1. National Technical University of Athens Faculty of Applied Sciences
Simulation study of the ATLAS Muon Drift Tube Chambers performance in presence of magnetic field
Mermigka Kalliopi
National Technical University of Athens
Faculty of Applied Sciences
Department of Physics
Ioannina, April 2006

2. Mermigka Kalliopi - N.T.U.A.
ATLAS Experiment
Muon Drift Tube
ATLAS detector
Operation Principle
Drift Time Spectrum
Muon Drift Chamber
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

3. Mermigka Kalliopi - N.T.U.A.
Outline
Detailed simulation studies have been performed investigating the drift properties of the nominal MDT gas (Ar/CO2-93/7) in presence of magnetic field.
Results of the effect of magnetic field varying from 0.1 T to 1.4 T on muon tracks passing at different distances from the tube anode wire will be discussed.
The reliability of the simulation program -Garfield with Magboltz- has been verified with comparisons of precision measurements in the bibliography. It is the first time of validation with magnetic field against to the measurements.
- NIM A324 (1993) , T. Kunst, B. Gotz, B. Schmidt
- NIM A398 (1997) , X. Bittl, V. Fessler, et al.
The only measurements in ATLAS with magnetic field done by
O. Kortner, C. Valderanis, MPI, not published yet
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

4. Mermigka Kalliopi - N.T.U.A.
Garfield Simulation
The drift time of electrons depends on:
gas composition,
temperature,
pressure variations and
magnetic field.
We will show this dependence in presence and absence of magnetic field.
Garfield is a computer program for the detailed simulation of two- and three-dimensional drift chambers.
Magboltz provides the computation of electron transport properties in gas mixtures under the influence of electric and magnetic fields.
We have used the newest Garfield 9 with Magboltz 7.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

5. Typical Events in Garfield simulation
Muon Track
Muon Track
Electron drift lines
Electron drift lines
Ion drift lines
Ion drift lines
NO magnetic field
Magnetic field of 3T parallel to the wire
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

6. Mermigka Kalliopi - N.T.U.A.
Gas Composition
Temperature 20 °C – Pressure 3 bar
NO magnetic field
Magnetic field 0.5T parallel to the wire
The maximum drift time decreases (↓) up to 3% of CO2 and then increases (↑).
For higher percentages of CO2 the cross section goes up (↑), the mean free path goes down (↓) and consequently the drift time increases (↑).
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

7. Temperature Effect Ar/CO2 (93:7) – Pressure 3 bar NO magnetic field
Magnetic field 0.5 T parallel to the wire
According to gas equation P=(n/V)RT and Pressure (P)=constant:
Temperature (T) (↑) number of molecules per volume (n/V) (↓)
the mean free path (↑) and the maximum drift time (↓).
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

8. Pressure Effect Ar/CO2 (93:7) – Temperature 20 °C NO magnetic field
Magnetic field 0.5T parallel to the wire
According to gas equation P=(n/V)RT and Temperature (T)=constant:
Pressure (P) (↑) number of molecules per volume (n/V) (↑)
the mean free path (↓) and the maximum drift time (↑).
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

9. Mermigka Kalliopi - N.T.U.A.
ΔT vs. r
P. Bagnaia, G. Volpi
The parallel component of the magnetic field in the ATLAS muon spectrometer. The position of the MDT chambers is shown.
The maximum drift time differences due to a magnetic field B, parallel to the wire, as a function of the distance r between the track and the anode wire.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

10. Reliability of simulation program
It is the first time of validation with magnetic field against to the measurements.
Two components of the drift velocity:
(uz) parallel to the electric field,
(ux) perpendicular to both the electric and magnetic field.
One can specify the absolute value of the drift velocity (u) and tan a = ux / uz, where a is called the Lorentz angle.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

11. Reliability of simulation program
Left side: Drift velocity in 90% Ar + 10% CH4 with magnetic field 2 Hx (=B/N).
Right side: Lorentz angle in 90% Ar + 10% CH4 with magnetic field 2 Hx.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

12. Reliability of simulation program
Left side: Drift velocity in 90% Ar + 10% CH4 with magnetic field 20 Hx (=B/N).
Right side: Lorentz angle in 90% Ar + 10% CH4 with magnetic field 20 Hx.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

13. Mermigka Kalliopi - N.T.U.A.
Summary
Maximum drift time dependence:
Higher percentages of CO2 tm (↑)
Temperature (↑) tm (↓)
Pressure (↑) tm (↑)
Garfield with Magboltz is a good simulation tool for the study of MDT Chambers in presence of magnetic field.
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.

14. Mermigka Kalliopi - N.T.U.A.
Acknowledgements
I would like to thank:
University Professor, Evangelos N. Gazis
Dr Rachel-Maria Avramidou, and
Dr Rob Veenhof
HEP 2006, 16 April
Mermigka Kalliopi - N.T.U.A.