Schematic view of the experimental set-up. A plasma is generated from a plasma gun or a laser-ablated Teflon (CF₂) target. It expands into the vacuum (along z as the main expansion axis), which is embedded in a strong external magnetic field, orientated along x. Because of the imposed magnetization, the plasma is progressively flattened out along y, while it can flow along the magnetic field line (i.e. along x). Hence, it progressively morphs into a ‘pancake’, as depicted.