Background to the current problem

1. As a result of the high stresses in the bobbin due to the magnet load, the bobbin end plate needs to be increased. A 10mm increase was requested and granted;

2. It was understood that the 10mm space could be found by reducing the gaps between the bobbin end plate and the magnet cryostat which are within Tesla scope of supply. In hind sight, we should have been more cautious when granting the request;

3. It was subsequently noticed that Tesla had intruded on the space originally allocated for KEK for the LH2 piping connection as well as expanding on the gap space between the bobbin end plate and the vacuum cryostat. This was not apparent when looking only at their 3-D models;

4. The space in this area is so tight that even without any of these increases, there is literally no gap between the outer surface of the Large end plate and the flange face of the Vacuum vessel. Any item sticking out of the vessel flange will have an effect on the installation of the AFC modules when slid in from the side

5. The following slides explain in detail the problem and our proposed solutions.

13.5

7.0

25.0

2.05.0

309.5

47.5

39.0

12.5

422.0

bobbin

Thermal radiation shield

Magnet cryostat

Large End Flange

386.0

362.0

24.0

The leading dimensions shown on the interface drawing to both KEK and Tesla

9.4

14.5

35.0

4.05.0

309.5

32.1

39.0

12.5

422.0

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

386.0

377.4

8.6

Fo

ul!!

Foul between LH2 pipe and magnet cryostat !!!

The design as it stands

9.4

14.5

35.0

4.05.0

309.5

32.1

39.0

12.5

422.0

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

386.0

377.4

8.6

Hydrogen Absorber and the feed pipes are already made and tested. Cool down test has already started. It is not possible to make any change or modification on the pipe work arrangement on the Absorber. Spoken to Shigeru who confirmed that nothing could be done to change.

The constraint from KEK:

Constraint from Tesla:-

Tesla needs 10mm for the extra thickness for the bobbin end plate. They also increased the gap at and thicken up the thermal radiation shield sheet metal from 2mm to 4mm. (Are these absolutely latter necessary?)

Fo

ul!!

The design as it stands

The Solution

9.4

9.0

35.0

4.0

5.0

310

47.5

39.0

2.5

422.4

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

386.0

372.4

24

10.4

This solution is to shift the absorber upstream by 10.4mm

0.4mm

Large End Flange locally thinned down to 2.5 mm

DRAWING 2009/4/28

by

Shigeru Ishimoto

Shigeru’s comments:

ALL DRAWING

AFC with ABSORBER

AFC with ABSORBER

Close-up

AFC with ABSORBER

Close-up

Absorber Support Flange

Plan-2

Changes to be made based on Plan 2 of Shigeru’s comments

This drawing has now been submitted to Tesla for modification

This section of the Large End Plate is thinned down locally to 2.5mm

Mike Zisman’s comments / suggestions

I think there is a plan now, with one major  "variable."

1.It seems pretty clear that we can thin out the end flange locally to accommodate the pipes. The issues here are how much space must be thinned out and what this does to the strength of the end flange. Wing can answer the latter question via FEA, and Shigeru needs to be involved in determining how much space is adequate (he apparently prefers a somewhat larger area than Wing has suggested). This looks straightforward to me.

2.Tesla has agreed to pull back the envelope by 4.5 mm or so, as reported by Wing. We need to check that this does not compromise the thermal properties of the FC, i.e., that Tesla is not being forced into an untenable design position. If they are, this problem could escalate into a big deal.

3.The variable is whether we fix absorber 1, which is already built. I favor doing so, but it is pretty clear that the experiment could survive without doing so if need be. So, this becomes a judgment call based on cost, risk, and schedule. An alternative here is to build a fourth absorber, and treat the first one as a spare, to be used only in an emergency. Then there are three identical units and one that is off by 10.4 mm if we need to use it (or to be used for system tests only). It does not seem like we are under time pressure with the absorbers, so either fixing item 1 or building item 4 seem viable from a schedule viewpoint.

Oxford’s answer to Mike Zisman’s 1 st comment (FEA assessment of the thinned down effect:-

Applied pressure:- 1 bar

Local peak stress:- 90.5 MPa

Max. bending stress:- 62 MPa

Pro-rata to the design pressure of 1.5 bar (Table 1.8 of tech,spec), the max. bending stress = 93 MPa.

Allowable bending stress for Al T6061 at room temp = 1.5 x 78 = 117 MPa.

Stress in the thinned down area does not seem to be affected – mainly because of the reinforcement effect from the rest of the plate which is 12.5mm thick.

This area has a thickness of only 2.5mm

End load effect (from Safety window) is accounted for and is applied onto this area

Summary of our proposal to the Technical Board for approval:-

1) KEK to supply a new absorber with extended LH2 feed pipe length to allow it to be mounted at its original position. That is, the horizontal feed pipes to be extended by 10.4mm;

2) The current absorber will be used as a spare item. This keeps all the absorbers in the cooling channel at the intended position;

3) Tesla to agree to reposition the thermal radiation shield and the magnet cryostat to those shown in slide 5. This leaves a gap space of 47.5mm for the LH2 feed pipes. Tesla will also check that this does not affect the overall heat leak / balance within this area;

4) Tesla to agree to machine two areas in the Large End Plate to reduce the plate thickness from 12.5 to 2.5mm. This makes room for the 10mm taken up by the increase of the bobbin end plate;

5) FEA assessment carried out by Oxford shows that the stresses in the Large End Plate is acceptable even after local thinning;

6) Cost and Schedule implication from Tesla has not been received. However, they have been asked to submit one.