The 'neutron deficit' in the JET tokamak

H. Weisen, Hyun Tae Kim, J. Strachan, SM Scott, Y. Baranov, J. Buchanan, M. Fitzgerald, D. Keeling, D. B. King, L. Giacomelli, T. Koskela, M. J. Weisen, C. Giroud, M. Maslov, W. G. Core, K.-D. Zastrow, D.B. Syme, S. Popovichev, S. Conroy, I. LengarL. Snoj, P. Batistoni, M. Santala, JET Contributors

Research output: Contribution to journalArticleScientificpeer-review


The measured D-D neutron rate of neutral beam heated JET baseline and hybrid H-modes in deuterium is found to be between approximately 50% and 100% of the neutron rate expected from the TRANSP code, depending on the plasma parameters. A number of candidate explanations for the shortfall, such as fuel dilution, errors in beam penetration and effectively available beam power have been excluded. As the neutron rate in JET is dominated by beam-plasma interactions, the 'neutron deficit' may be caused by a yet unidentified form of fast particle redistribution. Modelling, which assumes fast particle transport to be responsible for the deficit, indicates that such redistribution would have to happen at time scales faster than both the slowing down time and the energy confinement time. Sawteeth and edge localised modes are found to make no significant contribution to the deficit. There is also no obvious correlation with magnetohydrodynamic activity measured using magnetic probes at the tokamak vessel walls. Modelling of fast particle orbits in the 3D fields of neoclassical tearing modes shows that realistically sized islands can only contribute a few percent to the deficit. In view of these results it appears unlikely that the neutron deficit results from a single physical process in the plasma.

Original languageEnglish
Article number076029
Pages (from-to)1-11
JournalNuclear Fusion
Issue number7
Publication statusPublished - 1 Jun 2017
MoE publication typeA1 Journal article-refereed


  • Fusion reactions
  • Monte Carlo orbit code
  • Neutron yield


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