could be used to induce the lithium flow [124] allowing to avoid lithium overheating
by the plasma that results in the excessive lithium influx into the plasma. However,
large uncontrolled plasma currents during ELMs can splash the freely flowing
lithium into the plasma, which can terminate the discharge. An alternative way of
introducing lithium for the PFM is to use some porous structure, so that lithium
would wet up the front surface of this structure but would still be confined in the
pores [118, 119]. Virtually all the available experimental data from current tokamaks
using, in some way, lithium report a significant reduction of plasma contamination
with impurity and improvement of core plasma confinement. However, lithium is a
strong absorber of the hydrogen isotopes. Therefore, to maintain the tritium budget,
the application of lithium in future reactors would require virtually complete tritium
recovery from lithium. However, on the other hand, strong absorption of hydrogen
can, potentially, open the way to a new, very favorable “zero-recycling” operational
regime of a tokamak [125]. Recent experimental data seem to show that such a
regime could indeed exist [121].
3.3 Conclusions
In conclusion to this chapter, it would be fair to say that the situation with the
plasma-material interactions and material-related effects is far from being satisfactory and much more should be done in this area. Whereas we understand rather well
the basic features of particle reflection from the material targets and physical
Fig. 3.12 Temporal variation of (a) number of plasma particles, (b) dynamic wall retention, (c)
neutral pressure in the sub-divertor region, and (d) cumulative wall retention, in a JET discharge.
(Reproduced with permission from [116], © Elsevier 2013)
3.3 Conclusions
65
by the plasma that results in the excessive lithium influx into the plasma. However,
large uncontrolled plasma currents during ELMs can splash the freely flowing
lithium into the plasma, which can terminate the discharge. An alternative way of
introducing lithium for the PFM is to use some porous structure, so that lithium
would wet up the front surface of this structure but would still be confined in the
pores [118, 119]. Virtually all the available experimental data from current tokamaks
using, in some way, lithium report a significant reduction of plasma contamination
with impurity and improvement of core plasma confinement. However, lithium is a
strong absorber of the hydrogen isotopes. Therefore, to maintain the tritium budget,
the application of lithium in future reactors would require virtually complete tritium
recovery from lithium. However, on the other hand, strong absorption of hydrogen
can, potentially, open the way to a new, very favorable “zero-recycling” operational
regime of a tokamak [125]. Recent experimental data seem to show that such a
regime could indeed exist [121].
3.3 Conclusions
In conclusion to this chapter, it would be fair to say that the situation with the
plasma-material interactions and material-related effects is far from being satisfactory and much more should be done in this area. Whereas we understand rather well
the basic features of particle reflection from the material targets and physical
Fig. 3.12 Temporal variation of (a) number of plasma particles, (b) dynamic wall retention, (c)
neutral pressure in the sub-divertor region, and (d) cumulative wall retention, in a JET discharge.
(Reproduced with permission from [116], © Elsevier 2013)
3.3 Conclusions
65