The active spectroscopy group uses external actuators, such as local gas puffs and neutral beam injection, to excite line emission, which can then be used to diagnose the plasma.
Diagnostic systems within this group include: charge exchange recombination spectroscopy, beam emission spectroscopy, emission spectroscopy on neutral particles, and He spectroscopy. For these last diagnostics, both the form and position of specific spectral lines are analysed as well as the relative intensities of multiple spectral lines emitted by the same population.
These diagnostic systems deliver many important quantities for understanding the plasma behavior including local impurity and main ion temperatures, rotations, and densities, the effective impurity charge, the radial electric field, and scrape off layer (SOL) electron temperatures and densities. Utilizing these measurements the main areas of investigation are:
- Core and edge (pedestal) heat, particle, and momentum transport
- The impact of the pedestal and SOL radial electric field on transport and confinement
- Understanding of filamentary transport and its connection to the pedestal stability and transport