A simple experimental method to determine magnetic field topology in toroidal plasma devices.

Estimation of the parallel wavenumber in plasma devices finds wide applications such as determining the nature of instabilities. This task is often challenging, especially in toroidal magnetic configurations. In the present work, a simple yet effective method of achieving accurate probe-alignment along the magnetic field lines is demonstrated in a simple magnetized toroidal device BETA (Basic Experiments in Toroidal Assembly). The alignment was achieved by aligning each probe to a tiny localized plasma source. Such an alignment is necessary for determining the parallel wavenumber precisely. The probe-alignment was confirmed further from the measurements in the plasma and the corresponding parallel wavenumber was found to be in good agreement with the analytical predictions.