June L. Rossi et al. Further analysis of union 2, heater )Measurement of R GND of the short. 2)Observation at electron microscope and XPS chemical analysis (only general information given here, more details will follow) 3)Thermoimages of the short under current 4)Detailed x-ray of the region of the short 5)Next Steps by A. Chincarini, G. Gariano, L. Rossi, A. Rovani and E. Ruscino - INFN Genoa Done on the half-connector after the metallographic cut prepared at CERN by Gerardin and Sgobba.

June L. Rossi et al. Resistance = 38 m  (4-point measurement) (it was 23 m  before machining out half of the connector)

June L. Rossi et al. XPS chemical analysis on the crack confirms SEM: only C and O (i.e. epoxi) and traces of Al 2 O 3 The same analysis outside the crack (on glue) give the same results with increased Al 2 O 3 (also visible as grains) it is apparent that the glue in the crack boiled (melting point 311 C), therefore gas has been produced. bubbles Note: dimensions on pictures wrong (50% of real), white arrows are correct 2mm 0.8mm 0.27mm Stycast MgO

June L. Rossi et al. Bubbles and grains in some more detail. R between any 2 points 1mm apart on the surface of the melted epoxi >M  Bubbles Al 2 O 3

June L. Rossi et al. Injected a known current through the 2 shorted (38 m  ) electrodes and measured with high-resolution thermocamera 1A

June L. Rossi et al. 2A Each thermopicture taken a couple of seconds after change of current

June L. Rossi et al. 4A The hot spot is in the “void” at the end of the Stainless Steel jacket 0.6 Watts

June L. Rossi et al. 7A 2 Watts

June L. Rossi et al. 7A If we instead wait for some 20 sec, T max does not change but heat spreads

June L. Rossi et al. 9A Note: the fuse was a 12A one and the current was likely 20A, so it was pretty hot downthere at the time of the fault… 3 Watts 2mm

June L. Rossi et al. At 10 A we damaged the contact joints to drive the current on top of the electrodes, so we stopped. The resistance remains unchanged (35 m  ), but the melted region now appears different (free surface)

June L. Rossi et al. Tried to look inside the “hole” with Auger electrons, but failed, need the sample to be cut perpendicular to the wire to directly access the faulty region. This is also necessary for a more detailed SEM analysis. To prepare for this we x-rayed the sample under different orientations (see next pages). T increaseses ~linearly with power, if the extrapolation holds up to 15W, then T~1500 C!

June L. Rossi et al. Rotation around the wire by an angle  Face-up,  =0 0  =30 0  =60 0  =90 0 Hot spot This side higher

June L. Rossi et al. Almost face down   =170 0  =150 0  =120 0 X-rays indicates that: –there are high-Z fragments in the region of the short (underneath the hole) and some inside the melted epoxi. –The stainless steel jacket is damaged –The defect is local and (luckily!) opposite to the machined surface

June L. Rossi et al. 84 keV  = keV  = keV  = Same image at different x-ray energies

June L. Rossi et al. Perspective view. The “stone” is just under the wire and on the side where the “hole” is. High-Z fragments

June L. Rossi et al. What did we learn through the measurments reported here: –Epoxi melted and produced gas (T>311C) during the fault –T may have gone very high with available I and Power –The hot point is inside a cavity (T max = P max = cavity and fracture) –There are high-Z fragments at hot point and dispersed in melted glue –The SS jacket around the hot point is missing/damaged What do we need to still find: –How R GND went from >2 G  to fraction of a 

June L. Rossi et al. To proceed we must: –prepare a metallurgical sample with a surface perpendicular to the wire and machined down to the place where the “stone” is. –Make SEM analysis of this sample (this should tell us what are the chemical elements in the “stone” and surroundings) –If necessary, make XPS and Auger analysis of the sample (this may tell us which is the molecular composition of the “stone” and surroundings).