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.

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.

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.