Straw Characterization Based Upon 55Fe Plateau
Miguel A. Morales
University of Puerto Rico at Mayaguez
SIST Program – Fermilab
Outline
Introduction– Description of the project– Objectives and Motivations– Fundamental Processes
Experimental Setup Results
– Height of the Plateau– Edge Voltage– Gas Gain– Leaks
Conclusions
Introduction
Description of the project– Study of the lower edge of the plateau of the
detector using an 55Fe source.
Objectives and Motivations– Find appropriate parameters with which we could
measure the uniformity and quality of the straws in a detector.
– Develop methods to be used during the detector’s assembly and installation in 2009.
• Fundamental processes
1. A photon produced by the source enters the gas volume and is absorbed.
2. As a consequence of the absorption, two electrons are liberated by the atom.
3. Further electron-ion pairs are produced.
4. The electron cluster drifts toward the wire.
5. Avalanche multiplication occurs, increasing drastically the number of electrons.
Straw
Wire
Primaryelectron cluster
55Fe source
Photon(5.89 keV):
:::
::
::
::
::
::
::
electronsprimary of #
electrons of # totalGain
….
~ 226 e-
~3.2 keV
5.89 keV
~2.69 keV
E
Drifting electrons
Experimental Setup
Detector’s Description– 48 straws– 3 closely packed layers of 16
straws – 4 mm diameter– Composition:
Outer layer: 25 μm Kapton film Inner layer: 25 μm carbon-loaded Kapton film 0.2 μm Al film
– 1 meter long– 25 μm Au-coated W wire– Ar/CO2 (80/20) flows through the
straw volume
Straw Module
4 mm
Au- coated W wire(anode)
25 µm Kaptonfilm
25 µm carbon-loaded
Kapton film 0.2 µm Al layer(cathode)
25 µm
Experimental Setup
25.5 cm
55 Fe source
Straw Module
ASDQBoards
1 m
Source PositionsGas flowing
fromelectronics'
end
Gas flowingtoward
electronics' end
Detector Description (cont.)– The source used was 55Fe.– x-ray energies = 5.89 keV– 25.5 cm from middle layer of
straws– 5 positions along the straw
(from electronics’ end)1. 16.5cm 4. 66 cm2. 35.5 cm 5. 90 cm3. 52 cm
– Flow rates1. 0.4 scfh (standard cubic feet per hour)
2. 0.9 scfh
Straw Prototype Detector
Results
Parameterization of
the plateau curve
2*1*
)(),(
2
21
2
1)(
CDFCDFFit
xdxxCDF
x
ex
Height of the Plateau
Beam distribution is uniform across the layers.
Good parameter to measure uniformity and efficiency.
Strong dependence with straw position in the module.
Edge Voltage
Good parameter to study gain variations across the length of the straw.
Strong dependence with the gain and the threshold of the system.
Values for the prototype ranged between 1090 and 1110 V.
Gas Gain at Edge Voltage
Obtained from previous experiments on the Single Straw Prototype.
Measures the gain needed by the signal to reach the threshold.
Values ranges from 1800 to 2200.
V.e.gain(V) 011200090
Edge Voltage vs Source Position
• Signals produced near the electronics' end travel different distances, reaching the electronics at different times.
Gas Leaks
For normal straws, δ=1 because the edge voltage should not depend on direction of gas flow.
Because of leaks, the gain changes, increasing the edge voltage
For leaky straws, δ < 1.
F
T
EVEV
EVEV
)5.16()90(
)5.16()90(
leakswithoutleakswithEV
EV
EV
EV
)5.16(
)90(
)5.16(
)90(
leakswithoutleakswithEV
EV
EV
EV
)5.16(
)90(
)5.16(
)90(
Gas flowing from electronics:
Gas flowing toward electronics:
Gas Leaks
Leaky Straws are consistent.
Conclusions
Uniformity and Quality– Height of the plateau
Gain Variations– Edge Voltage
Range Found: (1090-1110)
Gas Leaks– Change direction of the gas flow
Acknowledgements
Alan Hahn Penny Kasper
John Krider Bill Pritchard
SIST Committee
Questions???