Measurements of fusion neutron energy spectra at JET by means of time-of-flight techniques

Elevant, T.; Belle, P. van; Jarvis, O.N.; Sadler, G.

doi:10.1016/0168-9002(95)00346-0

Cited by 18 publications

(6 citation statements)

References 16 publications

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“…The neutron data, for the time intervals shown in Table 11, yield tomographic reconstructions that are very similar in form to those corresponding to gamma ray emission. This is not surprising, since the nuclear reactions that give rise to gamma ray emission also emit neutrons with energies that cover a broad range [15], as was observed clearly with a high resolution neutron spectrometer. These…”

Section: Nomentioning

confidence: 65%

Gamma ray emission profile measurements from JET ICRF-heated discharges

Jarvis¹,

Adams²,

Howarth³

et al. 1996

Nucl. Fusion

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Helium 3 minority fuel ions have been observed to be accelerated to megaelectronvolt (MeV) energies by ion cyclotron radiofrequency (ICRF) heating. These energetic ions undergo nuclear reactions with impurity 'Be and 12C ions in the plasma, and characteristic gamma radiation is emitted. For special circumstances, this gamma ray emission has been detected with a 19 channel profile monitor constructed primarily for neutron measurements. Two-dimensional (2-D) profiles of the gamma radiation emission have been derived by tomographic reconstruction; these profiles correspond to a cross-section weighted density of 3He ions having energies of 2 or more MeV. As expected for ICRF heating, the observed spatial profile of the gamma radiation shows that access by the accelerated ions to the plasma volume on the high field side of the RF resonance layer is effectively inhibited. In addition, the profile appears to demand the presence of a group of passing particles that are localized in poloidal extent and are circulating some 15 cm to the low field side of the resonance layer. Apart from the 15 cm displacement, these features are well reproduced by a model that combines a 2-D bounce averaged Fokker-Planck calculation with an orbit-following code. A unique example of a gamma ray spatial profile captured at the time of a sawtooth crash shows that the profile is relatively unaffected apart from the sudden obliteration of the passing group, for which the ions are found to possess relatively high energy, presumably gained from the RF waves through the Doppler shift effect. On the basis of these observations, an explanation is proposed for the selective expulsion of RF heated fast ions from the central region of the plasma to the outer regions.

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Section: Nomentioning

confidence: 65%

Gamma ray emission profile measurements from JET ICRF-heated discharges

Jarvis¹,

Adams²,

Howarth³

et al. 1996

Nucl. Fusion

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“…That the highest energy group of the fast deuterons should suffer appreciable pitch-angle scattering while still at their peak nuclear reactivity is unexpected and is a feature specific to hot-ion discharges. The measured neutron energy spectra (Elevant et al 1995) for such discharges do have a strongly Gaussian appearance, compatible with a nearly isotropic fast ion distribution.…”

Section: Beam-plasma Reaction Ratesmentioning

confidence: 73%

Prediction/modelling of the neutron emission from hot-ion H-mode discharges in JET

Jarvis

1997

Plasma Phys. Control. Fusion

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A simple zero-dimensional computer code has been prepared for predicting the neutron emission in the initial phase of beam-heated hot-ion H-mode discharges in the Joint European Torus (JET). It performs very well for discharges with low particle recycling up to the onset of MHD-related activity, which usually occurs within one second of commencing full power heating. It can also be used to model the entire discharge, including the termination, when fuelling of the plasma volume uniformly with cold neutrals is adopted as a first-order approximation for edge recycling effects. Specifically, given the time traces for the beam heating power, the global neutron emission, average electron density, Z eff and Dα signals, the code can satisfactorily reconstruct the core volume rotation rate, ion temperature and electron temperature for the entire duration of the discharge, and it also provides an explanation for the anomalously low burnup of d-d fusion product tritons that is sometimes observed. The code provides insight into the relative intensities of the three contributing reaction mechanisms to the total neutron emission (thermal, beam-thermal and beam-beam reactions) as an aid to interpretation of data from the various neutron diagnostics on JET, including the neutron profile monitor and the neutron spectrometers. Tritium fuelling and beam injection are also implemented, so the code can be used to extrapolate the neutron emission from existing d-d discharges to that expected from similar d-t discharges.

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“…However, because the neutron emission is so strongly peaked towards the centre, the problem is amenable to simplification. In the past (Elevant et al 1995), the adoption of a single volume element has proven reasonably successful for D-D plasma discharges. Consequently, we would expect the NEPAM two-volume calculation to be entirely adequate.…”

Section: Interpretation Of Neutron Energy Spectramentioning

confidence: 99%

Prediction/modelling of the neutron emission from JET discharges

Jarvis

Conroy

2002

Plasma Phys. Control. Fusion

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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.

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Measurements of fusion neutron energy spectra at JET by means of time-of-flight techniques

Cited by 18 publications

References 16 publications

Gamma ray emission profile measurements from JET ICRF-heated discharges

Gamma ray emission profile measurements from JET ICRF-heated discharges

Prediction/modelling of the neutron emission from hot-ion H-mode discharges in JET

Prediction/modelling of the neutron emission from JET discharges

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