The effect of adding an axial magnetic field on the expansion of a laser-produced plasma

We use a pulsed ultraviolet laser to ablate a copper target in order to study the effects of adding a permanent and axial magnetic field on the plasma plume expansion. The laser pulse duration is 20 ns, its energy is 150 mJ, and it is focused on a surface of about 1 mm2. The target is inserted at the center of a ring permanent neodymium magnet as we compare data taken with and without the magnetic field using a Langmuir probe that is installed at 2.5 cm from the target but is capable of moving radially. The magnetic field, B, affects the plasma plume by reducing its expansion and by increasing the plasma temperature significantly. We report, and for the first time, the measurement of the average axial as well as the radial electric fields and show that both are enhanced in the presence of a magnetic field. This yields a strong increase in the plasma current and thus that of ohmic heating, which could help in explaining the temperature increase recorded by different groups when a magnetic field is added to the plasma plume expansion.