JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
reaction 6 Li + t 8 Li*[0.981] + p – 0.18MeV ; 8 Li* 8 Li [gr. st.] + γ which proceeds through the
excited nucleus 8 Li* emitting 0.981-MeV γ-quanta in its decay to the ground state.
As is shown in , the cross section has very
strong energy dependence at sub-MeV energy range.
This process is forbidden below the threshold at 181
keV, essentially suppressed at thermal energies, and
thus it is induced in plasma predominantly by fast
nuclei.
One more important feature is that the excited
state of 8 Li* has a short life time of 12fs, so one can
consider that 8 Li* emits γ-rays before slowing-down.
Therefore, the broadening of the 0.981-MeV γ- line
correlates strongly with the 8 decay to the ground state.
Li* emission spectrum
Fig. 1. The cross section of
which in turn might be solely governed by energetic
triton populations.
Experimental data are available at center-of-mass energies above 2 MeV [8] only. So, in Ref. [9] the
cross sections below 2 MeV were calculated within a realistic nuclear model.
6 Li(t,p1) 8 Li * as a
function of energy in the CM frame.
Energetic particle populations in the plasma are described by the Fokker-Planck equation with an
appropriate source term. We solve the Fokker-Planck equation for the populations of fusion-born
α-particles, beam-injected deuterons, and also for α knock-on, D-beam knock-on, DD burn-up tritons.
show the energetic triton populations calculated under the conditions typical of ITER. For
completeness, the Maxwellian thermal triton population ftht is also shown. We can see, the α knock-on
tritons ritons populate up to 3- to 4-MeV energy, and is
dominant ominant throughout the suprathermal energy range.
Fig. 3. Distribution of knock-on tritons, f
Fig. 2. Energy distribution functions of knock-on, D-beam
akt, in the case
of T = 20 keV (dotted line), and slope distribution
knock-on and DD burn-up tritons fakt, fbkt and fDDt.
function, fslp, with Teff = 593 keV (solid line).
The distribution function of α knock-on tritons fakt can be well fitted to a slope distribution
function defined by
neff
Et
EC
f
slp E exp , (1)
T
eff
Teff
where Teff and neff are the effective temperature and concentrations of the α knock-on tritons, respectively,
and EC is a critical energy above which fakt > ftht . Although neff is not the ‘real’ density of the α knock-on
tritons, it conveniently indicates the amplitude of fakt. For example, fakt in Fig. 2 agrees the amplitude of