Minutes of the ST-Testbeam Run-Meeting - July 10, 2004
=====================================================

General
-------

Since the last 4 shifts, we have had very
stable beam, and in fact we have finished
the pulse shape scan.


Actions since yesterday
-----------------------

- the pulse shape scan has been finished, and therefore
  the night-shift crew replaced the Irrad-1 sensor with the
  Irrad-2 (30 years) ladder.

- a high-voltage scan was started

- the day-shift crew decided to find the optimal
  HV setting for the Irrad-2 sensor.

  In a first effort, the following results were found:

      HV:   200V | 250  | 350  | 550  | 600  | 600*
      -----------------------------------------------
      T_s: 23.1  | 24.0 | 26.0 | 31.2 | 33.1 | 36.4
      T_h: 22.3  | 22.4 | 22.7 | 23.8 | 24.3 | --
       I :  3.1  | 3.8  | 5.3  |  9.1 | 10.6 | 13.7

* note that it takes quite some time for the current to stabalize,
  the second reading at HV = 600 was taken approximately 15 minutes
  afte the first one.


Unfortunately, only very little signal was found in the
data, even at 600V only a S/N of maybe 4 was found.

In a second effort, it was noticed that at the same
HV, a lot more current was drawn, and of course, a higher
temperature was measured.

Then, suddenly the current dropped to zero, and it
was clear something was broken...

The shutter was moved in, to gain access to the area,
and the Irrad-2 ladder was removed. A clear smell of
something burning was observed. After inspecting the
ladder, it was noticed that a resistor looked rather
burned, and is most likely broken.

The Irrad-1 has now been put back in the box,
and surprisingly enough, the smell was still there.

It was then noted that on this ladder, the same resistor
looked rather burned as well. In fact, some plastic has
even melted away.

Therefore, it is no more surprising that that resistor
on the Irrad-2 sensor has burned out...


To be specific: this is one of four resistor used
in the circutry which feeds the HV to the sensor.

Task List
---------

Since the Irrad-2 had to be replaced, the program
has changed as well.

After inspecting the HV scan, it was decided to
fill in missing points in the HV scan.
Note that the HV points with values higher than 400V
will be measured last...

A list of missing points has been noted down in the
logbook.





Cheers,



	Johan Blouw