Continued Coil Autopsies - CERN

Continued Coil Autopsies

S. Krave, V Marinozzi, M. Parker, M. Baldini

24 March 2020

Coil S10 Comments and Autopsy

Coils P03 and P04 visual overview

Coil P04 Heater Autopsy

Moving forward…

2S. Krave | QXFS10 Autopsy

This coil was built to test “the swap”

• Place 1 layer of 5 mil glass under

the heater, and one layer over the

heater

• Normally no additional glass

between heater and coil

0 2 4 6 8 10 12 14 16 18

15500

16000

16500

17000

17500

18000

quenches

holding

Cu

rre

nt (A

)

Quench #

S. Krave | QXFS10 Autopsy 3

QXFS10 (MQXFSM2)

Heater to coil Hipot in air after cold test: first

failure

4

0 50 100 150 200 250 300 350

0

500

1000

1500

2000

2500

3000

3500

4000

# quenches req.

MQXFAP1 (coilP5)

MQXFAP2

MQXFS5

Long Mirror (coil P01)

MQXFS3 (coil8)

MQXFS1

MQXFAP1/AP1b (coil P2,P3,P4)

MQXFAP1b (coil P6)

MQXFSM2 mirror

He

ate

r to

co

il firs

t vo

lta

ge

fa

ilure

(V

)

# of quenches

He 150 K

He 300 K

HiPot req. after He

Mirror first failure

after cold test:

1 heater strip?

Test repeated: short

Coil Photos

5OD without Traces after Test

ID after Test

OD In

Impregnation

Tooling

OD After Test

• General Notes:

Coil OD appeared almost as new

• Very little cracking or delamination

present

• Nothing else to report

Hipotting after Disassembly. Heater

jumper removed

Heater 1, MP : Passed 6kV 1st try, 0µA

Heater 4, MP: Passed 6kV 1st try, 0µA

Heater 2, Pole: Passed 6kV 1st try, 0µA

Heater 3, Pole: HiPot fail, dead short ~2

MΩ

• Reported By Maria Previously


HiPot each trace

0

500

1000

1500

2000

2500

3000

3500

4000

1 6 11 16 21

Hip

ot

Failu

re V

olt

age

Hipot Voltage Failure Index

1st Hipot Failure Region Voltages

QXFP01 Heater 2

QXFP01 Heater 3

QXFP01 Heater 4

QXFS10-3

QXFS10 data point overlaid on

QXFP01. Note that on QXFP01,

hipotting stopped at 3680V

3720 V

Procedure:

1. Attach multimeter to monitor

resistance of short. A graph is an

excellent feature.

2. Turn can of air over (or use freeze

spray) and gently apply cold to

heater trace.

3. Slowly move from one side to the

other noting changes in

resistance.

4. If change is found, mark area and

see if it repeats.

This took 52 seconds to find short

within 10 mm…


Locating Short: Canned Air Along the Problem Heater

1. Score around heater

2. Cut and peel back

glass

3. Lift heater

4. Verify short removed

5. Cut heater and re-test

(HiPot) remaining

segments


Removing short (as before)

Detail of the Hipot Failure Location

S. Krave | QXFS10 Autopsy9

This looks familiar…


Bubble Map roughly to scale

Bubble size represents relative area

of region. This dot is ~125 mm^2

Bubble Color Key

Passes 3680V Hipot

1500V Hipot Failure

2590V Hipot Failure

3680V Hipot Failure

HiPot Failure at 3720V. This would

have counted as a pass.

• There is an extra layer of glass

between this coil and the heater

trace

• Similar behavior is noted in the

polyimide of the trace as without

extra glass

• Small bubbles in the trace

adhesive, as before

• Distinct striation in internal

blistering, likely caused by

repetitive quenching


Notes

9 distinct striations ~8 distinct striations

QXFP01

QXFS10

After Identification of 1st failure

• Remaining halves of heater strip

tested to 6kV

• Both passed, 0µA after peeling

away from where trace was

scored previously

• Remaining OD Glass removed

• Not too difficult

• Remaining heaters removed

• Not too difficult

• No More Heater Shorts, or hipot

failures possible

• Magnet probably can still be

tested…


Moving on

• Some delaminations starting at

pieces of Kapton tape can be seen

• Cable and insulation are in very

good shape going around the

ends


Other Areas of Interest

Note Crazing like

appearance in P04

(Typical)

Note fair amount of mold

release transferred to insulation

ID Generally very good except

notations below:

• Large blistering on trace LE,

appears initiated by adhesive tape

• Smaller Blisters on RE Trace,

• Small area on LE near trace

• Single (small) Pock Mark at 96mm

from LE

• Small cracks in glass similar to all

other coils

Other notations

• 2 layers of 4522 were used.

• Appearance is excellent compared

to all other tested coils I have

seen.

