% Thanks to Jake: http://tex.stackexchange.com/a/142815/5645
\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows}

\begin{document}
\begin{tikzpicture}
    \draw [red] (0,0) circle [radius=1];
    \draw [domain=1:18.8,variable=\t,smooth,samples=200,->,>=stealth']
        plot ({\t r}: {1+2*exp(-0.1*\t)});
\end{tikzpicture}
\end{document}
