Chapter 4
Responses of Plasma-Facing Surface
to Power Load Given by Radiation
and Energetic Particles
4.1 Introduction
Material surfaces exposed or facing to plasma are subjected to radiation (energetic
photons) and particles including ions, neutrals and electrons, and residual gases in
a reactor vessel. Injected photons and particles except directly reflected ones lose
their energy by collisional processes in materials until they fully lose their energy
to stop at a certain depth which changes depending on the incident energy. As the
consequence of such energetic particle injection, secondary particles and photons, in
addition to their reflection/scattering, are emitted from the surface and near surface
of the materials, and the materials are modified with injected particles remained and
various defects caused by collisional processes of the incident particles and their
constituent atoms.
Figure 4.1 schematically shows basic processes of ion solid interactions [1].
Although the driving force of electromagnetic interaction of electrons with materials
is generally the same as that of the ions, their lighter mass results in less significant
effects. Except for quite high-energy injection (>~ MeV), electrons do not displace
constituent atoms of the materials. Therefore, the influence of electron impact on
plasma-facing materials (PFM) is far less than that given by ion impact. However,
in a fusion reactor, the electron impact would have a certain role as emissions of
secondary electrons and photons.
It should be noted that depending on transferred energy in each phenomenon
in Fig. 4.1, its time duration changes, from initial ion incidence within picosecond
to nanosecond to thermalization within second to hour as shown in Fig. 4.2 (See
also Fig. 1.3). The figures also show characteristic times and transferred energies
in physical and chemical events on atomic scale. Details of the collisional process
of constituent elements of materials with injected energetic ions including neutrons
are described in various textbooks relating radiation damages like, for example,
references [2–4]. This chapter deals mainly with these phenomena relating to plasma–
material interactions (PMI), i.e. occurring on/in PFM and other components in a
reactor vessel.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
T. Tanabe, Plasma-Material Interactions in a Controlled Fusion Reactor, Springer Series
in Plasma Science and Technology, https://doi.org/10.1007/978-981-16-0328-0_4
49
Responses of Plasma-Facing Surface
to Power Load Given by Radiation
and Energetic Particles
4.1 Introduction
Material surfaces exposed or facing to plasma are subjected to radiation (energetic
photons) and particles including ions, neutrals and electrons, and residual gases in
a reactor vessel. Injected photons and particles except directly reflected ones lose
their energy by collisional processes in materials until they fully lose their energy
to stop at a certain depth which changes depending on the incident energy. As the
consequence of such energetic particle injection, secondary particles and photons, in
addition to their reflection/scattering, are emitted from the surface and near surface
of the materials, and the materials are modified with injected particles remained and
various defects caused by collisional processes of the incident particles and their
constituent atoms.
Figure 4.1 schematically shows basic processes of ion solid interactions [1].
Although the driving force of electromagnetic interaction of electrons with materials
is generally the same as that of the ions, their lighter mass results in less significant
effects. Except for quite high-energy injection (>~ MeV), electrons do not displace
constituent atoms of the materials. Therefore, the influence of electron impact on
plasma-facing materials (PFM) is far less than that given by ion impact. However,
in a fusion reactor, the electron impact would have a certain role as emissions of
secondary electrons and photons.
It should be noted that depending on transferred energy in each phenomenon
in Fig. 4.1, its time duration changes, from initial ion incidence within picosecond
to nanosecond to thermalization within second to hour as shown in Fig. 4.2 (See
also Fig. 1.3). The figures also show characteristic times and transferred energies
in physical and chemical events on atomic scale. Details of the collisional process
of constituent elements of materials with injected energetic ions including neutrons
are described in various textbooks relating radiation damages like, for example,
references [2–4]. This chapter deals mainly with these phenomena relating to plasma–
material interactions (PMI), i.e. occurring on/in PFM and other components in a
reactor vessel.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
T. Tanabe, Plasma-Material Interactions in a Controlled Fusion Reactor, Springer Series
in Plasma Science and Technology, https://doi.org/10.1007/978-981-16-0328-0_4
49