Chapter 10
Selection of Plasma-Facing Materials
10.1 Criteria for Selection of PFM
In a fusion reactor, the combination of very high-power load and resulting high
temperatures, high radiation levels, intense production of transmuting elements and
high thermomechanical loads requires very high-performance for plasma-facing
materials (PFM). Erosion of plasma-facing components (PFC) determines their lifetime and generates a source of impurities, which cool down and dilute the plasma,
while deposition causes T retention. The resuspension of dust could be a consequence of loss-of-coolant accidents (LOCA) and lss-of-vacuum accidents (LOVA),
and it can be dangerous because of its radioactivity, toxicity, and capability causing
a hydrogen explosion [1].
Accordingly, the selection of PFM for a fusion reactor is a crucial issue. As
described in Chap. 1, PFM in plasma apparatus has been changing with improvement
of plasma confinement, targeting higher density, and temperature for self-burning.
Now major criteria for the selection of PFM are (1) tolerance to high-power load,
(2) long lifetime including low erosion and tolerance to neutron damage, and (3)
low tritium retention. To be tolerant to the first one, high melting point, high thermal
conductivity, and high heat shock resistance are mandatory. At present, mainly W
and carbon-based materials are considered to be PFM of the reactor. Although liquid
wall using liquid metals like Li is attractive and could be alternative, significant effort
is required to realize the liquid wall with reliability.
There are opinions on pros and cons of the selection of PFM in various detailed
criteria, such as (1) low radiation in plasma or low impurity release to plasma, (2)
surface damage and material loss, (3) wall life time, (4) tritium retention and easy
recovery, (5) neutron irradiation damage including activation, (6) maintenance, and
so on. In Table 10.1, important characters relating plasma materials interactions
(PMI) are compared for three PFM candidates, C, Be (Beryllium), and W. Low Z
materials like C and Be are much better than W in the aspect of plasma contamination,
while material loss by erosion is much larger for the former than the latter. The
radiation loss by impurities in the plasma center depends on their concentration, and
© 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_10
187
Selection of Plasma-Facing Materials
10.1 Criteria for Selection of PFM
In a fusion reactor, the combination of very high-power load and resulting high
temperatures, high radiation levels, intense production of transmuting elements and
high thermomechanical loads requires very high-performance for plasma-facing
materials (PFM). Erosion of plasma-facing components (PFC) determines their lifetime and generates a source of impurities, which cool down and dilute the plasma,
while deposition causes T retention. The resuspension of dust could be a consequence of loss-of-coolant accidents (LOCA) and lss-of-vacuum accidents (LOVA),
and it can be dangerous because of its radioactivity, toxicity, and capability causing
a hydrogen explosion [1].
Accordingly, the selection of PFM for a fusion reactor is a crucial issue. As
described in Chap. 1, PFM in plasma apparatus has been changing with improvement
of plasma confinement, targeting higher density, and temperature for self-burning.
Now major criteria for the selection of PFM are (1) tolerance to high-power load,
(2) long lifetime including low erosion and tolerance to neutron damage, and (3)
low tritium retention. To be tolerant to the first one, high melting point, high thermal
conductivity, and high heat shock resistance are mandatory. At present, mainly W
and carbon-based materials are considered to be PFM of the reactor. Although liquid
wall using liquid metals like Li is attractive and could be alternative, significant effort
is required to realize the liquid wall with reliability.
There are opinions on pros and cons of the selection of PFM in various detailed
criteria, such as (1) low radiation in plasma or low impurity release to plasma, (2)
surface damage and material loss, (3) wall life time, (4) tritium retention and easy
recovery, (5) neutron irradiation damage including activation, (6) maintenance, and
so on. In Table 10.1, important characters relating plasma materials interactions
(PMI) are compared for three PFM candidates, C, Be (Beryllium), and W. Low Z
materials like C and Be are much better than W in the aspect of plasma contamination,
while material loss by erosion is much larger for the former than the latter. The
radiation loss by impurities in the plasma center depends on their concentration, and
© 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_10
187