One of the scenarios actively studied during the 2003 trace tritium experimental
campaign performed on JET includes a gas puff of small amounts of tritium into
sawtooth-unstable H-mode plasmas heated by deuterium beams. The sawtooth
crashes observed in these discharges, with the electron cyclotron emission
diagnostics, are frequently accompanied by the oscillations of the 14MeV
neutron emission, produced mainly due to the reaction between the deuterium
beam and the thermal tritium. Such oscillations are clearly seen in low density
plasmas while they are weak or absent at high density. The goal of this work
is to explain the different behaviour of the oscillations of neutron emission
with density. For this purpose, the dynamics of the trace tritium and beam
deuterium during the sawtooth crash in discharges with different plasma density
is studied numerically using the TRANSP code. In addition, a possibility of
using the neutron measurements in sawtoothing low density plasmas for the
test of the full and partial reconnection models is discussed and the sensitivity
of the simulations to the key parameters of these models is presented.
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