Effects of Sawtooth Crashes on Beam Ions and Fusion Product Tritons in JET

The JET neutron emission profile monitor is used to measure the 2.5MeV and 14MeV neutron emission line-integrals before and after sawtooth crashes in high d-d neutron yield, hot-ion H-mode plasmas in the Joint European Torus (JET). Deuterium-deuterium (d-d) fusion produces 2.5MeV neutrons and 1MeV tritons (t) at nearly equal rates from its two reaction channels. A plasma current of 3MA is sufficiently high to contain most of the fusion product tritons, which have similar birth orbit gyro-radii and velocity space distributions to the 3.5MeV a-particles from d-t fusion. By examining neutron emission line-integrals and tomographically-deduced local emissivity profiles, an upper limit of 10% can be placed on the net fraction of fusion product tritons which are displaced from the plasma axis by those sawtooth crashes studied. This is a much smaller net fraction than that typically observed, 35-55%, for displaced injected neutral beam deuterium ions. A study of the response of beam-injected deuterium ions to a sawtooth crash shows that the change in their axial density depends on the pre-crash spatial width of the neutron emissivity profile. The fusion product tritons respond weakly to a crash. This is consistent with the behaviour of the analogous d-d beam-thermal neutrons when extrapolated to the corresponding emissivity spatial width. The implication of these observations is that beam ions and 3.5MeV a-particles in JET may be relatively resilient to sawtooth crashes, when the spatial width of their density is sufficiently large.
Name Size  
JETP93097 2.11 Mb