Voltage curves
shows the efficiency, current,
and singles rates for these two counters prior to any water tests.
I built two 63.5cm x 63.5cm RPCs. One called (RPC 1) was used as a control. The second (RPC 2) was set up so that we could open valves to bubble the inlet RPC gas through distilled water. We could then close these valves and flow RPC gas directly into the RPC to dry it out.
Voltage curves
shows the efficiency, current,
and singles rates for these two counters prior to any water tests.
Water tests
shows the efficiency,
current, and singles rates for both counters as a function of time.
We were flowing about one volume change per hour into each RPC.
The voltage was left at 8kV for the duration of the test.
On four separate occasions we introduced water into the RPC. The current began rising immediately. After about 2 volume changes the test RPC was essentially dead - no singles rate or efficiency. The current went as high as 19 microAmps/m**2. We then began flowing dry RPC gas and within a couple of volume changes the efficiency was back to 90+%. The current and singles rate were higher than before the water tests but are continuing to improve.
This indicates that, at least for short durations, water does not permanently disable an RPC. We will continue to monitor this RPC and then try a longer duration test.
On December 8, 1998 I inserted 12m of polyolefin into the inlet line of the test RPC. The tubing was brought from KEK and was the same as was used in the initial Barrel KLM installation. I placed the tubing in a glass box with distilled water in the bottom. The relative humidity in the box was 98% at 23.4 degrees C. I ran the test RPC at operating voltage (8.0kV) flowing approximately 4 volume changes per day. After eight days with no change I warmed the box and had a relative humidity of 75% at 32 degrees C around the tubing for the remainder of the test. Below I show the efficiency, current, and singles rate for the test RPC and the reference RPC as a function of day of operation. On day 63 I removed the polyolefin tubing on the inlet and began trying to dry out the RPC. Testing continues...
water test
Send Suggestions to morgan@amy.phys.vt.edu.