Multiphysics approach to plasma neutron source modelling at the JET tokamak

Abstract

A novel multiphysics methodology for the computation of realistic plasma neutron sources has been developed. The method is based on state-of-the-art plasma transport and neutron spectrum calculations, coupled with a Monte Carlo neutron transport code, bridging the gap between plasma physics and neutronics. In the paper two JET neutronics tokamak models are used to demonstrate the application of the developed plasma neutron sources and validate them. Diagnostic data for the record JET D discharge 92436 are used as input for the TRANSP code, modelling neutron emission in two external plasma heating scenarios, namely using only neutral beam injection and a combination of the latter and ion cyclotron resonance heating. Neutron spectra, based on plasma transport results, are computed using the DRESS code. The developed PLANET code package is employed to generate plasma neutron source descriptions and couple them with the MCNP code. The effects of using the developed sources in neutron transport calculations on the response of JET neutron diagnostic systems is studied and compared to the results obtained with a generic plasma neutron source. It is shown that, although there are significant differences in the emissivity profiles, spectra shape and anisotropy between the neutron sources, the integral response of the time-resolved ex-vessel neutron detectors is largely insensitive to source changes, with major relative deviations of up to several percent. However it is calculated that, due to the broadening of neutron spectra as a consequence of external plasma heating, larger differences may occur in activation of materials which have threshold reactions located at DD neutron peak energies. The PLANET plasma neutron source computational methodology is demonstrated to be suitable for detailed neutron source effect studies on JET during DT experiments and can be applied to ITER analyses.

Overview of interpretive modelling of fusion performance in JET DTE2 discharges with TRANSP

“…It is the neutron activation system that is absolutely validated in the calibration procedure due to its proximity to the plasma source, while the fission chambers are cross-calibrated against it. The complex and state-of-the-art procedure, which requires detailed neutron transport calculational support and dedicated plasma calibration discharges, has a total uncertainty below ∼10% and is planned to be applied to ITER [6][7][8][9]. In this work we exploit the absolute neutron yield measurements obtained in DTE2 to benchmark state-ofthe-art plasma code calculations, and provide a foundation to validate and tune predictive models.…”

Long Term Neutron Activation in JET DD Operation

“…The neutron emissivity profile used for calculations was taken from a pre-computed TRANSP plasma transport simulation for a NBI heated JET plasma [16,17]. As in the DD plasma some DT neutrons are produced due to the burnup of tritium generated in the DD reactions, therefore the neutron source used for computational support was a combination of DD and DT neutron sources [18].…”

Analytical and MonteCarlo approaches to infer the total gamma ray emission from the JET tokamak

“…For this work, the neutron emission profile was both measured with the neutron camera diagnostics [7] and, in order to benchmark the reconstructed profile, estimated numerically based on the plasma heating configuration and a number of measured plasma parameters given as input to the TRANSP [8] code. In this second case, a prediction of the neutron emission profile in the 3D space is obtained as output [9,10], whose projection in the poloidal plane for deuterium-tritium JET pulse #99608 at time 𝑡 = 47 s is shown on the right in figure 1. Discharge #99608 was a deuterium-tritium pulse part of the 3-ion scenario experiment [11,12] with a neutron yield of about 10 17 neutrons per second whose most significant plasma parameters are given in [5].…”