1 - Nuclear Sciences and Applications - IAEA

258 STRACHAN et al.
- Z - 1, Steady-Slate
Triton Burnup
PEAK ELECTRON TEMPERATURE (keV)
FIG. 1. Magnitude of the burnup for the 0.8 MeV 3 He ions (steady-state value) (solid points), and for
the 1 MeV triton burnup (integrated over the plasma duration) with small observed triton losses (open
circles), and with two times larger observed triton losses (open squares). The triton data are limited
to 1.4 MA plasmas. The lines are the calculated steady-state Z = 1 values. The shaded region indicates
the magnitude of the bumup expected when transient effects and realistic deuterium depletion are
included in the calculations.
d(t,n)a and d( He,p)a fusion reactions. The principal
uncertainties relate to the absolute calibrations of the relevant
nuclear detectors and the density of deuterium In the background
plasma. The 14.7 MeV protons from the burnup of the 0.8 MeV He in
the d( He,p)a fusion reaction were detected with x3 calibration
uncertainties by surface barrier detectors at the edge of the
plasma. The 14.1 MeV neutrons from the burnup of the 1 MeV tritons
in the d(t,n)a fusion reaction were detected with 35% uncertainty
by Cu(n,2n) activation [3], which was cross-calibrated to a
collimated neutron spectrometer [4].
For steady-state Z - 1 plasmas with no orbit losses, the
burnup fraction, defined as the ratio of 14.7 MeV p or 14.1 MeV n
yield to the measured 2.5 MeV n source, is expected to depend only
upon central electron temperature [5] . In Fig. 1 is plotted the
burnup fraction for the 0.8 MeV He, which slightly exceeds the
values expected for Z - 1 and, therefore, significantly exceeds (by
2x) calculated values with realistic Ze££. This apparent excess of
0.8 MeV He ions is most likely due to the uncertainty In the
absolute calibration of the 15 MeV proton detector [6,7]. An
alternate explanation could invoke enhanced reactivity due to D He
reactions between the 0.8 MeV He ions and the energetic beam ions.
For TFTR supershots, the burnup fractions for 1 MeV tritons
are five to ten times below the Z - 1 steady-state value. These
burnup fractions are thought to be below ideal levels primarily due