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EN4 Single GEM Tests

B.Azmoun, M.Proissl BNL, SUNY SB. EN4 Single GEM Tests. EN4-Top. Chain R ~84M-0.8M=83.2M.

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EN4 Single GEM Tests

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  1. B.Azmoun, M.Proissl BNL, SUNY SB EN4 Single GEM Tests

  2. EN4-Top Chain R ~84M-0.8M=83.2M • It is not clear (at least to me) that knowing the correspondence between dV and the parallel resistance (as determined form the single GEM tests) will allow a straight forward determination of the behavior of the short resistance when placed in the voltage divider…as Craig W. has mentioned, we need the dV to determine the resistance, but need the resistance to determine the dV. • To illustrate the point, according to the plot above, the parallel resistance near a dV of 500V is ~9.2M. If this R|| value is inserted into the divider chain (in place of the nominal 10M), the chain current may be computed as 500V/9.2~54uA, corresponding to a Vin of 54uA*(74M+9.2M)=4522V. However, since this same Vin is also applied to the other two GEM div. chains, it is unclear (in a trivial way) what the resulting dV or resistance across the other GEMs would be.

  3. EN4-Mid. Chain R~84M-2.5M = 81.5M

  4. EN4-Bot. Chain R = 84M-4M =80M

  5. LeCroy Vin Vs. MC (Good Vs. Bad GEM Mod.) • By looking at the LeCroy MC, we can gain some handle of the true behavior of the GEM shorts as they operate within the div. chain. • Using the diminished Div. chain Resistor values from the Bertan tests (at high dV) of 83.2M, 81.5M, and 80M for EN4-T,M,B respectively, the R|| for the three chains would be 27.2, very similar to what we see for the LeCroy derived R|| at high voltages. • If the difference between the actual LeCRoy Measured Current and the current expected from a healthy GEM is attributed to the bottom GEM alone, the dV across the GEMs would be as depicted in the plot to the right.

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