Abstract
A scintillator-based energetic ion loss detector has been successfully commissioned on the Alcator C-Mod tokamak. This probe is located just below the outer midplane, where it captures ions of energies up to 2 MeV resulting from ion cyclotron resonance heating. After passing through a collimating aperture, ions impact different regions of the scintillator according to their gyroradius (energy) and pitch angle. The probe geometry and installation location are determined based on modeling of expected lost ions. The resulting probe is compact and resembles a standard plasma facing tile. Four separate fiber optic cables view different regions of the scintillator to provide phase space resolution. Evolving loss levels are measured during ion cyclotron resonance heating, including variation dependent upon individual antennae.
Highlights
The tokamak concept1 of energy production through nuclear fusion requires the magnetic confinement of fusionproduced energetic particles such that the plasma becomes self-heated
This paper describes the first FILDtype diagnostic system to be installed and operated on C-Mod for the explicit purpose of detecting lost energetic ions resulting from ion cyclotron resonance heating (ICRH) in the H-minority scenario
Interesting fast ion loss behavior has been measured during the commissioning of this diagnostic, including increased signals from a specific ICRH antenna
Summary
The tokamak concept of energy production through nuclear fusion requires the magnetic confinement of fusionproduced energetic particles such that the plasma becomes self-heated. The energetic ion population is of great interest for its effects on the confined plasma in addition to possible wall damage. This kinetic population is capable of inducing global effects such as poloidal asymmetries in impurity density.. The high magnetic field of C-Mod previously allowed for the development of charged fusion product probes.. The high magnetic field of C-Mod previously allowed for the development of charged fusion product probes.21,22 These were successfully applied to the measurement of fusion rates and the determination of ion temperatures, but noise and sensitivity issues limited the range of operating parameters over which this was possible.. Simplifying design choices have been implemented, the resulting detector is measuring lost ICRH tail ions, and a series of upgrades are identified to significantly improve this system in the near future
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