4.1 Introduction
51
Various particles including charged and noncharged particles, electrons, photons,
and even phonons are emitted from the materials’ surface subjected to energetic
photons and particles. In this chapter, following the brief introduction of the energy
loss process of injected particles in Sect. 4.2, four subjects are separately described,
which are emissions of ions and neutrals in Sect. 4.3, emission of electrons and
photons in Sect. 4.4, energy reflection in Sect. 4.5, and reemission of incident ions
in Sect. 4.6. Although the emission of phonons is always accompanied by energetic particle injection, their effects on PMI are quite small and not discussed here.
However, it should be mentioned that detection of the phonons could be used as one
of the diagnostic methods to investigate boundary plasma and hence encouraged to
make more detailed investigation in future. In Sect. 4.7, interactions of released particles from PFM with photons and electrons in boundary plasma are briefly explained
as bases of PMI [5].
In PMI studies, the main subject is to understand boundary plasmas and the
influence of plasma-facing surfaces (PFS) on them. Simulations of boundary plasma,
and erosion and deposition are well developed as various codes like B2-EIRENE [6],
ERO [7], PARASOL [8], Integrated SOL/Divertor Code [9], SOLPS-ITER [10], and
UEDGE [11]. Some of them are routinely used in designing ITER and reactors.
In some codes, erosion and deposition and recycled hydrogen are included.
However, some phenomena of PMI discussed in this book are not included, and
the behavior of recycled or reemitted hydrogen is very much simplified. Recycled
hydrogen includes various species, molecule, atoms, their excited states, and ions
with a variously different energy. Therefore, for edge simulation, fluxes and energy
distributions of these species should be included. One of the aims of this book is to
demonstrate that PMI phenomena considered form material sides are more important
than that have been considered up to now.
4.2 Energy Loss Processes of Energetic Particles Injected
in a Solid Target
Figure 4.3 schematically shows energy loss processes of energetic particle injected
in a solid in micro-scale, which are consisted of two processes. If an incident particle
is neutral and its energy is high enough to ionize itself, it is immediately ionized at
the surface. Therefore, differences in the energy loss process between neutral and
ions injections are quite small. Hereafter incident particles are assumed to be ions.
Initially, electron excitation or ionization of target atoms dominates energy loss. The
energy loss of an incident ion with energy E is inversely proportional to penetration
depth (dE/dx), which is nearly constant. Because of this constant energy loss region,
the depth dominated by the ionization is referred to as the linear energy transfer
(LET) loss region.
After penetrating in a certain depth with losing energy by the electron excitation or
ionization (LET region), nuclear collisions of the incident ions and the target atoms
51
Various particles including charged and noncharged particles, electrons, photons,
and even phonons are emitted from the materials’ surface subjected to energetic
photons and particles. In this chapter, following the brief introduction of the energy
loss process of injected particles in Sect. 4.2, four subjects are separately described,
which are emissions of ions and neutrals in Sect. 4.3, emission of electrons and
photons in Sect. 4.4, energy reflection in Sect. 4.5, and reemission of incident ions
in Sect. 4.6. Although the emission of phonons is always accompanied by energetic particle injection, their effects on PMI are quite small and not discussed here.
However, it should be mentioned that detection of the phonons could be used as one
of the diagnostic methods to investigate boundary plasma and hence encouraged to
make more detailed investigation in future. In Sect. 4.7, interactions of released particles from PFM with photons and electrons in boundary plasma are briefly explained
as bases of PMI [5].
In PMI studies, the main subject is to understand boundary plasmas and the
influence of plasma-facing surfaces (PFS) on them. Simulations of boundary plasma,
and erosion and deposition are well developed as various codes like B2-EIRENE [6],
ERO [7], PARASOL [8], Integrated SOL/Divertor Code [9], SOLPS-ITER [10], and
UEDGE [11]. Some of them are routinely used in designing ITER and reactors.
In some codes, erosion and deposition and recycled hydrogen are included.
However, some phenomena of PMI discussed in this book are not included, and
the behavior of recycled or reemitted hydrogen is very much simplified. Recycled
hydrogen includes various species, molecule, atoms, their excited states, and ions
with a variously different energy. Therefore, for edge simulation, fluxes and energy
distributions of these species should be included. One of the aims of this book is to
demonstrate that PMI phenomena considered form material sides are more important
than that have been considered up to now.
4.2 Energy Loss Processes of Energetic Particles Injected
in a Solid Target
Figure 4.3 schematically shows energy loss processes of energetic particle injected
in a solid in micro-scale, which are consisted of two processes. If an incident particle
is neutral and its energy is high enough to ionize itself, it is immediately ionized at
the surface. Therefore, differences in the energy loss process between neutral and
ions injections are quite small. Hereafter incident particles are assumed to be ions.
Initially, electron excitation or ionization of target atoms dominates energy loss. The
energy loss of an incident ion with energy E is inversely proportional to penetration
depth (dE/dx), which is nearly constant. Because of this constant energy loss region,
the depth dominated by the ionization is referred to as the linear energy transfer
(LET) loss region.
After penetrating in a certain depth with losing energy by the electron excitation or
ionization (LET region), nuclear collisions of the incident ions and the target atoms