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Thesis: Introduction: WuotD

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documents/thesis/chapters/introduction.tex
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@ -12,7 +12,7 @@
\label{sec:introduction}
% Intro Cosmic Ray
In the beginning of the 20th century, various types of radiation were discovered.
In the beginning of the $\mathrm{20^{th}}$~century, various types of radiation were discovered.
With the balloonflight of Victor Hess \Todo{ref} in \Todo{year}, one type was determined to come from beyond the atmosphere and named ``Cosmic Rays''.
With many discoveries following, the field of (astro-)particle physics evolved.
\\
@ -27,11 +27,11 @@ For such radio arrays, the analyses require an accurate timing of signals within
Generally, \gls{GNSS} is used to synchronise the detectors.
However, advanced analyses require an even higher accuracy.
\\
In this thesis, methods (and their limits) to obtain this accuracy for radio arrays are investigated.
\section{Cosmic Particles}%<<<<<<
%<<<
\label{sec:crs}
Particles from outer space,
Particle type,
@ -45,10 +45,11 @@ There is a variety of extra terrestrial particles with which the Earth is bombar
These can be classified into three main types: charged nuclei (typically protons $Z=1$ up to iron $Z=26$), photons and neutrinos, each with different propagation effects.
\\
The charged nuclei are the bulk of the measured particles.
They do not point back to their sources because they are deflected by magnetic fields due to being charged.
The various magnetic fields that they travel through deflect\Todo{word} them due to their charge.
They do not point back to their sources because of this.
\\
Photons do not suffer from being charged, and thus have the potential to identify their sources.
However, they can be absorbed and created by multiple mechanisms.\Todo{rephrase}
However, they can be absorbed and created by multiple mechanisms.\Todo{rephrase/expand}
\\
Finally, neutrino's interact weakly, thus pointing back to their sources as well.
Unfortunately, this weak interaction also troubles the detection of the neutrino's.\Todo{rephrase}
@ -69,13 +70,13 @@ Note that cosmic rays are deemed\Todo{rephrase} to be charged nuclei.
% Energy
Cosmic rays span a large range of energy as illustrated in Figure~\ref{fig:cr_flux}.
The acceleration of cosmic rays is thought to occur in highly energetic regions
The acceleration of cosmic rays is thought to occur in highly energetic regions\Todo{expand}
\\
Using the charged nuclei, an argument can be made to distinguish two types of sources.
\\
Being charged, the nuclei will gyrate in magnetic fields.
With an approximate size of $ $\Todo{size} and an average magnetic field of $5\mathrm{\;\mu G}$\Todo{}, the Milky Way can only contain particles up to an energy of about $10^{16}\eV$\Todo{fill}.
With an approximate size of $ $\Todo{size} and an average magnetic field of $5\mathrm{\;\mu G}$\Todo{}, the Milky Way can only contain particles up to an energy of about $10^{17}\eV$\Todo{fill}.
Still, particles with higher energies have been observed (see Figure~\ref{fig:}).
These higher energy particles must thus come from beyond our galaxy.
\\
@ -92,18 +93,23 @@ Xmax?,
Radio emission,
\hrule
When a particle with a high enough energy comes into contact with the atmosphere, secondary particles are generated, forming an air shower.
When a particle with an energy above $1\;\TeV$ comes into contact with the atmosphere, secondary particles are generated, forming an air shower.
This air shower consists of a cascade of interactions producing more particles that subsequently undergo further interactions.
Thus, the number of particles rapidly increases further down the air shower.
Figure~\ref{fig:airshower:depth} shows the number of particles as a function of atmospheric depth where $0\mathrm{\; g/cm^2}$ corresponds with the top of the atmosphere.
\\
An important feature that allows to statistically discriminate photons from protons and iron nuclei is the atmospheric depth at which this number of particles reaches its maximum, called $\Xmax$.
Part of this is explained by the depth of first interaction.
Due to the higher charge of heavy nuclei, they interact earlier in the atmosphere.
This happens until the energy is spread out\Todo{word} enough that the number of interactions decreases.
\\
The particle content of an air shower is dependent on the initial particle type.
Protons (and other nuclei) have access to hadronic interaction channels (pions, kaons, etc.)\Todo{ref?} through which most energy is passed.
Figure~\ref{fig:airshower:depth} shows the number of particles as a function of atmospheric depth where $0\;\mathrm{g/cm^2}$ corresponds with the top of the atmosphere.
The atmospheric depth at which this number of particles reaches its maximum is called $\Xmax$.
\\
In Figure~\ref{fig:airshower:depth} the \Xmax is different for a photon, a proton and iron.
Typically, heavy nuclei have their first interaction higher up in the atmosphere than protons, with photons penetrating the atmosphere even further.
Therefore, measurements of $\Xmax$ allow to statistically discriminate between photons, protons and iron nuclei.
\\
The initial particle type also influences the particle content of an air shower.
Protons (and other nuclei) have access to hadronic interaction channels (such as pions, kaons, etc.)\Todo{ref?} through which most energy is passed.
In turn, the resulting air showers contain a large hadronic component.\Todo{check wording}
\\
In contrast, an initial photon cannot interact hadronicly, meaning its energy is dumped into the electromagnetic part of the air shower.
@ -111,7 +117,9 @@ In contrast, an initial photon cannot interact hadronicly, meaning its energy is
Finally, any charged pions created in the air shower will decay into muons while still in the atmosphere.
