The aim is to assess the feasibility of triton burn-up studies at the stellarator Wendelstein 7-X (W7-X) with an existing scintillating fiber neutron detector, SciFi. Models are used to estimate ...triton burn-up and corresponding neutron rates from deuteron (DD) fusion and deuteron-triton (DT) fusion in future deuterium plasmas of W7-X for fast-ion confinement studiesSciFi is equipped and commissioned with a new digital data acquisition system, which is capable of determining pulse heights of scintillation pulses from fully recorded digital waveforms. Characterization studies and settings optimization are carried out in monoenergetic neutron fields at the Physikalisch-Technische Bundesanstalt (PTB) ion accelerator facility (PIAF), in order to obtain the angle-dependent fluence response of SciFi to DD and DT neutrons. Measurements performed in deuterium plasmas of the tokamak ASDEX Upgrade (AUG) and the stellarator-heliotron Large Helical Device (LHD) provide a proof of principle of SciFi's capability to study triton burn-up time-dependently, since both DD and DT neutron count rates in SciFi qualitatively match model predictions.From these measurements as well as from models of triton burn-up in future deuterium plasmas of W7-X it is concluded that SciFi will also provide sufficient temporal resolution in the range of the slowing-down time of DD fusion-born tritons in high performance plasmas of W7-X, in which DT neutron rates exceed a value of 1e12 per s. This value is exceeded for a modeled neutral beam injection (NBI) heating scenario of W7-X and a thermonuclear scenario, which uses observed density and temperature profiles from a W7-X hydrogen plasma exclusively heated by electron cyclotron resonance heating. The DT neutron rates and triton burn-up ratios in the range of per mille to about one percent are in the same order of magnitude as observed in NBI heated deuterium plasmas of other medium sized fusion devices such as AUG and LHD.The spatial resolution of SciFi will not be sufficient for a profile measurement and in lower performance plasmas SciFi will only yield a discharge integrated triton burn-up measurement. On the one hand, another absolutely calibrated neutron diagnostic (in NBI heated operation at least a fission chamber calibrated for DD and DT neutrons) like a neutron activation system is required for cross-calibration and quantitative triton burn-up studies with SciFi. On the other hand, SciFi might be used to cross-validate other neutron and fast-ion diagnostics, especially in high performance plasmas with high neutron rates, due to the large dynamic range of SciFi, thus high count rate capabilitiesFurther Monte Carlo modeling, especially of the SciFi detector itself and the neutron propagation at W7-X, is proposed to enhance a quantitative forward model and test whether different detector positions or a detector with more scintillation fibers improve SciFi's physics capabilities significantly.
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•Modelling in preparation for future deuterium campaign.•The goal is to study tritium burn-up.•Modelling restricted to high energy neutrons.•Model for assessing Scintillating Fibre ...neutron detector diagnostics.•Detailed CAD based geometry based on unstructured mesh.
In this work, a Serpent 2 neutronics model of the Wendelstein 7-X (W7-X) stellarator is prepared, and an response function for the Scintillating-Fibre neutron detector (SciFi) is calculated using the model. The neutronics model includes the simplified geometry for the key components of the stellarator itself as well as the torus hall. The objective of the model is to assess the 14.1 MeV neutron flux from deuteron-triton fusions in W7-X, where the neutrons are modelled only until they have slowed down to 1 MeV energy. The key messages of this article are: demonstration of unstructured mesh geometry usage for stellarators, W7-X in particular; technical documentation of the model and first insights in fast neutron behaviour in W7-X, especially related to the SciFi: the model indicates that the superconducting coils are the strongest scatterers and block neutrons from large parts of the plasma. The back-scattering from e.g. massive steel support structures is found to be small. The SciFi will detect neutrons from an extended plasma volume in contrast to having an effective line-of-sight.
Neutron production rates in fusion devices are determined not only by the kinetic profiles but also the fast ion slowing-down distributions. In this work, we investigate the effect of magnetic ...configuration on neutron production rates in future deuterium plasmas in the Wendelstein 7-X (W7-X) stellarator. The neutral beam injection, beam and triton slowing-down distributions, and the fusion reactivity are simulated with the ASCOT suite of codes. The results indicate that the magnetic configuration has only a small effect on the production of 2.45 MeV neutrons from thermonuclear and beam-target fusion. The 14.1 MeV neutron production rates were found to be between \(1.49 \times 10^{12}\) \(\mathrm{s}^{-1}\) and \(1.67 \times 10^{12}\) \(\mathrm{s}^{-1}\), which is estimated to be sufficient for a time-resolved detection using a scintillating fiber detector, although only in high-performance discharges.
In this work, a Serpent 2 neutronics model of the Wendelstein 7-X (W7-X) stellarator is prepared, and an response function for the Scintillating-Fibre neutron detector (SciFi) is calculated using the ...model. The neutronics model includes the simplified geometry for the key components of the stellarator itself as well as the torus hall. The objective of the model is to assess the 14.1 MeV neutron flux from deuteron-triton fusions in W7-X, where the neutrons are modelled only until they have slowed down to 1 MeV energy. The key messages of this article are: demonstration of unstructured mesh geometry usage for stellarators, W7-X in particular; technical documentation of the model and first insights in fast neutron behaviour in W7-X, especially related to the SciFi: the model indicates that the superconducting coils are the strongest scatterers and block neutrons from large parts of the plasma. The back-scattering from e.g. massive steel support structures is found to be small. The SciFi will detect neutrons from an extended plasma volume in contrast to having an effective line-of-sight.