Mini-BooNE Collaboration Meeting
University of Cincinnati
September 14-15, 2000




Outline

1.    Number of tubes tested, and their location
2.    The new VXI system from Los Alamos
3.    Comparison of data acquisition between the "old" and "new" system
4.    Data analysis
  • Q, T distributions
  • Gain, Dark Noise Rate
  • Gain vs. Voltage
    • 5.    Summary and projected testing schedule



     

    Presentation given by Darrel Smith

    Figure 1 shows where the photomultiplier tubes (PMTs) are located at Fermilab.  We are testing two models of PMTs, the "old" LSND tubes and the "new" Hamamatsu tubes (both models are made by Hamamatsu).  PMT testing started in May with fifteen 55-gallon barrel drums.  In July, it was moved to the New Muon Lab where a dark room was constructed to hold up to 46 tubes (30 LSND and 16 new Hamamatsu tubes).  At the time of this meeting, 799 of the 1550 tubes were tested.

    Figure 2 shows two pictures of the data acquisition electronics.  The first picture shows the "old" setup used in July and August.  The maximum number of tubes that could be tested in a 12-hour period was 24.  This was a very labor-intensive project where the dark currents were measured by hand and 600 waveforms were collected for each tube at a rate of 25 min/tube (LSND) and 35 min/tube (new Hamamatsu).

    The second part of firgure two shows the new VXI crate with 22 cables connected between the VXI crate and the pick-off box of the old data acquisition system.  The VXI crate can acquire 10,000 waveforms in ~90 seconds.  Furthermore, it can automatically and independently change the voltages on the LeCroy power supply for each tube.  Each tube can have its dark noise rate measured automatically, because the pulser is completely under control  within the VXI crate.  Furthermore, the waveforms are collected so rapidly that we now store 1000 waveforms for each phototube.  We had to shut down the tube testing from September 1-8 so we could install the new VXI system.  A "special thanks" to Shawn McKenney (ERAU student) for putting in a herculean effort at Los Alamos and Fermilab to get this system up and running.  Also, "thanks" to Vern Sandberg for overseeing Shawn's work at Los Alamos, and assisting us over the phone from Los Alamos.  The new system is up and running and we are able to test 46 tubes in 2.5 hours.  This will completely change how we go about our daily schedule for tube testing.  Furthermore, it will permit us to finish testing by our planned due date, November 1.

    Figure 3 shows some early problems with the waveforms coming through the new VXI system.  This problem was fixed (Figure 4) by reducing the other tube voltages to 1,000 volts when testing each tube.  Since then, the problem was traced to poorly made high-voltage connectors.  The high voltage connectors are being checked with every "change out" and any problems are immediately fixed before the tubes dark adapt overnight.

    Figure 5 shows a comparison between a couple of waveforms measured on the old GPIB versus the new VXI data acquisition system.  These waveforms were taken from the same tube to look for striking differences in the old and new data acquisition system.  The pulses have the same qualitative appearance using the new VXI system.  The "new" pulses have a slightly noisier pedestal.  This problem appears to be due to the quality control of our "cheap solution" for HV connectors.  We're using automobile connectors because they're easy to connect and require a lot less labor.  We'll keep an eye on the pedestals to make sure they don't get abnormally large.  The pedestal is correctly set at ~75 counts and waveforms appear to be in a time range of 100ns.  There was concern that the pulse widths may have changed between the two systems, but this doesn't seem to be the case.  Another test was proposed to clarify the concerns with the timing and amplitude scales and this is shown in figure 6.

    Figure 6 demonstrates a more critical test of of timing and amplitude by injecting a known "negative" pulse with a width of 20ns and an amplitude of 11-13 mV.  This test was performed with a frequency generator and an attenuator box.  The pulse had a frequency of 1kHz and the resulting waveform was read out using the same procedure that resulted in the previous figures.  The output waveforms are in very good agreement with the calibrated input.  We are now confident that the time and amplitude scales are correctly set in the software.

    Figure 7 shows the PMTS testing schedule for the next six weeks.  It appears that with the new VXI system, we now have the capacity to test all the tubes by November 1.

    Presentation given by Bonnie T. Fleming


    A preliminary plan to group PMT's to determine their location in the tank was presented.  PMT's will be grouped into the veto or the main tank.  Veto tubes are then subdivided into the ones we use and the ones we don't need.  Main tank PMT's are subdivided into groups A, B, and C, each group being equally distributed in the tank.  Operating voltages will be determined at a chosen gain and the tube will then be grouped based on how it passes certain cuts at that voltage.  PMT properties to be cut on include dark rate, pre and post pulsing rate, timing resolution and charge resolution.  We are still considering other properties such as charge tails.  Presented are these PMT properties for all the tubes tested so far for average gain.  There is still work to do to understand testing data and analysis code.

    Figure 1 shows gains in four voltage groups for the new Hamamatsu PMTs in red, and in two voltage groups for the LSND tubes in blue.  From the left the voltages corresponding to each red histogram are: V(a)=Suggested Operaitng Voltage -100V, V(b)=Suggested Operating Voltage, V(c)=Suggested Operating Voltage +100V, V(d)=Suggested Operating Voltage+150V.   From the left, voltages corresponding to each blue histogram are: V(a)=Suggested Operating Voltage -50V, V(b)=Suggested Operating Voltage+50V.  Main overlap region of both sets includes V(c) and V(d) groups for new Hamamatsu tubes and V(a) and V(b) for LSND tubes.  These voltage groups are plotted in Figure 2.  PMT properties shown after this are for these groups only.

    Figure 3 shows darkrates at the suggested operating voltage for each tube.  LSND PMT's tend to be quieter than the new ones which is probably because they have been conditioning in the LSND tank for six years (!).  PMT's below 8kHz should be fine.  PMTs above this need to be looked at.  They are either bad tubes, have been tested when we had light leaks in the testing room, or are a consequence of a problem in the analysis code.  These are being looked into.

    Figure 4 shows the fraction of late pulsing seen for LSND and New Hamamatsu PMT's.  Again the LSND tubes are quieter probably as a result of the extra conditioning time.  Hamamatsu specs indicated an expected 3% or lower late pulsing rate.  We see some new PMT's with higher rates than this which need to be looked at in more detail.  There is a known bug in the analysis code which can call normal pulses occuring later in the scope trace as double pulses.  This may account for some of these outliers.  It is being fixed.

    Figure 5 shows timing resolution for the PMT's.  The new Hamamatsu PMTs have much better timing than the LSND PMT's.  The spread in the LSND timing distribution may be due to the measurement process instead of actual differences in the PMT's.  We will use our calibration PMTs -- the permanent tube and the rover tube --  to determine this.

    Figure 6 shows the charge resolution.  Again it is clear that the new PMT's are substantially better that the LSND PMT's.  There is a spread in the LSND PMT's which can be used to subdivide these PMT's.

    Figure 7 shows Log gain versus Log voltage for three new Hamamatsu PMTs (with four points) and two LSND PMT's (with two points).  As expected, the points are a straight line on log-log plot.  We will fit the points to a line to determine voltage at any gain for each PMT.