Prediction/modelling of the neutron emission from JET discharges

Abstract

The neutron emission from the JET tokamak is investigated using an extensive set of diagnostics, permitting the instantaneous neutron yield, the radial profile of the neutron emission and neutron energy spectra to be studied. Apart from their importance as an immediate indication of plasma fusion performance, the customary use for neutron measurements is as a test of the internal consistency of the non-neutron diagnostic data, from which the expected neutron production can be predicted. However, because contours of equal neutron emissivity are not necessarily coincident with magnetic flux surfaces, a fully satisfactory numerical analysis requires the application of highly complex transport codes such as TRANSP. In this paper, a far simpler approach is adopted wherein the neutron emission spatial profiles are used to define the plasma geometry. A two-volume model is used, with a core volume that encompasses about 2/3 of the neutron emission and the peripheral volume the remainder. The overall approach provides an interpretation of the measured neutron data, for both deuterium and deuterium-tritium plasma discharges, that is as accurate as the basic non-nuclear plasma data warrant. The model includes the empirical assumption that particles, along with their energies and momenta, are transported macroscopically in accordance with classical conservation laws. This first-order estimate of cross-field transport (which, for deuterium-tritium plasmas, determines the d:t fuel concentration ratio in the plasma core), is fine-tuned to reproduce the experimental ion and electron temperature data. The success of this model demonstrates that the observed plasma rotation rates, temperatures and the resulting neutron emission can be broadly explained in terms of macroscopic transport.

Beam-ion confinement for different injection geometries

“…Measured neutron rates agree with predictions based on these theories. In the last decade, many new techniques and devices have reconfirmed this basic picture [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

Technological exploitation of the JET neutron environment: progress in ITER materials irradiation and nuclear analysis

“…The inset neutron spectrum, shown in figure 4, exhibits the two characteristic neutron energy peaks from the D-D and D-T fusion reactions. Although the principal operation mode of JET was in D-D plasma mode in this campaign, resulting in the production of neutrons around 2.45 MeV, the triton produced from one branch of this reaction leads to 14 MeV neutrons being present in the field through subsequent D-T reactions [25,26]. For the FISPACT-II inventory calculations MCNP-derived pointwise spectrum-averaged cross sections were used as input for all dosimetry reaction channels; IRDFF-II [27] pointwise data were used where possible, JEFF 3.3 pointwise data were used otherwise.…”

Activation of ITER materials in JET: nuclear characterisation experiments for the long-term irradiation station

“…Figure 4 shows the predicted activity results obtained from the activation calculations, along with some of the key inputs to the calculation. Figure 4 around 2.45 MeV, the triton produced from one branch of the D-D fusion reaction leads to 14 MeV neutrons being present in the field from D-T reactions, which is reported to be typically 1% in JET according to [16,17]. This assumed value of 1% has been adopted in our activation calculations.…”

“…The inset neutron spectrum shown in 4(b) exhibits the two characteristic neutron energy peaks from the D-D and D-T fusion reactions. Although the principal operation mode of JET was D-D in this campaign, resulting in the production of neutrons around 2.45 MeV, the triton produced from one branch of the D-D fusion reaction leads to 14 MeVneutrons being present in the field from D-T reactions, which is typically 1% in JET[16,17].…”