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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
S. Krave | QXFS10 Autopsy 6
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…
S. Krave | QXFS10 Autopsy 7
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
S. Krave | QXFS10 Autopsy 8
Removing short (as before)
Detail of the Hipot Failure Location
S. Krave | QXFS10 Autopsy9
This looks familiar…
S. Krave | QXFS10 Autopsy 10
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
S. Krave | QXFS10 Autopsy 11
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…
S. Krave | QXFS10 Autopsy 12
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
S. Krave | QXFS10 Autopsy 13
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
S. Krave | QXFS10 Autopsy 14
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.
S. Krave | QXFS10 Autopsy 15
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
S. Krave | QXFS10 Autopsy 16
QXFP03 and 04 Comparison and Beginnings of Autopsy
QXFP03: The whole thing (ID) before and after
test
17S. Krave | QXFS10 Autopsy
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
S. Krave | QXFS10 Autopsy 20
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
S. Krave | QXFS10 Autopsy 25
Adventures in Acoustics: Hi-Pot Failure Location
S. Krave | QXFS10 Autopsy 26
Finding weaknesses: More of the same
Some poorly adhered Polyimide and a line
across the coil
27S. Krave | QXFS10 Autopsy
• 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
29S. Krave | QXFS10 Autopsy
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
S. Krave | QXFS10 Autopsy 30
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
S. Krave | QXFS10 Autopsy 31
Ongoing work