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Helsinki T2 status

Helsinki T2 status. Risto Orava/ on behalf of Kari Kurvinen 8.11.2005. the 1 st production GEM under tests (operational tests)

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Helsinki T2 status

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  1. Helsinki T2 status Risto Orava/ on behalf of Kari Kurvinen 8.11.2005 • the 1st production GEM under tests (operational tests) • the 2nd GEM not accepted due to persistent leakage current problems in two foils (all other parts finished) - wait for components for replacement (and for further GEMs) • spare parts needed in future to avoid delays in the future

  2. Characterisation of GEM foils: • leakage current measurements • visual inspection • optical scanning

  3. Leakage current measurements of GEM foils • the four segments (A,B,C & D, see Fig.) of the GEM foils are measured separately by Picoamp /Voltage source device (Keithley 487). • leakage currents are measured three times during the assembly (the foil before and after framing, then after gluing into a stack). 3 x 3 foils x 4 36 measurements / detector • current limited by 100 MW resistor (corresponding to the max current of 5 mA at 500V). • a foil is approved if the current stays at < 0.5 nA for 5+ min @500V • so far 2 /12 foils found to be bad. These were observed to be temporarily short circuited during the second measurement! Both exhibited instabilities during the first measurement, still passed the criteria. • due to these observations, a graphical display (Labview) was added to the measurement system to detect & document instabilities as early as possible (the display was not yet available for the first production GEM).

  4. noise 0.5 nA A bad GEM foil A-segment is short circuited (60 – 150 kW) B-segment 0 min 10 min TIF HV ramp up B,C & D segments OK 0.5 nA (Note: the time scale in the plots must be multiplied by two) noise C-segment 6 min 0.5 nA noise D-segment 6 min

  5. A ”good” GEM foil ? HV ramp up spark! N2 flush started > 10 min in air 0.5 nA N2 flush stopped 0.5 nA A-segment A-segment 14 min 20 min spark! in N2 in N2 > 5 min C-segment 12 min B-segment 14 min in N2 (Note: the time scale in the plots must be multiplied by 2) noise D-segment 10 min

  6. Visual inspection defect in the mask  0.5 mm • only the largest visible defects are observable • coordinates are recorded approximately • serious defects due to dust, stains or scratches are • easy to see number of recorded defects in the six latest foils: GEM 1 18, 12, 10 (top, middle, bottom) GEM 2 10, 31, 40 defect in the mask General observation: the quality of GEM foils is good (i.e. is significantly improved from the past)

  7. Optical scanning of GEM foils • scanning in mixed mode (transparent + • reflective) • blue diffuser produces a colour • contrast between the holes and copper • surfaces 1.8 million GEM holes scanned pictures can be analysed by using fitting algorithms to count anomalies and to register their coordinates AIM: a quantitative measure of the quality of GEM foils defects, dust, scratches,etc The worst foil so far: Blue curve shows all the seen objects; the red one only the ”roughly round ones” (e.g.scratches are filtered out). The number of defects (red ones > 80) was 240, while only 40 were found under visual inspection (see previous slide).

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