Internal B field measurements using Pulsed Polarimetry on TAE's future Copernicus device

Copernicus will be the next generation field reversed configuration (FRC) device at TAE Technologies. Heated and sustained by neutral beam injection, the plasmas are expected to reach D-T relevant parameters. Recently, the production of intense sub-picosecond far-infrared (FIR) pulses has been demonstrated using 100 TW class lasers on material targets, allowing the implementation of a pulsed polarimeter diagnostic. Pulsed polarimetry is a Lidar technique that combines the two well-known diagnostic techniques of Thomson scattering and polarimetry to provide profiles of n_e(s), T_e(s) and B_||(s) along the laser sightline. The rate of change of the Faraday angle, alpha, with distance, d(alpha)/ds, is directly proportional to the local [n_eB_||(s)] product. An outstanding issue with FRCs is a direct measurement of reversed flux, if the d(alpha)/ds profile changes sign with density constant then B_|| is reversed. In Copernicus, line integrated Faraday rotation angles of a few tens of degrees are expected for a laser wavelength of 150 microns allowing a spatial resolution of local B_|| to 10cm in a practical system. The diagnostic technique and the intricacies of the laser source, optics and detection of FIR backscatter will be presented and discussed.