Neutron emission from beryllium reactions in JET deuterium plasmas with 3He minority

Recent fast ion studies at JET involve ion cyclotron resonance frequency (ICRF) heating tuned to minority (3)He in cold deuterium plasmas, with beryllium evaporation in the vessel prior to the session. During the experiments, the high-resolution neutron spectrometer TOFOR was used to study the energy spectrum of emitted neutrons. Neutrons of energies up to 10MeV, not consistent with the neutron energy spectrum expected from d(d,n)(3)He reactions, were observed. In this paper, we interpret these neutrons as a first-time observation of a (9)Be((3)He, n)(11)C neutron spectrum in a tokamak plasma, a conclusion based on a consistent analysis of experimental data and Monte Carlo simulations. (9)Be(a, n)(12)C and (9)Be(p, n)(9)B reactions are also simulated for p and a fusion products from d((3)He, a) p reactions; these two-step processes are seen to contribute on a level of about 10% of the single-step process in (9)Be((3)He, n) (11)C. Contributions to the total neutron yield from the (9)Be(3He, n)(11)C reaction are found to be in the range 13 +/- 3 to 57 +/- 5%. We demonstrate how TOFOR can be used to simultaneously (i) probe the deuterium distribution, providing reliable measurements of the bulk deuterium temperature, here in the range 3.2 +/- 0.4 to 6.3 +/- 1.0 keV and (ii) provide an estimate of the beryllium concentration (in the range 0.48 +/- 0.17 to 6.4 +/- 1.7% of n(e) assuming T(3He) = 300 keV). The observation of (9)Be related neutrons is relevant in view of the upcoming installation of a beryllium-coated ITER-like wall on JET and for ITER itself. An important implication is possible neutron-induced activation of the ITER vessel during the low-activation phase with ICRF heating tuned to minority (3)He in hydrogen plasmas.