7.2 Overall Fuel Flow at Steady-State Burning
117
For enhancement of radiative cooling of the burning plasma and also for disruption
mitigation, impurity seeding such as Ne and Ar will be employed [4], which should be
also exhausted. In addition, various chemical forms of hydrocarbons will be formed
from carbon if used as a plasma-facing material, and H 2 and H 2 O always remains
as residual gas in a vacuum system. Thus, the most of D and T fueled are exhausted
as a heavily contaminated gas with H, H 2 O, various hydrocarbons and inert gasses
(He, Ne, and Ar).
Some fuels are escaping from plasma and impinge into PFM and some are retained.
The recycling coefficient (r) defined as the flux ratio of incident and outgoing fuels
at PFS gives the fuel retention rate as (1-r). Neutrons are going to blanket systems
to breed T with a breeding ratio, η, defined as the ratio of the number of produced
neutrons to that of bred T atoms. The breeding ratio, which is strongly influenced by
geometrical structure, breeding materials, neutron multipliers of the blanket system,
does not likely exceed 1.2.
Hydrogen recycling coefficient, r, is not necessarily constant. It changes when
incident fluxes of the fuels and impurities (He ash, residual gases like water, and
seeded gases like Ne and Ar) and material’s temperature. Changes of energy of
incident fuel particles also force to change r. In the following sections, a little detail
of fuel (referred to as hydrogen) recycling or behavior of hydrogen particles escaping
from plasma with higher energy is described following general features of hydrogen
recycling at PFM (metals) shown in Fig. 7.2 [5]. Energetic hydrogen ions and neutrals
escaping from plasma impinge to PFS. Except directly reflected ones which are a
few tens % of the impinging flux, the hydrogen ions and neutrals are injected into
the material within a certain depth referred to as projected range (varied depending
on incident energy). Most of the injected hydrogen particles diffuse back to the front
(injected) surface to be reemitted (reemission), and remaining migrates or diffuses
H plasma
H 0
H +
H 2
H 2
H 2 O
CH 4
H 2
C-H
H +
Ionization
Plasma facing materials
Front surface
Back surface
Diffusion
Trapping
Detrapping
Reflection and reemission
Very high incident flux 10 24 /m 2 s
Difficulty of D/T control in plasma
Influence of wall temperature
increase would be very large
Permeation resulting in contamination of cooling water
Chemical reactions
produces hazardous
molecules and dusts
Fig. 7.2 Schematic diagram of fuel (Hydrogen) flow at/in PFM
117
For enhancement of radiative cooling of the burning plasma and also for disruption
mitigation, impurity seeding such as Ne and Ar will be employed [4], which should be
also exhausted. In addition, various chemical forms of hydrocarbons will be formed
from carbon if used as a plasma-facing material, and H 2 and H 2 O always remains
as residual gas in a vacuum system. Thus, the most of D and T fueled are exhausted
as a heavily contaminated gas with H, H 2 O, various hydrocarbons and inert gasses
(He, Ne, and Ar).
Some fuels are escaping from plasma and impinge into PFM and some are retained.
The recycling coefficient (r) defined as the flux ratio of incident and outgoing fuels
at PFS gives the fuel retention rate as (1-r). Neutrons are going to blanket systems
to breed T with a breeding ratio, η, defined as the ratio of the number of produced
neutrons to that of bred T atoms. The breeding ratio, which is strongly influenced by
geometrical structure, breeding materials, neutron multipliers of the blanket system,
does not likely exceed 1.2.
Hydrogen recycling coefficient, r, is not necessarily constant. It changes when
incident fluxes of the fuels and impurities (He ash, residual gases like water, and
seeded gases like Ne and Ar) and material’s temperature. Changes of energy of
incident fuel particles also force to change r. In the following sections, a little detail
of fuel (referred to as hydrogen) recycling or behavior of hydrogen particles escaping
from plasma with higher energy is described following general features of hydrogen
recycling at PFM (metals) shown in Fig. 7.2 [5]. Energetic hydrogen ions and neutrals
escaping from plasma impinge to PFS. Except directly reflected ones which are a
few tens % of the impinging flux, the hydrogen ions and neutrals are injected into
the material within a certain depth referred to as projected range (varied depending
on incident energy). Most of the injected hydrogen particles diffuse back to the front
(injected) surface to be reemitted (reemission), and remaining migrates or diffuses
H plasma
H 0
H +
H 2
H 2
H 2 O
CH 4
H 2
C-H
H +
Ionization
Plasma facing materials
Front surface
Back surface
Diffusion
Trapping
Detrapping
Reflection and reemission
Very high incident flux 10 24 /m 2 s
Difficulty of D/T control in plasma
Influence of wall temperature
increase would be very large
Permeation resulting in contamination of cooling water
Chemical reactions
produces hazardous
molecules and dusts
Fig. 7.2 Schematic diagram of fuel (Hydrogen) flow at/in PFM