Magnetic Reconnection in High Power Laser-Solid Interactions

In indirect-drive inertial confinement fusion experiments, high power laser beams interact within a hohlraum (a cylindrical gold can) to produce plasmas which radiate x-rays causing compression of a capsule located in the centre of the hohlraum. The production of magnetic fields in these situations can significantly affect the dynamics of the interaction. We have made the first detailed studies of such effects in multiple laser beam geometries using the VULCAN laser facility at the Rutherford Appleton Laboratory in the UK. We have characterized the ablation dynamics and plasma outflows using optical probing and have observed B-field null formation using rear-projection proton probing (see Figure 1). We have also measured strong electron heating via Thomson scattering. The plasma dynamics and estimated magnetic reconnection rates appear consistent with theoretical models. Further experiments are planned using the recently constructed OMEGA EP laser system at the Laboratory for Laser Energetics (LLE) at the University of Rochester.

Fig.1 Proton probing images showing the collision of two magnetized plasmas. The structure in the image is due to the magnetic fields produced during the interaction. The figure on the right shows a magnified view of the central region in which magnetic reconnection is occurring.