JET-P(91)27
LIDAR Thompson Scattering – Report on IAEA Technical Committee Meeting JET 8-l0th April 1991
This Technical Committee Meeting report is intended as a review for those readers who are not necessarily specialists in this particular plasma diagnostic technique. Thomson scattering was first used to measure electron temperatures and densities in magnetically confined plasma during the mid 1960's. Since that time with the improvements in laser and detector technologies the technique has become one of the essential standard diagnostic techniques for making spatially resolved temperature and density profile measurements in fusion research. The increase in dimensions of confinement experiments combined with technological developments in a number of key areas, namely high energy short pulse (sub-nanosecond) lasers; fast, high gain detectors; high bandwidth recording techniques: made it possible in the early 1980's to consider a departure from the standard 90° scattering geometry for the spatial profile systems and to use instead, a time of flight backscattering or LIDAR (Light Detection And Ranging) technique. A short laser pulse is launched through the plasma and its progress· is monitored by observing the light backscattered from the plasma electrons. The spectrum and total scattered intensity give the electron temperature (Te) and density (ne) in the normal way for Thomson scattering but their profiles are also determined since the position of the laser pulse is known by the time of flight principle. In addition LIDAR-Thomson scattering offers a considerable simplification of the alignment and access requirements, increasingly important factors when diagnostics for the next step fusion machines are being considered. The meeting was divided broadly into four sections; the first was a short session in which the existing JET LIDAR system was reviewed and advanced plans for a higher resolution extension were presented; the second was devoted to lasers and laser developments; the third dealt mostly with fast detectors and analysis techniques; in the final section the outline designs of LIDAR scattering systems for new fusion machines were discussed