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The JET Team1 (presented by P. R. Thomas)
1 see Appendix to IAEA-CN-69/OV1/2
Joint European Torus, Abingdon, Oxfordshire, United Kingdom
Abstract. The 1997 DT experiment (DTE1) at the Joint European Torus
included studies of the behaviour of alpha particles in high temperature
plasmas. Clear alpha particle heating was observed in a series of otherwise
similar 10MW hot-ion H-modes by scanning the DT mixture from 0%T to
93%T. Maxima in central temperature and energy content were obtained which
corresponded with the maximum in fusion yield. Alfvén Eigenmodes (AEs) have
been detected in JET, driven by NBI or ICRH fast ions. However, in agreement
with theory, no AE activity was observed in DT plasmas which could be
attributed to alpha particle drive, except in the afterglow of some Optimised
Shear pulses. Ion Cyclotron Emission (ICE) was detected at harmonics of the
alpha particle cyclotron frequency at the outer edge of the plasma. The ICE is
interpreted as being close to magnetoacoustic cyclotron instability, driven by
inverted alpha distributions at the plasma edge. The high-energy neutral
particle spectra showed features, which are ascribed to a mixture of alphas,
neutralised by helium-like impurities, and deuterons, born from elastic
collisions with alpha particles and neutralised by hydrogen-like
impurities. The results of all these studies are consistent with classical
alpha particle trapping and slowing-down. Future DT experiments will aim to
increase alpha particle pressure, so interactions with plasma instabilities
can be studied. The measurement of knock-on neutral triton spectra offers a
clean way to determine confined alpha densities in these future experiments.
IAEA 2001
