A blog of Python-related topics and code.
Rotating text onto a line in Matplotlib
Posted by: christian on 3 Sep 2018
Sometimes it is necessary to rotate a text annotation in a Matplotlib figure so that it is aligned with a line plotted on the figure Axes. Axes.annotation takes an argument, rotation, to allow a text label to be rotated, and a naive implementation might be as follows:
Types of plasma
Posted by: christian in Featured on frontpage on 2 Sep 2018
Two important parameters in plasma physics are the electron Debye length, $\lambda_{\mathrm{D}e}$, a measure of the distance over which charge-screening effects occur and deviations from quasi-neutrality are observed, and the number of paricles in a "Debye cube" (of side length $\lambda_{\mathrm{D}e}$), $N_\mathrm{D}$.
The Debye length
Posted by: christian on 21 Aug 2018
An important concept in plasma physics is the Debye length, which describes the screening of a charge's electrostatic potential due to the net effect of the interactions it undergoes with the other mobile charges (electrons and ions) in the system. It can be shown that, given a set of reasonable assumptions about the behaviour of charges in the plasma, the electric potential due to a "test charge", $q_\mathrm{T}$ is given by $$ \phi = \frac{q_\mathrm{T}}{4\pi\epsilon_0 r}\exp\left(-\frac{r}{\lambda_\mathrm{D}}\right), $$ where the electron Debye length, $$ \lambda_\mathrm{D} = \sqrt{\frac{\epsilon_0 T_e}{e^2n_0}}, $$ for an electron temperature $T_e$ expressed as an energy (i.e. $T_e = k_\mathrm{B}T_e'$ where $T_e'$ is in K) and number density $n_0$. Rigorous derivations, starting from Gauss' Law and solving the resulting Poisson equation with a Green's function are given elsewhere (e.g. Section 7.2.2. in J. P. Freidberg, Plasma Physics and Fusion Energy, CUP (2008)).
A simple colouring grid
Posted by: christian on 15 Aug 2018
Just a simple Python app to try out the TkInter interface to the Tk GUI toolkit and to keep my children occupied. It shows a window with a square grid of cells which can be coloured by selecting from a palette. Run with
Plotting nuclear fusion cross sections
Posted by: christian in Featured on frontpage on 10 Jul 2018
In a nuclear fusion reaction two atomic nuclei combine to form a single nucleus of lower total mass, the difference in mass, $\Delta m$ being released as energy in accordance with $E = \Delta m c^2$. It is this process which powers stars (in our own sun, hydrogen nuclei are fused into helium), and nuclear fusion has been actively pursued as a potential clean and cheap energy source in reactors on Earth for over 50 years.