3.5 Power Load by Neutrons
45
6 Li + n → T +
4 He + 4.8MeV
7 Li + n → T +
4 He + n − 2.5MeV
The reaction products of T and
4 He have enough energy to displace constituent
atoms of the breeding materials and damages produced in the breeding materials trap
T and make thermal recovery of T harder. At the same time, γ radiation given by the
reaction (2.1) and induced by neutron activation of structure materials increases the
temperature to enhance the chemical process in the blanket system.
Although T breeding and recovery in the blanket to fulfill the fuel self-sufficiency
are key issues for the establishments of a fusion reactor as an energy source, they are
not discussed here. One can refer a book concentrating T as a fusion fuel [12].
3.6 Mitigation of Power Load (Power Exhaust)
As discussed in Sect. 3.2, the power used to sustain burning plasma should be
exhausted as radiation and particle energy and loaded to PFM. However, the power
load should be kept below the threshold of material damage. Hence, the amount of
loaded power, areal size, and time duration are limited. In steady-state operation,
the power load to the divertor area is the highest. The power load reduction has
been tried with either or both of the reduction of the particle flux and dissipation of
radiation to a wider area. To realize the former, increasing the divertor target area is
straightforward and making W-shaped divertor to have longer legs is a suitable way,
although it makes the divertor structure complex. To enhance the radiation in front of
PFM, impurity seeding is studied [4], in which an inert gas with medium atomic (Z)
number, such as N 2 , Ne, and Ar, is introduced in boundary plasma as an impurity.
High radiation from impurites used to be troublesome to reduce plasma temperature when plasma temperature was under 1 keV as depicted in Fig. 1.4. For higher
temperature plasma over 5 keV, central radiation from low Z impurities is not significant, while their radiation in boundary plasma becomes significant. In C-wall tokamaks, significant radiation from eroded C was observed as Carbon blooms in JET
and TFTR [13] and Carbon MARFE in JT-60U [14], of which details are given in
Sect. 4.7 in Chap. 4. This is a typical example showing that research targets or physics
and chemistry in plasma change with plasma temperature or with the development
of plasma confinement, as discussed in Chap. 1.
Formation of detached plasma [15] in divertor area is another way, which is
realized with an increase of gas pressure under appropriated control of pumping
speed and additional gas puffing either fuel gas or impurity gases.
The transient power load should be kept low enough to avoid the destruction of
plasma-facing components including material damages of PFM. Since disruption
would give the most severe damages, lots of effort have been done to avoid the
disruption and to mitigate the material damage [16, 17]. Still, disruption-free plasma
is not likely established in ITER and should be one of the most important research
45
6 Li + n → T +
4 He + 4.8MeV
7 Li + n → T +
4 He + n − 2.5MeV
The reaction products of T and
4 He have enough energy to displace constituent
atoms of the breeding materials and damages produced in the breeding materials trap
T and make thermal recovery of T harder. At the same time, γ radiation given by the
reaction (2.1) and induced by neutron activation of structure materials increases the
temperature to enhance the chemical process in the blanket system.
Although T breeding and recovery in the blanket to fulfill the fuel self-sufficiency
are key issues for the establishments of a fusion reactor as an energy source, they are
not discussed here. One can refer a book concentrating T as a fusion fuel [12].
3.6 Mitigation of Power Load (Power Exhaust)
As discussed in Sect. 3.2, the power used to sustain burning plasma should be
exhausted as radiation and particle energy and loaded to PFM. However, the power
load should be kept below the threshold of material damage. Hence, the amount of
loaded power, areal size, and time duration are limited. In steady-state operation,
the power load to the divertor area is the highest. The power load reduction has
been tried with either or both of the reduction of the particle flux and dissipation of
radiation to a wider area. To realize the former, increasing the divertor target area is
straightforward and making W-shaped divertor to have longer legs is a suitable way,
although it makes the divertor structure complex. To enhance the radiation in front of
PFM, impurity seeding is studied [4], in which an inert gas with medium atomic (Z)
number, such as N 2 , Ne, and Ar, is introduced in boundary plasma as an impurity.
High radiation from impurites used to be troublesome to reduce plasma temperature when plasma temperature was under 1 keV as depicted in Fig. 1.4. For higher
temperature plasma over 5 keV, central radiation from low Z impurities is not significant, while their radiation in boundary plasma becomes significant. In C-wall tokamaks, significant radiation from eroded C was observed as Carbon blooms in JET
and TFTR [13] and Carbon MARFE in JT-60U [14], of which details are given in
Sect. 4.7 in Chap. 4. This is a typical example showing that research targets or physics
and chemistry in plasma change with plasma temperature or with the development
of plasma confinement, as discussed in Chap. 1.
Formation of detached plasma [15] in divertor area is another way, which is
realized with an increase of gas pressure under appropriated control of pumping
speed and additional gas puffing either fuel gas or impurity gases.
The transient power load should be kept low enough to avoid the destruction of
plasma-facing components including material damages of PFM. Since disruption
would give the most severe damages, lots of effort have been done to avoid the
disruption and to mitigate the material damage [16, 17]. Still, disruption-free plasma
is not likely established in ITER and should be one of the most important research