Hi All;

  I put together a slide showing typical gain curves for one of the GMT chambers with both 10% CO2 (C10) and 30% CO2 (C30) mixes (attached .pdf).  The chamber is illuminated with a 55Fe source and we derive a trigger from the bottom of the bottom GEM (facing the readout plane called “last foil” or LF).  Two signals are plotted in the attached graph – the last foil signal and one of the readout plane signals (AMP2).  We group readout channels into 4 groups for each coordinate so the signal AMP2 represents ¼ of the chamber readout board.

 The plots show that for equal gain you need ~450V higher voltage for C30 vs. C10, and for the same voltage the C10 gain is about 10x higher than the C30 gain.

 “Gain” here is the adc channel of the 55Fe main peak (Gaussian fit to the central part of the peak).  The inset in the upper right of the page gives the numbers for the data points if anyone wants to play with them

 Best regards,

 Dick Majka