Laser produced plasma expansion into high magnetic field gradients.

Laser produced plasmas expanding into background magnetic fields is a good analogue for many plasma phenomena. We have extended our previous work by initiating a laser produced plasma expansion into a nonuniform, high gradient background magnetic field. The highly uniform magnetic fields produced by the Magnetized Dusty Plasma Experiment (MDPX) were combined with the field of 2” x 2” cylindrical permanent magnet to create our desired fields within a vacuum chamber pumped to pressures of ~ 4 mTorr. We captured the emission from the laser ablating a solid carbon fiber sheet with an ICCD camera, and the input laser energy, applied MDPX field, and camera gate delay time relative to the laser pulse were all varied. Increasing laser energy led to a broadening of the plasma emission transverse to the magnetic field and increasing the applied MDPX field led to a focusing of the plasma emission. Varying the camera gate delay allowed us to observe the dynamics of the expansion, and the resultant gradient field also lead to a much longer confinement time than that of laser produced plasmas expanding directly transverse to the applied magnetic field with the emission lifetime lasting upwards of 10 μs. Additionally, the plasma emission seemed to have two distinct components with one fast lived component reaching maximum expansion within 1 μs and another slower component reaching maximum expansion at > 10 μs.