Method
A first attempt to measure the gain as function of the wire offset to the middle of the straw was performed with this setup:

The straw is aluminised  of 7.5 cm length and an inner  diameter of 5 mm and is placed in a closed box, with the gas flow approximately along the straw. The wire has a diameter of 0.025 mm . The position of the straw is measured both with a micrometer and a clock. The later being more precise, only its values are recorded in the data files. The middle coordinate (as given by the clock) is  3.453 mm. 

Two  Sr90 sources,  of 2  and respectively 20 mCu were used. 

The schematics for the current measurement is the following:

to come ... to check  the distance from the source to the straw...
Data files : units, sample analysis programs 

If not specified otherwise,  the units in the data files are the following:
  • temperature: degrees Celsius;
  • pressure: mbars;
  • current: volts;
  • resistance: ohms;
  • radioactive source activity: mCu;
  • gas flow: l/h.
A sample analysis program (C++),  saba  is available as executable. It reads the data files and creates kumacs that should be run under paw to obtain ps files. Since the program source is also available, modifications should be straightforward.

to come ... the source is not yet available after the latest modifications ....
Variation of the gain with ambient pressure and temperature
For a wire position of 3.5mm (measured with the micrometer, approximately in the middle of the straw) , several measurement sets were taken in order to find the gain variation with the temperature and with the pressure. In a first approximation, this variation was parameterized as:

I=I0*exp(a*V-bT/p),

with T expressed in Kelvin, p in mbars and V in volts.

Datafiles  prema0407_1600, prema0607_1600, prema0807_1600, prema0907_1600 contain  measurement sets of 50 points each, taken over several days, in different temperature and  pressure conditions, but at fixed voltage on the straw (~1600V).  The pressure in the data files is the atmospheric pressure, as read with the liquid barometer. The overpressure in the straw box is approximately 6 mm of oil (0.6 mb). The temperature was read with the Hg thermometer, placed on the straw box. 

The measurements were performed with the PREMA meter (300 mV scale, 2 s integration time). From the spread of the current measurement  within  each set (see prema0*07_1600.ps files), an error of ~0.3 mV is estimated on the mean current  measured in the set.

To facilitate the fitting, the results were gathered in prema_1600, with the entries after the tag  current being the mean current measured and its estimated error. The results were:
I0exp(aV) = 464.951 mV                 b=28.74 mb/deg

to come ... the previous fits were done with T in C instead of K, and the overpressure in the box was not measured.
to come .. discussion of the new files (prema0808_pres)
Variation of the gain with the wire position
Measurements before 03/08/2001
For this set of measurements, the pressure in the files is the atmospheric pressure and the overpressure in the straw box is approximatively 6 mm oil (0.6 mb).

The curve I=I(x) was measured with two different sources (2 and 20 mCu) and at different voltages:

This measurement was performed with the 20mCu source, but at a height of 8.5 cm from the box: data (plots).

To check the gas flow importance for the stability of the system,  the curve was measured also immediately after the gas flow was stopped - data (plots) - and repeated - data (plots).
Measurements after 03/08/2001
The pressure and temperature  are measured  with the AE sensors. The pressure is measured in the middle of the box and the temperature near the straw box.

to come .. discussion of the new files

Cristina Cârloganu
Created: Tue Sep 18 13:32:09 MET DST 2001
Last modified: Tue Sep 18 16:42:09 MET DST 2001