Large Cell Scope Pictures, Part II
This is a follow-up on Richard’s measurement of large cell signals.
In addition to his test I added a small, 7 cm z-strip under the LST.
This z-strip is made out of copper tape, about 7x15 cm^2. It is connected
via a BNC connector and a 50 Ohm coax cable to a scope (50 Ohm termination)
If have updated the two drawings below taken from Richard’s presentation.
Ground plane above cathode and below tube (see picture below)
Please note that there is an asymmetry in the chamber endcap: the HV pins are not
located at the symmetry line but closer the the bottom of the tube. According to the
drawings of the large cell tubes that are available on the web, this is the closed side of
the profile. If this is correct, our phi signals come from the open side of the profile, the z
signals come from the closed side.
phi strip
g
++0++
g
g=gas fitting
+=HV
0=ground
z strip
S1
Phi Cathode signal
Gnd
1nF
HV
Z cathode
signal
Large Cell Tube
S2
S1
S2
Anode signal
scope
Example 1: Anode at 20 mV, z at 10 mV and phi at 5 mV per division
Example 2: Anode at 20 mV, z at 10 mV and phi at 5 mV per division
Example 3: Anode at 20 mV, z at 10 mV and phi at 5 mV per division
Conclusion:
• We see signal in coincidence at both cathodes and the anode
• Anode signals are the largest.
• Followed by the z strip signals (which we believe come from the closed
side of the profile) which are about ½ the size of the anode signals.
• The phi signals (which we believe come from the open side of the profile)
are about ¼ the size of the anode signals.
• Clearly this is not a complete test. The next step is to measure pulse
height spectra for each signal source, check the HV dependency etc.