Design Studies on the Detection of Air Showers with the Radio Air Shower Test Array

129 Pages·2012·12.48 MB·English

by  Markus Vehring

Design Studies
on the Detection of Air Showers
with the Radio Air Shower Test Array
(RASTA)
at the South Pole
von
Markus Vehring
Diplomarbeit in P H Y S I K
vorgelegt der
Fakultät für Mathematik, Informatik und
Naturwissenschaften
der Rheinisch-Westfälischen Technischen Hochschule Aachen
im
Mai 2011
angefertigt am
III. Physikalischen Institut B
Prof. Dr. Christopher Wiebusch

Abstract
The Radio Air Shower Test Array (RASTA) is a project
for the possible detection of air showers by their in-
duced synchrotron radiation. Radio emissions due to
the geosynchrotron effect are expected especially for
theelectromagneticcomponentoftheshowermaximum.
The detection of this radiation is a promising possibil-
ity for a cost-efficient air shower detector with a high
acceptance and a high duty cycle.
The RASTA project aims to extend the existing
IceCubeandIceTopdetectorsatthegeographicSouth
Pole with another detector component. This hybrid de-
tector will provide complementary information about
the detected air showers. The deployment at the South
Pole imposes special demands on the construction and
electric characteristics of the used antennas.
In this thesis different models of antennas for the de-
ployment at Antarctica were simulated and compared
to each other. A prototype antenna was built for the
most promising model to compare the simulation results
with experimental data. The results show consistence
between measurement and simulation. The main an-
tenna characteristics and properties are understood af-
ter the study of systematic effects. Furthermore, a sim-
ple dipole antenna was constructed and shipped to the
South Pole, to measure the electromagnetic background
at the possible site of deployment. Although the mea-
surement showed to be more difficult than expected, it
was possible to extract the electromagnetic background
at the possible site of the later deployment.

Note
Thisisarevisedversionoftheoriginalthesis. Twosmall
errors have been corrected in this release. The intrinsic
impedance of a medium in section 6.1.5 was corrected
from nZ to n/Z . It has to be stated, that this error
0 0
was limited to this section and had no impact on the
following chapters. Furthermore, figure 9.1a showed the
integrated intensity for a solid angle of 2π. This was
also corrected.
iii

Contents
Abstract i
1 Introduction 1
2 Theory of Ultra High Energy Cosmic Rays 3
2.1 Early Discoveries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Cosmic Rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Lower Energy Particles . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Acceleration of Cosmic Rays and Galactic Sources . . . . . . . . . . 5
2.2.3 Sources for Ultra High Energy Cosmic Rays (UHECR) . . . . . . . 6
2.3 Composition and Energy Spectrum . . . . . . . . . . . . . . . . . . . . . . 7
3 Cosmic Ray Induced Air Showers 11
3.1 Shower Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2 Radio Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.1 Radio Emission of EAS . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.2 Simulation of Radio Emission from EAS . . . . . . . . . . . . . . . 16
4 IceCube 19
4.1 The InIce Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 IceTop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2.1 First IceTop Measurements . . . . . . . . . . . . . . . . . . . . . . 23
5 Radio Detection 27
5.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.1 Veto Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.2 UHE Gamma Rays . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.3 Measurement of the Cosmic Ray Flux Composition . . . . . . . . . 28
5.2 Demands for Antennas at the South Pole . . . . . . . . . . . . . . . . . . . 29
6 Antenna Theory and Simulation 31
6.1 Antenna Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.1.1 Directivity and Gain . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.1.2 Reflection Coefficient and VSWR . . . . . . . . . . . . . . . . . . . 33
6.1.3 Antenna Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.4 Maximum Power Transfer . . . . . . . . . . . . . . . . . . . . . . . 34
6.1.5 Antenna in Reception Mode . . . . . . . . . . . . . . . . . . . . . . 35
6.1.6 Transmission between two Antennas . . . . . . . . . . . . . . . . . 36
6.1.7 RF Transformers and Baluns . . . . . . . . . . . . . . . . . . . . . 37
v
Contents
6.2 Antenna Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.1 Simulations for a Half-Wave Dipole . . . . . . . . . . . . . . . . . . 38
6.2.2 Differences between NEC2/NEC4 and FEKO . . . . . . . . . . . . 41
7 Antenna designs 45
7.1 Existing antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.2 Simulated Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.2.1 The Fat Wire Dipole . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.2.2 Logarithmic Periodic Dipole Antennas . . . . . . . . . . . . . . . . 48
7.2.2.1 Design of a LPDA . . . . . . . . . . . . . . . . . . . . . . 48
7.2.2.2 Meander Shape V-LPDA . . . . . . . . . . . . . . . . . . 50
7.2.3 The Butterfly Antenna . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.3 Results from Antenna Simulations . . . . . . . . . . . . . . . . . . . . . . . 52
7.4 Pulse Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.4.1 Principle of the Pulse Simulation . . . . . . . . . . . . . . . . . . . 56
7.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8 Measurement of a Prototype Antenna Model 63
8.1 Design of a Scale Size Prototype Model and Emitter Dipoles . . . . . . . . 64
8.2 First Tests of the Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . 66
8.2.1 Noise Level at the Test Site . . . . . . . . . . . . . . . . . . . . . . 70
8.3 Measurements of the Transmission Between the Prototype and a Test An-
tenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
8.3.1 Measurement Inside the Physics Experiment Hall . . . . . . . . . . 72
8.3.2 Measurement Outdoors . . . . . . . . . . . . . . . . . . . . . . . . . 73
8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
9 Noise Measurement at the South Pole 79
9.1 Galactic Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
9.2 Design of an Antenna for the Measurement of Radio Noise . . . . . . . . . 81
9.3 Data Taken at the South Pole . . . . . . . . . . . . . . . . . . . . . . . . . 82
9.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
9.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
10 Summary and Outlook 89
A Equations 91
A.1 Decibel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
A.2 Dielectric Properties of Snow . . . . . . . . . . . . . . . . . . . . . . . . . . 91
B Antenna designs 93
vi
Contents
C Plots 95
C.1 Chapter 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
C.2 Chapter 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
C.3 Chapter 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
C.4 Chapter 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
D Data sheets 102
References I
List of Figures VII
List of Tables XII
Acknowledgements XIII
Erklärung / Declaration XV
vii