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???