1. 1 Stony Brook Update T.K. Hemmick for the Tent Crew

2. 2 HBD has returned to Stony Brook Detector arrived, but trouble with gas cart: –New magnahelic was leaking. O 2 under 1 ppm when pressure > 1” water. O 2 over 100 ppm when pressure < 0.5” water. Replaced. –Water sensor went bad. H 2 O read 60 ppm from bottle. Bob replaced electronics card…5 ppm from bottle. Placed in glovebox, water dropping SLOWLY –Recirculation started Friday 1:30 AM –Monday 5 PM water @ 16 ppm. –Electronics (rohacell?) ourgassing heavily. –Probably will need to regen scrubbers soon.

3. 3 Visual Survey

4. 4 Every Imagined Feature “Dust” –Better described as shavings. –Delrin or G10 “patches” around the posts. –Likely unavoidable, but does not make sparks. “Scratches” –Four cross-piece scratches on each GEM. –These are not the non-linear current points. “Pock Marks” –Four patches (one per quadrant). –These match locations of GEM-mesh sparks. –These DO draw the non-linear currents.

5. 5 Try to get closer pictures Theodolite provides telescopic function. Cell phone takes pictures through theodolite. Need better solution …

6. 6 Pock Marks Human eye could see the holes. Holes smaller than pock parks. Pocks almost certainly from mesh  GEM

7. 7 Scratches?? Look similar to pocks. So far, not the source of trouble

8. 8 Spotting a non-linear Current Draw… HV measure on strip is a voltage divider Meter impedance is always same, but each GEM resistor differs. However, if one measures TWO input voltages (400V, 100V), the ratio of the output readings is the same for all R G unless there is a non-linear current draw. Non-linear current sensor:

9. 9 Non-linearity Measure vs Strip number The non-linearity measure eliminates scattrer due to un- equal GEM resistors. Shows directly which strips are drawing the non-linear current. MOSTLY aligned with the Pock Marks (a few might be aligned with the “scratches”). Aligned with Pock Marks

10. 10 Aligned with scratch??

11. 11 Continuing work. Complete non-linearity map. Get MUCH closer pictures –Purchase something? –Telescope + CCD? –Microscope on removed GEM? Want to complete all things that can be done in N2 before closing walls. –Spark-induced feedback in N 2 –How man strips fire per spark. –What is up with the QE measurement??

12. 12 Executive Summary Pock marks are large features (bigger than holes) that are clustered around the places where GEM  mesh sparks occur. Pock marks are the principal source of the non-linear current draw. “Scratch” marks might be scratches but might also be GEM  mesh sparks. Some “Scratch” marks show non-linearity. Likely scenario is that GEM  mesh created the Pock Marks.

13. 13 Ironies GEM sparks are known to do damage VERY infrequently. GEM  mesh sparks are apparently much worse. Our conservative trips settings exacerbated the damage, rather than protected HBD. Our HV capacitor on the grid exacerbated the damage, but likely does no filtering. Once Bob reported GEM  mesh troubles. TKH and others discounted this with language like “In my experience this does not happen.” –This simply proves insufficient experience.