| 1. |
- Cecconello, Marco, et al.
(författare)
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Study of the effect of sawteeth on fast ions and neutron emission in MAST using a neutron camera
- 2018
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 60:5
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the sawtooth instability on the confinement of fast ions on MAST, and the impact it has on the neutron emission, has been studied in detail using the TRANSP/NUBEAM codes coupled to a full orbit following code. The sawtooth models in TRANSP/NUBEAM indicate that, on MAST, passing and trapped fast ions are redistributed in approximately equal number and on a level that is consistent with the observations. It has not been possible to discriminate between the different sawtooth models since their predictions are all compatible with the neutron camera observations. Full orbit calculations of the fast ion motion have been used to estimate the characteristic time scales and energy thresholds that according to theoretical predictions govern the fast ions redistribution: no energy threshold for the redistribution for either passing and trapped fast ions was found. The characteristic times have, however, frequencies that are comparable with the frequencies of a m = 1, n = 1 perturbation and its harmonics with toroidal mode numbers n = 2, ..., 4, suggesting that on spherical tokamaks, in addition to the classical sawtooth-induced transport mechanisms of fast ions by attachment to the evolving perturbation and the associated E x B drift, a resonance mechanism between the m = 1 perturbation and the fast ions orbits might be at play.
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| 2. |
- Cecconello, Marco, et al.
(författare)
-
The neutron camera upgrade for MAST Upgrade
- 2018
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
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Tidskriftsartikel (refereegranskat)abstract
- The Neutron Camera Upgrade (NCU) is a neutron flux monitor consisting of six lines of sight (LoSs) under installation on Mega Ampere Spherical Tokamak (MAST) Upgrade. The NCU is expected to contribute to the study of the confinement of fast ions and on the efficiency of non-inductive current drive in the presence of on-axis and off-axis neutral beam injection by measuring the neutron emissivity profile along the equatorial plane. This paper discusses the NCU main design criteria, the engineering and interfacing issues, and the solutions adopted. In addition, the results from the characterization and performance studies of the neutron detectors using standard gamma-rays sources and a Cf-252 source are discussed. The proposed design has a time resolution of 1 ms with a statistical uncertainty of less than 10% for all MAST Upgrade scenarios with a spatial resolution of 10 cm: higher spatial resolution is possible by moving the LoSs in-between plasma discharges. The energy resolution of the neutron detector is better than 10% for a light output of 0.8 MeVee, and the measured pulse shape discrimination is satisfactory.
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