# TikZ: bad endpoint with "snake it" arc

I'm trying to draw a simple diagram of the type showed in the picture below. I need an arc with a wiggle line. Using proper decoration packages, the option \draw [decorate,decoration=snake] does the wiggly line, but the endpoints of the arc are poorly done -- see the picture.

Here I link the code I'm currently using:

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{decorations.pathmorphing}
\begin{document}

\begin{figure}
\begin{center}
\tikzpicture [scale=0.9, line width=0.30mm]
\draw[decorate,decoration=snake](0.92,0) arc (0:180:0.92);
\draw[dashed](-1.5,0)node[left]{$p$}--(1.5,0)node[right]{$-p'$};
\draw[decorate,decoration={coil,amplitude=4pt, segment length=5pt}](0,1)--(0,2.2)node[above]{$k_0$};
\endtikzpicture
\end{center}
\end{figure}

\end{document}


Does anyone know how to fix it? Thanks for the help!

• Is the issue the connection between the coil and the snake or between the snake and the dashed line? Jan 19 at 1:48
• The issue was in the connection with the dashed line, the vertex on the left in my picture has the wiggly line poorly attached. The solution proposed below works perfectly! Jan 19 at 13:16

You can draw the snake so it starts and ends well below the dashed line. Then clip is so only the part above the line appears:

It's unclear how you want the coil to attach.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{decorations.pathmorphing}
\begin{document}

\begin{figure}
\begin{center}
\tikzpicture [scale=0.9, line width=0.30mm]
\begin{scope}
\clip(-2,0)rectangle(2,2);
\draw[decorate,decoration={snake}](-33:.92) arc (-33:210:.92);
\end{scope}
\draw[dashed](-1.5,0)node[left]{$p$}--(1.5,0)node[right]{$-p'$};
\draw[decorate,decoration={coil,amplitude=4pt, segment length=5pt}](0,1)--(0,2.2)node[above]{$k_0$};
\endtikzpicture
\end{center}
\end{figure}

\end{document}

• This was exactly the issue, thanks! The attachment of the coil is fine as the one you showed in your picture, I don't know if there's a better way to do it. Jan 19 at 13:15
• You could try changing the pre length and post length of the coil, e.g.: \draw[decorate, decoration={coil, amplitude=4pt, segment length=5pt, pre length=1.5mm, post length=1mm}](0,.94)--(0,2.2)node[above]{$k_0$}; Jan 19 at 13:50
• Perfect, it's even nicer! Jan 20 at 10:36