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Stony Brook Update

An update on Stony Brook's detector system: gas cart troubles, leaks in magnahelic and O2 levels fluctuation. Visual survey reveals potential sparks. Non-linear current draw investigation suggests connection to pock marks. Suggestions for further testing and equipment purchases discussed.

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Stony Brook Update

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

  2. HBD has returned to Stony Brook • Detector arrived, but trouble with gas cart: • New magnahelic was leaking. • O2 under 1 ppm when pressure > 1” water. • O2 over 100 ppm when pressure < 0.5” water. • Replaced. • Water sensor went bad. • H2O 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. Visual Survey

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

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

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

  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 RGunless there is a non-linear current draw. • Non-linear current sensor:

  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. Aligned with scratch??

  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 N2 • How man strips fire per spark. • What is up with the QE measurement??

  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. 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.

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