• Very little cracking or signs of

separation at pole or coil ends


ID appearance

• The swap did not appear to degrade mechanical

properties of this coil

• Only 1 failure was noted at ~3700V, no additional

bubbles or weak spots at the 6kV level were found

• The failure mode to the trace remains the same as in

the past.

• Using 2 layers of 4522 instead of 1 layer of 6781 greatly

improved ID appearance after testing, potentially

reducing pock marks as well.

• There is more evidence that adhesive Kapton tape

should be avoided in magnet assembly

• Heater traces and associated glass can safely be

removed after impregnation

• Comment: I believe it would be interesting to examine

the development of the blister regions to ~100+

quenches. We have a “good” coil, that should be

protectable by dump, and it could be tested.


QXFS10 General Conclusions

QXFP03:

• 1 layer JPS 26781 Glass on ID

• 1 layer JPS26781 on OD

• No copper on heaters

• R&I at FNAL

• Limiting coil in MQXFAP1b

QXFP03

• 1 layer Hexcel 4522 Glass on ID

• 2 layers Hexcel 4522 on OD

• R&I at BNL

• No limiting behavior observed in

MQXFAP1b


QXFP03 and 04 Comparison and Beginnings of Autopsy

QXFP03: The whole thing (ID) before and after

test


QXFP03 OD

18

Pre-Test appearance very

good to excellent

Some noted high

pressure areas, but

glass was otherwise

thoroughly wetted with

an excellent surface

finish

Used 3 step mold

release

Post Test appearance not as

nice

Glass was noticeably

whitened, appears to be

local debonding within

s2 glass yarns in glass

Poor sizing

performance???

A few if the large “chicken pocks”

were opened to see if anything was

inside.

• They are just a result of a void

inside the coil after testing

• We knew that

19

Examining Pock-marks on QXFP03

Notice glass appears dry

• It was not before testing

• Either result of debonding within

filaments or some other removal

of an interface

Wetting with alcohol, water, or oil did

not restore interface clarity

• Fluids were unable to penetrate

“dry” glass

• Suggests void space inside glass


More detail on glass

QXFP04 After Test

21

I don’t have pre-test images

Post Test appearance is

pretty good

Some small pock

marks, but nothing

leading to larger

issues.

Heaters look nice as

they were not fired on

ID

Generally clean coil

parts.

Side by side

22

General observations

Pre-test appearance does not have major

impact on post test appearance

4522 Glass appears to lead to better looking

coils after testing

Better looking coils appear to exhibit better

performance

Nothing noticeably unusual exists under coil ID

pock marks

23

Collecting more data for hipot-post test

comparison

QXFP04 was tested to ~4 “1st failures” per

heater trace

1st failure locations were determined

acoustically, or through other methods if

necessary

Locations were opened and examined

Sections of trace that passed were tested again

24

When a breakdown occurs, there is often an audible snap

• We use the hipotter output to activate trigger and capture audio data via Picoscope

• Run Cross-correlation between signal window to find time delay of arrival (TDOA)

• Using constraints of system calculate location

• Accurate to <1cm when it was quiet in the shop without advanced calibration


Adventures in Acoustics: Hi-Pot Failure Location


Finding weaknesses: More of the same

Some poorly adhered Polyimide and a line

across the coil


• A similar pattern in hipot

failure voltage was noted in

QXFP04 as in QXFP01, though

the slope is slightly steeper

• This test was not exhaustive in

QXFP04 as in 1b, though it

went to a higher voltage

• Heaters 1 and 4 (midplane

heaters) did well again

• Pole heaters performed rather

poorly

28

1st Failures: QXFP04 and QXFP01


Bubble plots compared

Notes here: Color indicates hipot breakdown

voltage. Green is passed at test condition, red

is lower breakdown voltage, black is ~6kV Test

voltage.

Bubble size indicates relative size of bubbles in

heater

Revised Bubble

Color Key

Passes Hipot

1500V Hipot Failure

3750V Hipot Failure

6000V Hipot Failure

HT1 T MP

HT2 T Pole

HT3 NT Pole

HT4 NT MP

• Things to note from both charts are:

• There is an asymmetry the NT side has

substantially more spots than the T side

• All coils (including some of the others we did

some of this study on not shown) have a

problem area at ~2160mm from LE, which has a

visible line across it likely from a weld.

• The Pole has substantially more hipot failures

and visible blistering than the midplanes.

• Lack of bubbles on QXFS10 could be from:

• The Swap

• Low number of quenches

• Improved production processes.• I would guess it's one or both of the last two


Comments on above

• When allowed, QXFP03 will

undergo hipot and heater

removal

• Samples have been

harvested for tg testing form

P04 and are ready to ship

• ~2 days left on P03

• Coils will be sectioned for

additional analysis and glass

sample preparation


Ongoing work

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Continued Coil Autopsies - CERN