The knock-on tail formations in fuel-ion velocity distribution functions by energetic alpha-particles (by the T(d,n) 4 He reaction) and protons (by the D(d,p)T and 3 He(d,p) 4 He reactions) are investigated by simultaneously solving the Boltzmann-Fokker-Planck (BFP) equations for deuteron, triton, 3 He, alpha-particle and proton in an ITER-like deuterium-tritium (DT) plasma admixed with a small amount of 3 He. As a result of the 3 He inclusion, fraction of the transferred energy from energetic ions to thermal deuterons and tritons via nuclear plus interference (NI) scattering is reduced. Owing to the NI scattering of the energetic protons by fuel-ions, the latters are knocked up to higher energies. The knocking-up effect of fuel ions is enhanced with increasing 3 He concentration. It is shown that if 3 He with relative concentration of 4.2 %, i.e. n 3He /n e = 0.042, is included in T e =20 keV, n e =9.5×10 19 m-3 plasma, the magnitude of the knock-on tail in deuteron distribution function in 300 keV~3 MeV energy range is reduced by about 15 % from the value when 3 He is not externally supplied. Such knock-on tail reduction also results in alternation of the non-Gaussian neutron emission spectrum with energies less than ~13 MeV and above ~15 MeV.
The effect of pre-plasma on core heating in cone-guiding fast ignition is evaluated by two-dimensional particle-in-cell (PIC) and Fokker–Planck (FP) simulations. If the long-scale pre-plasma exists in the cone, the generated fast electron energy becomes too high for effective core heating. As a result, the energy coupling from laser to core ηL→core is reduced by 80% compared with the case without a pre-plasma. Even for the case without a pre-plasma, ηL→core obtained in the simulation is smaller than that required for 5 keV heating in FIREX-I. In order to enhance ηL→core, we propose a new target design ‘extended double cone with short inner cone wall’ for fast electron guiding to imploded core and show sufficient improvement of heating efficiency using this new cone on the basis of PIC and FP hydro-simulations.
The standard model of big bang nucleosynthesis (BBN) relies on a nuclear reaction network
operating with thermal reactivities for Maxwellian plasma. In the primordial plasma,
however, a number of non-thermal processes triggered by energetic particles of
various origins can take place. In the present work we examine in-flight nuclear
reactions induced in the plasma by MeV protons generated in D(d, p)T and
3He(d, p)4He
fusions. We particularly focus on several low threshold endoergic processes. These are
reactions omitted in the standard network—proton-induced break-ups of loosely bound D,
7Li,
7Be nuclei—and
the 3H(p, n)3He
charge-exchange reaction important for the interconversion of
A = 3
nuclei in the early universe. It is found that the break-up processes
in the plasma take the form of Maxwellian processes at temperatures
T>70 keV, while in the lower temperature range they proceed as non-thermal reactions. It is shown that
at T<70 keV the in-flight reaction channels can enhance the break-up reactivities
by several orders of magnitude. The levels of these reactivities however
remain insufficiently high to affect BBN kinetics and change the standard
prediction of light element abundances. The abundances are found to be:
Yp = 0.2457,
D/H = 2.542 × 10−5,
3He/H = 1.004 × 10−5,
7Li/H = 4.444 × 10−10. Future steps in the study of non-thermal processes in the primordial plasma are briefly
discussed.
An effect of nuclear elastic scattering ͑NES͒ on the energy transfer to plasma ions and electrons during ͑a͒ neutral beam injection ͑NBI͒ and ͑b͒ ␣-particle heating operations is examined on the basis of the Boltzmann-Fokker-Planck ͑BFP͒ equation for a beam ion and an ␣-particle in deuterium-tritium thermonuclear plasmas. The BFP calculations show that the enhancement in the fraction of the NBI heating power deposited to ions due to NES becomes appreciable when the beam energy is larger than 1 MeV. How the NES effect is influenced by the plasma condition is discussed.
Nuclear elastic scattering is included in the analysis of ignition condition and thermal instability in pure and catalysed D-D fusion reactor plasmas. Nuclear-elastic-scattering events take place, to some extent, during the slowing-down of energetic fusion products and enhance the heating of the background ions. The inclusion of this effect relaxes the minimum of the confinement requirement for self-sustained D-D plasmas by about 15%. It enhances, however, the thermal instability of the plasma, leading to an increase in the critical temperature.
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