Development of a Faraday polarimeter for magnetic field measurements in a discharge channel for ion beam transport

An alternate technique for heavy ion beam transport inside the chamber of an inertial confinement fusion reactor, is by the use of a self standing Z-pinch discharge. The focusing properties of such a channel are determined by the magnetic field distribution inside the plasma column. In order to allow measuremets of the magnetic field in the LBNL channel experiment, a Faraday polarimeter has been developed, consisting of a high power cw CO2 laser (10.6 μm) and two HgCdTe detectors working on the half-shadow principle. The polarimeter was designed for a sensitivity of 0.01° since the expected peak rotation was only about one degree. Preliminary measurements with reduced sensitivity indicate that the current flow is confined within a small cylinder of ca. 1 cm diameter.