Speaker
Federico Binda
(Physics and Astronomy)
Description
The signal of a neutron detector can be divided into an unscattered and a scattered component. In fusion, the unscattered, direct component reaches the detector directly from the fusion plasma. The scattered neutrons, on the other hand, reach the detector after interacting with some of the materials in the fusion device. More specifically, the backscatter component is defined as the signal from neutrons that are scattered in the wall of the tokamak directly opposite to the neutron detector. Backscattered neutrons can contribute significantly to the total neutron rate seen by a neutron detector and it is therefore important to accurately estimate their energy distribution and rate.
Previously the calculation of the backscatter component was done by first estimating the expected direct emission and then multiplying it with an energy dependent neutron backscatter matrix. The latter was obtained by combining many MCNP simulations of the backscattered neutron energy distribution for monoenergetic neutron emission, each simulation with a different energy. However this method neglects the fact that the backscatter component can depend on the neutron emissivity profile.
Here we take profile effects into account by producing a neutron backscatter matrix that is profile dependent (instead of energy dependent). This is done by dividing the plasma source into toroidal voxels in the MCNP simulation and constructing the matrix from the backscattered neutron energy distribution from each voxel. The backscatter component is then obtained by multiplying the emissivity profile with the matrix.
We apply this method to calculate the neutron backscatter matrix for the neutron camera detectors at JET.
We then use the matrix to evaluate the backscatter component for different neutron emissivity profiles, showing that they produce different results. We conclude that this method improves the evaluation of the neutron backscatter component and should be used for future analyses of the neutron emission.
Co-authors
Erik Andersson Sunden
(Physics and Astronomy, Uppsala University, Uppsala, Sweden)
Federico Binda
(Physics and Astronomy, Uppsala University, Uppsala, Sweden)
Goran Ericsson
(Physics and Astronomy, Uppsala University, Uppsala, Sweden)
Sean Conroy
(Physics and Astronomy, Uppsala University, Uppsala, Sweden)
contributors JET
(EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
