Digital holographic interferometry for diagnosing the density profile of laser-produced collisionless shock.

A digital holographic interferometry based on Fresnel biprism has been developed to measure the electron density profile of laser-produced collisionless shocks in laboratory, which used the Fourier transform method to solve the wrapped phase. The discontinuous surfaces of shocks will produce the break and split of the interference fringes, which cannot be processed by the conventional path-following phase unwrapping algorithm when reconstructing the real phase of the plasma. Therefore, we used a least-squares method to extract the real phase, which is proportional to the line-integrated electron density. We obtained fine density profiles of collisionless shocks in the line-integrated density region around 1018 cm-2 with a density resolution of 3.38 × 1016 cm-2. The shock structure is in well agreement with that measured by the dark-field schlieren methods and that predicted by shock jump condition. Synthetic holograms are used to confirm the effectiveness of our algorithm, and it is shown that correct results can still be obtained even if part of the diagnostic light is refracted out of the optical system by the shock.

Pulsed magnetic field device for laser plasma experiments at Shenguang-II laser facility.

A pulsed intense magnetic field device was developed for the Shanghai Shenguang-II (SG-II) laser facility. The device using a double-turn coil with 12 mm diameter is capable of producing a peak current of 42 kA with 280 ns rising edge and 200 ns flat top width. A peak magnetic field of 8.8 T is achieved at the center of the coil. A two-section transmission line composed by a flexible section and a rigid section is designed to meet the target chamber environment of SG-II laser facility. The flexible section realizes the soft-connection between the capacitor bank and the target chamber, which facilitates the installation of the magnetic field device and the adjustment of the coil. The rigid section is as small as possible so that it can be inserted into the target chamber from any smallest flange, realizing elastic magnetic field configuration. The magnetic coil inside the chamber can be adjusted finely through a mechanical component on the rigid transmission line outside the target chamber. The adjustment range is up to 5 cm in both radial and axial directions with ∼50 µm precision. The device has been successfully operated on SG-II laser facility.