GET-ART project: an alternative novel method to measure DT fusion power in magnetic confinement fusion based on detection of 17 MeV gamma rays

The GET-ART (Gamma ray Emission in Tokamaks: Assessment of Reaction rate Throughput) project aims to demonstrate the use of a novel method based on gamma ray detection from the reaction D+T -> 5He+? for the absolute measurements of DT fusion power in tokamaks. The method in use today is based on absolute 14 MeV neutron counting and requires long and time consuming in vessel calibration to benchmark neutron transport simulations from the extended plasma source to the flux monitor detectors (typically fission chambers and activation foils) placed at selected positions around the tokamak. The GET-ART project is studying an alternative method that is based on absolute detection of the weak (~10-5 with respect to neutrons) DT gamma ray emission along a well characterized line of view combined to a neutron camera reconstruction of the neutron/gamma emissivity profiles. This is particular relevant for future DT reactors such as ITER and DEMO where at least two independent methods are required for the licencing of reactors. The presentation will describe the main challenges and solutions identified and the results achieved in the recent DT experiment at JET, where the absolute gamma-ray flux has been measured with a LaBr3 spectrometer installed along an oblique line of sight. JET has an absolute calibration of the 14 MeV neutron emissions which gives the opportunity to assess the neutron to gamma ray DT branching ratio. Finally, the concept and a preliminary design of a new Cerenkov detector optimized for 17 MeV gamma-ray measurements for DT fusion power determination on the next generation tokamak will be presented.