Measurement of big pulses in straws in the openable chamber
The openable chamber is a special chamber in which straws can be exchanged for studying their behaviour.
Especially the behaviour of straws as a function of the type of wirelocators has a big correlation with the presence of
big pulses. Big pulses are always present as one can see from the study of puls height spectra. The puls height
spectra show always a big tail. In the openable chamber we connect two straws at the end to get a straw that can
be read out at both ends. From the scope pictures it was already clear that some pulses are created by the wirelocators.
At the moment we have studied two types of wirelocators: a twistor made of POM  and a wirelocator existing of
two V shaped endpeaces that support the wire. The V shaped wirelocator is made of Noryl.The POM wire locators were used in the straws 1 to 6 and the double V noryl wire locators were used in the straws 35-40.

Here is a picture of a V shaped wire locator:

Noryl wire locator

Another picture of the same noryl wirelocator:

Noryl wire locator

A picture of the POM twistor:

POM twistor
 

The gas mixture is Ar/CO2 65/35 % and the HV is 1700V. The electronic configuration of the measurement presented at 19-2-2002 is the following:

When irradiating the straw on 3 points with a Fe55 source, it turned out that L=1.69 m and v=0.260 m/ns. The position x is calculated from x=L-vt/2 , with x in m.

  • The big pulses in straws 1 and 2

    • measured by G.W.van Apeldoorn and T. Sluijk and presented in Cern on 19-2-2002.
  • The big pulses in straws 3 and 4

    • measured by G.W.van Apeldoorn and T.Sluijk and presented in Cern on 19-2-2002.
  • The big pulses in straws 5 and 6

    • measured by G.W.van Apeldoorn and T.Sluijk and presented in Cern on 19-2-2002.
  • For the next measurement the setup is a bit different. The output of the amp ( which is a voltage amplifier of 10 times) is connected to the entrance of a hp54522A scope terminated by 50 Ohm as shown in the next picture.
  • The big pulses in straws 3 and 4

    • measured by G.W.van Apeldoorn and T.Sluijk  with new amps.
  • The plot of fe55 pulses in straws 3 and 4 and in straw 37-38

    • shows the position of the Fe55 source versus time measured by G.W.van Apeldoorn and T.Sluijk  with new amps.
    In this pictures are also shown plots of the ratio of puls heights and charges.
    These ratios follow  a curve that is determined by
    the resistances towards the amplifiers. A fit to this calculated curve is also shown, fit parameter 1 is
    the ratio of the resistances of the wire per mm over 330 Ohm and fit parameter 2 is the total length
    of the straw from amplifier to amplifier.
    The corresponding times and positions are in the file fe55ijkdata
  •  From the plots one can see that the  measurement of time is the most accurate method.
  • With this knowledge one can make pictures of the big pulses in straws and see where they originate from.
  •  Big pulses in straws 35-36  show no special structure. The pulses seem to come from everywhere, no special sources.
  •  Big pulses in straw37-38  show also no special structure but sometimes it was seen on the scope that was a very big one.
  • In  very big pulses in straws 37-38  one sees that they all come from the same place betweeen 85-87 cm from the begin.
  • In the straws 35-40 there are 3 wirelocators, one in the middle and two at the ends. Only in straw 37 one sees that the middle wirelocator gives gigantic pulses. The rate is  less than 0.1 Hz.

    •  
  • To understand the cause of the big pulses , it was suggested to measure the influence of the distance of the wire to the wire locator. If there is a little distance  between the wire and the V of the wire locator ,  the pulses can be generated by a charging up of the surface of the wirelocator. This can be tested in  the setup shown below but without source:
  • Setup with movable straw
  • In the straw half a wire locator is inserted with the V horizontally oriented. By moving the straw the wire can be positioned wrt the V. A micrometer gives the distance to the wire. In this setup the wire locator was at one end of the straw. The length of this straw is 9.0 cm. The gasmix was Ar/CO2 65/35% and the HV was 1700V.
  • In the file  wirelocpos  the results are shown. The wire is at 3.50 mm.Rates are in Hz and charge is in pC. Rates and averaged charge do not show more than 10% effect. It means that the distance between wirelocator and wire is not critically. Also the rates and charges are measured for the same straw without a wire locator. The results are roughly the same:  rate=0.034 Hz and charge=50.7 pC.
  • To be sure the half wirelocator was also put in the middle of the straw. The results are visible in the file    poschratmid.ps  . From this one concludes that the previous results are conformed.
  • This means that the fact if the wire locator touches the wire or not , is not improtant for this type of wire locator. It means also that one does not yet understand why from the 18 wire locators in the 6 tested wires only the one in the middle of straw 37 gives the gigantic pulses.
    • G.W.van Apeldoorn
    Created: Tue March 19 13:32:09 MET DST 2001
    Last modified: Tue Sep 24 16:40:09 MET DST 2001