In 2009 run STAR collected data while changin voltages in the TPC wire chambers to see the effect on the gain.

The data files analysed in this study are :

http://www.star.bnl.gov/~iraklic/iTPC/VoltageScan/daqFileList.list

The voltages ruging runs are (inner/outer):

http://www.star.bnl.gov/~iraklic/iTPC/VoltageScan/voltages.txt

The number distribution of the numbe rof pixels in different runs are shown below:

This clearly shows two bumps at high voltages, which desappear with lowering the voltage.