Hello Everyone,
The main goal of tonight was to look for an increase in chamber noise over
the course of a shift due to space charge effects .The gas mixture was
Helium-Isobutane 70:30 and a sense wire voltage of 3900 was used since it was
found to give reasonably flat tdc distributions. Summaries of the runs are
as follows:
Run | Torroid | Sense Wire Voltage | Threshold
Voltage (V)
----------------------------------------------------------------------------------------------------
1933 OFF
3900 2
1934 OFF
3900 2
1935 OFF
3900 2 except boxes L0,2,4,6 set to 3 V
1936 OFF
3900 2 except boxes L0,2,4,6 set to 3V
1937 OFF
3900 2 except boxes L0,2,4,6 set to 4V
1939 ON
3900 2
1940 ON
3900 2
1941 ON
3900 2
1942 ON
3900 2
1943 ON
3900 2
1944 ON
3900 2
Several interesting points to note
1.) S/B for were high with the field on and showed no significant decrease
with time. That is, we had
Chamber S/B
0 ~ 4:1
1 ~ 5:1
2 ~6:1
for runs 1933 and 1937.
2.) Boxes L0,L2,L4,L6 which had the resistors to ground removed had smaller
signal to background ratios as compared to the equivalent boxes in the right
sector. Increasing the thresholds appeared to just reduce the overall rate
with S/B remaining the same.
3.) In runs with the field off, the background increased significantly.For
example, in Chamber 2 Right Sector:
S/B ~6:1 Field On (Run 1936)
S/B <2:1 Field Off (Run 1940)
4.) Also towards the end of the night there may have been a slight increase
in noise. The effect may have been accelerated at the end of our shift since
with the field off the rates were much higher by about a factor of 2.
5.) 1/16 " Lead Foil produced a noticeable reduction in background as seen in
the tdc distribution.
Abigail Goodhue and Adam DeGrush
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:28 EST