This muonic component is a reliable part to measure.\Todo{rephrase}
\\
These different components have a different width.\Todo{rephrase}
The hadronic component is greatly collimated, while the electromagnetic component.
\\
\begin{figure}%<<< airshower:depth
\centering
@ -123,44 +131,85 @@ This muonic component is a reliable part to measure.\Todo{rephrase}
\label{fig:airshower:depth}
\end{figure}%>>>
% Radio measurements
Processes in an air showers also generate radiation that can be picked up as coherent radio signals.
%% Geo Synchro
Due to the magnetic field of the Earth, the electrons in the air shower generate radiation.
Termed geomagnetic emission in Figure~\ref{fig:airshower:polarisation}, this has a polarisation that is dependent on the magnetic field vector $B$ and the air shower velocity $v$.
\Todo{expand?}
\\
%% Askaryan / Charge excess
An additional mechanism emitting radiation was first theorised by Askaryan\Todo{ref}.
Due to the large inertia of the positively charged ions with respect to their light, negatively charged electrons, a negative charge excess is created.
In turn, this generates radiation that is polarised radially towards the shower axis (see Figure~\ref{fig:airshower:polarisation}).
\\
%% Cherenkov ring
The relativistic speeds of the particles cause any radiation that is produced in the air shower to be forward beamed along the shower axis.
Additionally, the shower travels faster than the speed of light in the atmosphere.
This generates an
The detection of the radio signals is limited to an
This is limited by the so-called Cherenkov angle.
\begin{figure}%<<< airshower:polarisation
\centering
\begin{subfigure}{0.47\textwidth}
\includegraphics[width=\textwidth]{airshower/airshower_radio_polarisation_geomagnetic.png}%
\caption{
Geomagnetic emission
}
\label{fig:airshower:polarisation:geomagnetic}
\end{subfigure}
\hfill
\begin{subfigure}{0.47\textwidth}
\includegraphics[width=\textwidth]{airshower/airshower_radio_polarisation_askaryan.png}%
\caption{
Askaryan or charge-excess emission
}
\label{fig:airshower:polarisation:askaryan}
\end{subfigure}
\caption{
From \protect \cite{Schoorlemmer:2012xpa} \protect\cite{Huege:2017bqv}
\protect \Todo{Krijn?}
Radio Emission mechanisms (left: geomagnetic, right: charge-excess)
Radio Emission mechanisms: \subref{fig:airshower:polarisation:geomagnetic} geomagnetic and \subref{fig:airshower:polarisation:askaryan} charge-excess)
}
\label{fig:airshower:polarisation}
\end{figure}%>>>>>>
\subsection{Experiments}%<<<
\label{sec:detectors}
%>>>>>>
%\subsection{Experiments}%<<<
%\label{sec:detectors}
\bigskip
At the very highest energy, the flux is in the order of one particle per square kilometer per century (see Figure~\ref{fig:cr_flux}).
To gather decent statistics at these highest energies on a practical timescale, observatories therefore have to span huge areas.
Observatories therefore have to span huge areas to gather decent statistics at these highest energies on a practical timescale.
In recent and upcoming experiments, such as \gls{Auger}, \gls{GRAND} or \gls{LOFAR}, the approach is typically to instrument an area with a sparse grid of detectors to detect the generated air shower.
With distances up to $1.5\;\mathrm{km}$ (\gls{Auger}), the detectors therefore have to operate in a self-sufficient manner\Todo{word} with only wireless communication channels.
\\
The earliest
Standalone detectors typically receive their timing from a \gls{GNSS}.
Previously, for timing of water-Cherenkov detectors, this timing accuracy was better than the resolved data\Todo{rephrase}.
Even for the first analyses of radio data, this was sufficient.
However, for advanced analyses such as radio interferometry, the timing accuracy must be improved.
\\
\hrule
Standalone devices,
\gls*{Auger},
AugerPrime RD,
\gls*{GRAND},
\gls*{LOFAR}?,
% Structure summary
In this thesis, a solution to enhance the timing accuracy of air shower radio detectors is worked out\Todo{word}.
First, introductions to radio interferometry and waveform analysis are given in Chapters~\ref{sec:interferometry}~and~\ref{sec:waveform}.
%>>>>>>
\section{Radio Interferometry}
\cleardoublepage
\chapter{Air Shower Radio Interferometry}
\label{sec:interferometry}
The radio signals emitted from the air shower can be recorded by radio antennas.
The radio signals emitted by the air shower (see Section~\ref{sec:airshowers}) can be recorded by radio antennas.
An array of radio antennas can be used as an interferometer.
Therefore, air showers can be analysed using radio interferometry.
\\
%
Unlike, astronomical interferometry, the source of the signal is closeby.
Unlike, astronomical interferometry, the source of the signal is closeby, therefore
\begin{figure}
@ -202,6 +251,8 @@ Unlike, astronomical interferometry, the source of the signal is closeby, theref
\label{fig:trace_overlap}
\end{figure}
\begin{figure}
\centering
\includegraphics[width=0.7\textwidth]{2006.10348/fig03_b.png}%
@ -234,4 +285,7 @@ Need reference system with better accuracy to constrain current mechanism (Figur
% \label{fig:reference-clock}
%\end{figure}
\end{document}