68
4 Responses of Plasma-Facing Surface to Power Load Given by Radiation …
Fig. 4.18 Reemission of He
implanted in Al at RT with
the incident energy of
20 keV and flux of 4.7 ×
10 14 cm −2 s −1 [32]
Implanted fluence ( x 10 22 m -2 )
Reemission rate (Arb. Unit)
temperatures with melting points of target materials [32]. In the temperature region
assigned as range III in Fig. 4.20 fuzz structure should appear. Because of the large
size of He atoms, its migration is like vacancy migration accompanying movements
of substrate atoms suppressing the formation of large size bubbles.
Under the surface regions where energetic He ions or other ions are injected,
various defects are formed such as interstitials, vacancies, their clusters, bubbles,
dislocation loops, and so on, which have been extensively studied as radiation
damages causing degradation of materials properties but are not discussed in this
book.
4.7 Interaction of Released Particles with Photons
and Electrons in Boundary Plasmas
Interactions of released particles from PFS with electrons and photons in boundary
plasma have been the main subject of PMI. Various phenomena appear in boundary
plasma and have been extensively studied. Interactions of C released from divertor
with boundary plasmas in carbon machines have been quite important in C-wall
tokamak and extensively studied. Figure 4.21 is a good example showing ionization
and recombination of C atom or ions with the impact of electron/photon [33]. For
the C-wall, the amount of eroded materials (C and hydrocarbon) is large. Although
most of the eroded materials from PFS are promptly deposited, as discussed above,
appreciable amounts of them enter boundary plasma and ionized as indicated in
Fig. 4.21. The ionization takes energy from boundary plasma and contributes to its
cooling. Subsequently, the ionized C captures electrons referred to as recombination,
which releases energy as radiation contributing to the cooling of the boundary plasma.
In recombination plasma with high density neutral in divertor, the power exhaust
driven by the recombination process is so powerful and dominate the PMI process,
as often observed as MARFE in JT-60U [33] and Carbon blooms in JET and TFTR
[34].
4 Responses of Plasma-Facing Surface to Power Load Given by Radiation …
Fig. 4.18 Reemission of He
implanted in Al at RT with
the incident energy of
20 keV and flux of 4.7 ×
10 14 cm −2 s −1 [32]
Implanted fluence ( x 10 22 m -2 )
Reemission rate (Arb. Unit)
temperatures with melting points of target materials [32]. In the temperature region
assigned as range III in Fig. 4.20 fuzz structure should appear. Because of the large
size of He atoms, its migration is like vacancy migration accompanying movements
of substrate atoms suppressing the formation of large size bubbles.
Under the surface regions where energetic He ions or other ions are injected,
various defects are formed such as interstitials, vacancies, their clusters, bubbles,
dislocation loops, and so on, which have been extensively studied as radiation
damages causing degradation of materials properties but are not discussed in this
book.
4.7 Interaction of Released Particles with Photons
and Electrons in Boundary Plasmas
Interactions of released particles from PFS with electrons and photons in boundary
plasma have been the main subject of PMI. Various phenomena appear in boundary
plasma and have been extensively studied. Interactions of C released from divertor
with boundary plasmas in carbon machines have been quite important in C-wall
tokamak and extensively studied. Figure 4.21 is a good example showing ionization
and recombination of C atom or ions with the impact of electron/photon [33]. For
the C-wall, the amount of eroded materials (C and hydrocarbon) is large. Although
most of the eroded materials from PFS are promptly deposited, as discussed above,
appreciable amounts of them enter boundary plasma and ionized as indicated in
Fig. 4.21. The ionization takes energy from boundary plasma and contributes to its
cooling. Subsequently, the ionized C captures electrons referred to as recombination,
which releases energy as radiation contributing to the cooling of the boundary plasma.
In recombination plasma with high density neutral in divertor, the power exhaust
driven by the recombination process is so powerful and dominate the PMI process,
as often observed as MARFE in JT-60U [33] and Carbon blooms in JET and TFTR
[34].