138
8 PMI in Large Tokamaks
8.1.4 Power Load by High Energy Particles Produced
by Fusion
In a D-T fusion reactor, various high energy particles are generated by D-T and
D-D reactions. Alfa particles (He with maximum energy of 3.5 MeV) and neutrons
(14.1 MeV) are generated in major D-T reactions. Additionally, T (3.5 MeV),
3 He
(0.82 eV), and neutrons (2.45 MeV) are generated in minor D-D reactions. Although
most of T and alfa particles (He and
3 He) lose their energy to heat burning plasma,
some of them escape from plasma, inject to PFS, and deposit their energy.
Using the OFMC code [17], which follows fusion-produced charged particles and
is validated with JT-60U experiments, loss of the energetic particles from the plasma
due to ripple loss of TF (toroidal field) coil and their injection to PFM was calculated
[18]. Figure 8.5 shows alpha particle deposition profiles to the wall in a 2 GW fusion
power reactor. Although, the power load to PFM caused by the energetic particles
would not be significant, the loss would cause the following issues related to PMI in
a tokamak power reactor with 2 GW thermal output.
(1) If the present allowance for the ripple loss is applied, the alpha particle flux to
PFS is expected to be as high as 2 × 10
18 m
-2 ·s
−1 with average impact energy
of 1 MeV. When the first wall is made of W, the erosion rate by the physical
sputtering of the alpha particles becomes ~20 μm per burn-year. Furthermore,
blister formation and blister erosion of metal wall are concerned.
(2) Production of energetic tritons and protons is smaller than the alpha particles
by two orders of magnitude. It must be noted that the deposition region of
them on the wall is the same as that of alpha particles. However, the tritons
would raise T inventory in PFM, because they are directly injected in PFM and
continuously piled up which is discussed in Sect. 8.4.
8.2 Erosion and Deposition
8.2.1 Carbon Wall (C-Wall)
As noted in Chap. 5 (see Fig. 5.1), erosion and deposition occur at different locations
with each other resulting in materials transport in a reactor. Generally, inner first
wall is eroded, outer first wall is eroded or deposited depending on plasma character,
out divertor is erosion dominated and inner divertor is deposition dominated. Owing
to very high-power load by radiation and particle fluxes, the temperature of PFS is
raised. In particular, the temperature rises of divertor target area (or foot prints) are
largest and appreciably influence erosion/deposition rates and thermal properties of
PFS.
Erosion/deposition properties are different between C-wall and metallic wall,
especially W-wall. Nevertheless, general pictures of material transport observed in
tokamaks with the C-wall (see Fig. 5.1) is valid in JET-ILW as discussed in the next
8 PMI in Large Tokamaks
8.1.4 Power Load by High Energy Particles Produced
by Fusion
In a D-T fusion reactor, various high energy particles are generated by D-T and
D-D reactions. Alfa particles (He with maximum energy of 3.5 MeV) and neutrons
(14.1 MeV) are generated in major D-T reactions. Additionally, T (3.5 MeV),
3 He
(0.82 eV), and neutrons (2.45 MeV) are generated in minor D-D reactions. Although
most of T and alfa particles (He and
3 He) lose their energy to heat burning plasma,
some of them escape from plasma, inject to PFS, and deposit their energy.
Using the OFMC code [17], which follows fusion-produced charged particles and
is validated with JT-60U experiments, loss of the energetic particles from the plasma
due to ripple loss of TF (toroidal field) coil and their injection to PFM was calculated
[18]. Figure 8.5 shows alpha particle deposition profiles to the wall in a 2 GW fusion
power reactor. Although, the power load to PFM caused by the energetic particles
would not be significant, the loss would cause the following issues related to PMI in
a tokamak power reactor with 2 GW thermal output.
(1) If the present allowance for the ripple loss is applied, the alpha particle flux to
PFS is expected to be as high as 2 × 10
18 m
-2 ·s
−1 with average impact energy
of 1 MeV. When the first wall is made of W, the erosion rate by the physical
sputtering of the alpha particles becomes ~20 μm per burn-year. Furthermore,
blister formation and blister erosion of metal wall are concerned.
(2) Production of energetic tritons and protons is smaller than the alpha particles
by two orders of magnitude. It must be noted that the deposition region of
them on the wall is the same as that of alpha particles. However, the tritons
would raise T inventory in PFM, because they are directly injected in PFM and
continuously piled up which is discussed in Sect. 8.4.
8.2 Erosion and Deposition
8.2.1 Carbon Wall (C-Wall)
As noted in Chap. 5 (see Fig. 5.1), erosion and deposition occur at different locations
with each other resulting in materials transport in a reactor. Generally, inner first
wall is eroded, outer first wall is eroded or deposited depending on plasma character,
out divertor is erosion dominated and inner divertor is deposition dominated. Owing
to very high-power load by radiation and particle fluxes, the temperature of PFS is
raised. In particular, the temperature rises of divertor target area (or foot prints) are
largest and appreciably influence erosion/deposition rates and thermal properties of
PFS.
Erosion/deposition properties are different between C-wall and metallic wall,
especially W-wall. Nevertheless, general pictures of material transport observed in
tokamaks with the C-wall (see Fig. 5.1) is valid in JET-ILW as discussed in the next