indico.cern.ch · Created Date: 10/2/2019 9:07:14 AM

Technical Review of D2 short model CERN 2 October 2019

Technical review on D2 short

modelCERN 2 October 2019

Last results on D2 short model collaringP.Fabbricatore on behalf INFN team

1. The collaring of the repaired V2 aperture

2. Delamination of the G11 end spacer in the pole

3. General considerations about collaring

4. Coil dimensions – polymerization shims


Among the actions taken for

mitigating the problem at the

origin of the conductor

damage, the collars in the LC

side of aperture A has been

changed for including the

noses in the collars.

Replacement of coil A in aperture V2 of D2 short

model

• Following the problem met with the coil

A of aperture V2 limiting the current at

about 10 kA, the aperture was

uncollared and a damage of the

conductor found on the electrical exit

placed on the pole.

• A new coil type A was built and a new

collaring of the aperture V2 took place

V2 A3-A4

V2 A2-A3

V1B

AV2

A

B


After collaring there was a clear evidence of a damage of the end spacers

placed in the pole at the connection sides as shown in figure for the

(new) coil A type (the damaged zone is circled). The coil B of the aperture

shows the same kind of damage in the same location (the end spacer

placed in the pole) but of quite reduced amount

After re-collaring V2


After inspecting the collared coils

(also the one of aperture V1) we

have realised that in all cases there

are signs of de-lamination in these

spacers mainly due to the presence

of a hole weakening the

components. In the present case of

the recollared aperture V1 the

damage is more pronounced

because with the new collars having

an integrated the stainless core

embedded into the pole spacer is

no more present (this core was part

of the separated nose as shown in

the following figure showing the

non-connection side of new Coil

type A ).

Evidencies of delaminations in the pole spacer


The repair was done on

August 8th in presence of

INFN personnel. As already

remarked, the most damaged

pole end spacers after

collaring was the one of coil

type A (the new wound coil).

The inner part of the pole was

partially delaminated so first

of all ASG decided to remove

the part of the pole which was

already almost detached see

figure on the right (the thicker

part could be around 2-3

mm).

Repair of G11 poles in aperture V2


Repair of G11 poles in aperture V2

All holes and empty spaces of

that region with charged

stycast. The results for both

coil type A (left) and B (right)

are shown in the figures.

After the repair the electrical

tests (ground insulation, surge

tes, coil resistance) passed.

The magnet has been re-

assembled and ready to be re-

tested at cold

Technical Review of D2 short model CERN 2 October 2019 8

In the collaring phase the

upper and lower coils are

pressed each other through

their collars up to the caves

of the upper and lower collars

are aligned, allowing to insert

the keys and freeze the

aperture geometry.

The dimensions of the coil

should be such that when

keys are inserted the applied

pressure should guarantee

the designed pre-stress (with

some margin).

If coils (including ground

insulation) are thicker the

required pressure for

inserting the keys is higher. If

the coils are too thick, the

pressure can break the coil

Some general considerations on collaring


The new coil A was between 0.3 mm and 0.4 mm larger than nominal

(measurement under a pressure of 70 MPa) in line with the last coils done but

about 0.2 mm larger than the damaged A type coil. Moreover this time the

correct midplane insulation of 0.2 mm per coil was put in place (previously ASG

put 0.05 mm insulation causing b3 and b5 rising to +10 units). We have

observed that the dimensions of coils + midplane insulation has caused problems

in the collaring which has been done at a pressure 8% larger than the previous

collaring operations and only after long massage cycles. We have observed a

delamination of the poles in connection side

The coils are larger than nominal value at 70 MPa


The polymerization shims decided after tests on

stacks and mokeups

To be noted: shims fixed after test showed coilis -0.2 mm wrt nominal


Dimensions of coil A1 (the faulty coil)


Dimensions of coil A3-R (replacing the faulty coil)

Using the same polimerization

shim, the coil dimensions in

the central region changed

from + 0.26 mm deviation to +

the 0.43mm

To be noted that the coil

copper wedges produced by

lamination are at the limit and

some time out of tolerances.

ASG think this was the reason

for the 0.2 mm dimensional

variation among coils,

However it is clear from these

results that the polimerization

shims shall be increased of

0.2 mm-0.3 mm


Tapered shims in the coil ends

• The coil ends are constrained by the

no-pole collars, which can in principle

press this region only if the azimuthal

dimension is increased.

• In order to have controlled

dimensions of the coil ends allowing

to have a determined azimuthal

stress, tapered shims are placed at

the midplane

• The maximum thickness of the shims

is at the coil ends, reducing

progressively to zero longitudinally

along the coil end (about 150 mm)

• We think that the tapered shims were

too tick (see Stefania’s presentation)


1- The coil azimuthal dimensions involved in the model

were too large ( from 0.26 mm to 0.43 mm larger than

nominal) The polimerization shim shall be increased

(see Stefania’s presentation for quantitative values).

Crucial test with the practice coil (preceded by tests on

short mokeups)

2- The pole and spacers shall be compact with no holes

weakening the structure

3- The mid-plane tapered shims put in the coil ends shall

be re-calibrated for avoiding pressure higher than 70 MPa

in coil ends.

Indication for the prototype


Thank you for your attention

indico.cern.ch · Created Date: 10/2/2019 9:07:14 AM

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