Laser-plasma expansion into a preformed magnetized plasma

The expansion of an energetic laser-produced plasma across the magnetic field (0.1-1 kG) in a large (1 m x 17 m) magnetized plasma (He, 4x10$^{12}$ cm$^{-3}$, 5 eV) is studied by means of magnetic pickup coils and fast shutter photography. The bulk blow-off velocity of the laser-plasma is initially larger than the Alfv\'{e}n velocity. The laser plasma radiates large amplitude Alfv\'{e}n waves. We will present measurements of the compression and amplification of the magnetic field at the edge of the diamagnetic cavity.