During, the week of February 14, both Vincent
and I worked on getting the Mini-TPC ready for RHIC beam. As of
today, the accelerator plans to close up on March 15 and start
accelerating beam on April 1. We might expect the first real beam in
May.
During the last run, we had approximately one
sector working. When I tried to start looking at the remaining
problems, I turned off the Fastbus power. Then a digitizer died. Dave
sent back the digitizers to France.
When we started we first tried to resurrect the
Fastbus system. After a struggle, we were only able to get three out
of four digitizers working. Also, we found one pre-amp shaper had
blown a fuse. When we replaced the fuse, the fuse immediately blew.
To maximize the number of channels, we aligned the bad pre-amp shaper
with the bad digitizer. (The digitizer does function as a Fastbus
module, but does not produce any data).
We also struggled with the initial amplifiers.
We found that two cables were plugged into the ground plane. This
reduced the current from the 5 V power supply. This also, I believe,
introduced the 30 kHz noise into the system. We found one bad
amplifier channel and aligned it with the bad digitizer channel. I
added some inductance to t the power supply leads from the Assembly
Hall. These devices reduced the background noise count by a factor of
two.
We had some trouble with the gas system.
Apparently, one gas line was broken during the last few months. We
(with the help of Alexi) fixed the line after wasting some
gas.
In the process of upgrading the analysis
computer, I managed to break it. The connector for the video board of
the Vax 4000/60 was badly damaged during shipment to BNL. The
connector was falling off. During the addition of the new upgraded
parts, I managed to hit the connector one too many times.
BNL just repaired the computer and it is now
online. I upgraded the memory to 108 Mb and added a 2.5 Gb disk. The
next time that I get back, I will install a tape drive so that we can
make backups.
A number of superfluous LAL equipment has just
been sent back. Included in this package is a broken digitizer and
shaper module.
As a result of these changes, we have 4 1/2
sectors out of 6 working. This is clearly enough to do beam studies.
To test the chamber we pulsed it with the gated grid. This is shown
here. Note, that the first few channels are noisy and only some are
working. This problem is either in the digitizers or the shapers. We
did not further trouble shoot the problem.
We checked the performance of the chamber by
pulsing the gated grid. We integrated over about 20 events
and
plotted the time versus pad position
for each channel. Note, that the first 48 channels are missing from
this plot. From this data, we can plot an amplitude
spectrum. Upon placing an amplitude cut on the data, we can see a
much cleaner
spectrum. Using an amplitude cut, we
can also look at the
variation of time for each pad. Notice,
the time is very uniform.
After these data were taken, we placed filters
on the lines. The filters cut down the number of hits in the chamber
by a factor of two. We then triggered the chamber with high voltage
on and the gated grid before the trigger. There should be only noise
in the following plots which had about 50 events of data. First, we
look at the position
versus time plot. Note, there are a few
noisy pads. If you look the
amplitude spectrum, you can see that
the data is clustered at low noise. The time
spectrum is flat in time as
expected.
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Using the digital scope, I was able to
trigger on Cosmic Rays. The mini-TPC is vertical, so that
each group of 16 amplifiers is also vertical. There are two
pictures of the triggers. Each
picture shows the vertical
traces from four wires. Depending on the geometry, different
wires fired. As you can see the signal for a cosmic ray is
significantly higher than the noise. Each trigger showed a
hit on at least one other wire. Most of the time there were
four hits. I was only able to save two of the pictures, as
the scope's disk drive was not very reliable.
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Vincent and I had lunch with Angelica. Angelica
mentioned that RHIC is becoming more interested with measuring the
direction of the background. We decided that we should make a
demonstration on the capability of the detector before further
action. While it is true that the effectiveness was demonstrated at
SLAC, we felt that with the present manpower, it was important to
demonstrate a proof of principle.
During the debugging, we received excellent
assistance from Ralph, Tony, Hank and Tim.
The next expedition for the mini-TPC will be
when there is sufficient beam to do a measurement.
