5.3 Formation of Deposited Layers Made of Eroded Materials
83
TFTR
Deposited tile
Erode tile
Photographs
Tritium profiles
Tritium intensity
Fig. 5.7 Tritium profiles on eroded and deposited tiles used as bumper limiters in TFTR [8]. In the
deposited tile, some deposited layers were exfoliated which clearly indicated that T was mostly in
the deposited layers. On the eroded tile, T retention on the plasma-facing surface was quite small,
while its tile sides were deposited and an appreciable amount of T was retained. Higher erosion on
the tile surface gave a higher deposition on its tile sides. It is noted that the T profile of the eroded
tile shows CFC structure because T retention was different between fiber and matrix in CFC
were transferred to different ordered structure reflecting nature of layered structurer
of graphite. Once such ordered structure was made, the thermal conduction along
the parallel direction of the layers became much better than the normal direction to
porous layers and enhanced the ordering within the layers.
The microstructure of the deposited carbon (C) layers was very complex because
C takes polymorphism due to three different bonding forms, sp, sp
2 , and sp
3 . The
inclusion of hydrogen also modifies their structure. In large tokamaks, such as JT-60U
and JET, the structure of deposits is significantly different depending on the location,
i.e. directions of the coming particles to be deposited and how high the temperature
they were subjected to. The ordered structure that appeared in JT-60U (Fig. 5.8) was
graphitized and less H retention owing to temperature rise, sometimes over 1300 K.
In addition, depending on where carbon sources were or where erosion occurred and
how they were transferred, the structure of the deposited materials was modified. As
an example, the columnar structure in Fig. 5.8 was caused by the deposition with the
incident angle of 60°.
Cyclic heat load and transient heat load give thermal stress between the deposited
layers and the substrate. Correspondingly, some area of the deposited layers is exfoliated as flakes as seen in Fig. 5.7. The flakes could turn to dust often observed as
small white dots appearing during plasma discharges [10–12]. Examples of the dust
collected from JET-ITER-like wall are given in Fig. 5.9 [12]. Not only the elements
83
TFTR
Deposited tile
Erode tile
Photographs
Tritium profiles
Tritium intensity
Fig. 5.7 Tritium profiles on eroded and deposited tiles used as bumper limiters in TFTR [8]. In the
deposited tile, some deposited layers were exfoliated which clearly indicated that T was mostly in
the deposited layers. On the eroded tile, T retention on the plasma-facing surface was quite small,
while its tile sides were deposited and an appreciable amount of T was retained. Higher erosion on
the tile surface gave a higher deposition on its tile sides. It is noted that the T profile of the eroded
tile shows CFC structure because T retention was different between fiber and matrix in CFC
were transferred to different ordered structure reflecting nature of layered structurer
of graphite. Once such ordered structure was made, the thermal conduction along
the parallel direction of the layers became much better than the normal direction to
porous layers and enhanced the ordering within the layers.
The microstructure of the deposited carbon (C) layers was very complex because
C takes polymorphism due to three different bonding forms, sp, sp
2 , and sp
3 . The
inclusion of hydrogen also modifies their structure. In large tokamaks, such as JT-60U
and JET, the structure of deposits is significantly different depending on the location,
i.e. directions of the coming particles to be deposited and how high the temperature
they were subjected to. The ordered structure that appeared in JT-60U (Fig. 5.8) was
graphitized and less H retention owing to temperature rise, sometimes over 1300 K.
In addition, depending on where carbon sources were or where erosion occurred and
how they were transferred, the structure of the deposited materials was modified. As
an example, the columnar structure in Fig. 5.8 was caused by the deposition with the
incident angle of 60°.
Cyclic heat load and transient heat load give thermal stress between the deposited
layers and the substrate. Correspondingly, some area of the deposited layers is exfoliated as flakes as seen in Fig. 5.7. The flakes could turn to dust often observed as
small white dots appearing during plasma discharges [10–12]. Examples of the dust
collected from JET-ITER-like wall are given in Fig. 5.9 [12]. Not only the elements