce to 2 parts

– Improve action on bracket (pull-in rather than push-out)

• Together with rotating insertion rails we have made a lot of progress in the last months…

• I’m optimistic that we will arrive at a very elegant system fairly soon.

13

ESPI

• CF base plate is installed (locking points not yet mounted)

• When operated at ambient there is a small number of fringes– Not yet understood

• Next measure base plate in cold environment, then mount locking mechanics.

• Thermo-mechanical stave is at Oxford.