Neutron wall emission in tokamaks and plasma diagnostics

Antozzi, P; Gorini, G.; Källne, J.; Ramström, E.

doi:10.1016/0168-9002(95)00712-1

Cited by 10 publications

(10 citation statements)

References 10 publications

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“…[1][2][3][4][5][6] In plasmas of mixed deuterium and tritium fuel, the following neutron-producing reactions are possible ͑energies in MeV are given͒: D + D → 3 He͑0.820͒ + n͑2.449͒, ͑1͒ Previous work has shown that neutron emission spectroscopy ͑NES͒ is potentially capable of contributing to this measurement.…”

Section: Introductionmentioning

confidence: 99%

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Ericsson

Conroy

Johnson

et al. 2010

Review of Scientific Instruments

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The determination of the fuel ion ratio n(t)/n(d) in ITER is required at a precision of 20%, time resolution of 100 ms, spatial resolution of a/10, and over a range of 0.016 keV and for n(T)/n(D)<0.6. A crucial issue is the signal-to-background situation in the measurement of the weak 2.5 MeV emission from DD reactions in the presence of a background of scattered 14 MeV DT neutrons. Important experimental input and corroboration for this assessment are presented from the time-of-flight neutron spectrometer at JET where the presence of a strong component of backscattered neutrons is observed. Neutron emission components on ITER due to beam-thermal and tritium-tritium reactions can further enhance the prospects for NES.

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Section: Introductionmentioning

confidence: 99%

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Ericsson

Conroy

Johnson

et al. 2010

Review of Scientific Instruments

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“…Synthetic data studies on ITER have suggested that the fuel ratio with an MPR system can operate up to n T /n D = 60% [39], assuming a near radial view of the plasma. A tangential view is expected to provide a higher possible fuel ratio measurement by at least a factor of 3 [53,54]. However, this is not observed in the MCNP6 simulations performed for MQ1.…”

Section: Fuel Ion Ratiomentioning

confidence: 94%

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

Tinguely

Rosenthal

Simpson

et al. 2019

Fusion Engineering and Design

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Advancements in high temperature superconducting technology have opened a path toward high-field, compact fusion devices. This new parameter space introduces both opportunities and challenges for diagnosis of the plasma. This paper presents a physics review of a neutron diagnostic suite for a SPARC-like tokamak [Greenwald et al 2018 doi:10.7910/DVN/OYYBNU]. A notional neutronics model was constructed using plasma parameters from a conceptual device, called the MQ1 (Mission Q ≥ 1) tokamak. The suite includes time-resolved micro-fission chamber (MFC) neutron flux monitors, energy-resolved radial and tangential magnetic proton recoil (MPR) neutron spectrometers, and a neutron camera system (radial and off-vertical) for spatially-resolved measurements of neutron emissivity. Geometries of the tokamak, neutron source, and diagnostics were modeled in the Monte Carlo N-Particle transport code MCNP6 to simulate expected signal and background levels of particle fluxes and energy spectra. From these, measurements of fusion power, neutron flux and fluence are feasible by the MFCs, and the number of independent measurements required for 95% confidence of a fusion gain Q ≥ 1 is assessed. The MPR spectrometer is found to consistently overpredict the ion temperature and also have a 1000× improved detection of alpha knock-on neutrons compared to previous experiments. The deuterium-tritium fuel density ratio, however, is measurable in this setup only for trace levels of tritium, with an upper limit of n T /n D ≈ 6%, motivating further diagnostic exploration. Finally, modeling suggests that in order to adequately measure the self-heating profile, the neutron camera system will require energy and pulse-shape discrimination to suppress otherwise overwhelming fluxes of low energy neutrons and gamma radiation.

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“…Scattered and direct neutron simulations for the plasma focus device PF-1000 are described in [8], where it is shown that accurate analysis of collected neutron spectra would require scattered neutrons to be taken into account. In [9], the authors anticipate that the advent of more advanced neutron spectrometers will make the scattered flux a limiting factor in the accuracy of neutron spectral analysis. With the installation of the TOFOR neutron spectrometer [10] at JET, this prediction was realized.…”

Section: Introductionmentioning

confidence: 99%

“…In [9], Antozzi et al report on a thorough study of the expected scattered neutron flux from 14 MeV neutrons in a large tokamak using MCNP simulations. Scatter on carbon and iron nuclei is investigated independently and the scattered flux is analysed in terms of contributions from single scattering, inboard and outboard multiple scattering.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we take the practical approach of focusing on what the scattered neutron spectrum as detected with TOFOR should look like according to simulations, how sensitive it is to parameter variations and how it can be accounted for in the analysis of measured data. MCNPX 2.5 [12] is used in the simulations and the results are compared with [9] when relevant to verify consistency. We will show how the correction for the scattered neutron flux can be done in the analysis of TOFOR data in the general case of applied auxiliary heating and rather complex neutron spectra without prior knowledge of the 'temperature' (or equivalent spectral shape) by creating a matrix of expected scatter spectra as a function of direct neutron energy, folding this with an approximation of the direct spectrum from the data and iterating until a scatter component of the correct shape is produced.…”

Section: Introductionmentioning

confidence: 99%

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Modelling and TOFOR measurements of scattered neutrons at JET

Johnson

Conroy

Cecconello

et al. 2010

Plasma Phys. Control. Fusion

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In this paper, the scattered and direct neutron fluxes in the line of sight (LOS) of the TOFOR neutron spectrometer at JET are simulated and the simulations compared with measurement results. The Monte Carlo code MCNPX is used in the simulations, with a vessel material composition obtained from the JET drawing office and neutron emission profiles calculated from TRANSP simulations of beam ion density profiles. The MCNPX simulations show that the material composition of the scattering wall has a large effect on the shape of the scattered neutron spectrum. Neutron source profile shapes as well as radial and vertical source displacements in the TOFOR LOS are shown to only marginally affect the scatter, while having a larger impact on the direct neutron flux. A matrix of simulated scatter spectra for mono-energetic source neutrons is created which is folded with an approximation of the source spectrum for each JET pulse studied to obtain a scatter component for use in the data analysis. The scatter components thus obtained are shown to describe the measured data. It is also demonstrated that the scattered flux is approximately constant relative to the total neutron yield as measured with the JET fission chambers, while there is a larger spread in the direct flux, consistent with simulations. The simulated effect on the integrated scattered/direct ratio of an increase with movements outward along the radial direction and a drop at higher values of the vertical plasma

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Neutron wall emission in tokamaks and plasma diagnostics

Cited by 10 publications

References 10 publications

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

Modelling and TOFOR measurements of scattered neutrons at JET

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Neutron wall emission in tokamaks and plasma diagnostics

Cited by 10 publications

References 10 publications

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Neutron spectroscopy as a fuel ion ratio diagnostic: Lessons from JET and prospects for ITER

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

Modelling and TOFOR measurements of scattered neutrons at JET

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Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak