8.1 Power Load
137
Fig. 8.4 Radiation versus
density at the end of the
burn-through phase in JET
(Reprinted with permission
from [13])
(b) fuel recycling and retention, (c) impurity concentration and radiation have been
studied and compared between JET-C and JET-ILW. It is revealed that the influence
of PFM on plasm performance is quite large. Brezinsek et al. [16] have summarized
main observations as follows:
(a) In the H-mode plasmas for JET-ILW, primary erosion source is low and the
material migration from the main chamber to the divertor is lowered by a factor
of 7 and that from plasma facing to remote areas within the divertor by a factor
of 30–50. The energetic threshold for Be sputtering minimizes the primary
erosion source and inhibits multi-step re-erosion in the divertor. The physical
sputtering yield of W by Be ions is as low as 10
−5 .
(b) The long-term fuel retention in JET-ILW is reduced by factor 10–20 compared
with that in JET C-wall. The remaining retention is caused by implantation and
co-deposition with beryllium and residual impurities. Outgassing has gained
importance and impacts on the recycling properties of beryllium and tungsten
(Hydrogen retention is discussed in Sect. 8.4).
(c) The low effective plasma charge (Z eff = 1 ~ 2) and low radiation capability
of beryllium reveal the bare deuterium plasma physics. Moderate nitrogen
seeding, reaching Z eff = 1.6, restores in particular the confinement and the LH threshold behavior. ITER compatible divertor conditions with stable semidetachment were obtained owing to a higher density limit with ILW. Overall
JET demonstrated successful plasma operation in the Be/W material combination and confirms its advantageous PMI behavior and gives strong support
to the ITER material selection.
137
Fig. 8.4 Radiation versus
density at the end of the
burn-through phase in JET
(Reprinted with permission
from [13])
(b) fuel recycling and retention, (c) impurity concentration and radiation have been
studied and compared between JET-C and JET-ILW. It is revealed that the influence
of PFM on plasm performance is quite large. Brezinsek et al. [16] have summarized
main observations as follows:
(a) In the H-mode plasmas for JET-ILW, primary erosion source is low and the
material migration from the main chamber to the divertor is lowered by a factor
of 7 and that from plasma facing to remote areas within the divertor by a factor
of 30–50. The energetic threshold for Be sputtering minimizes the primary
erosion source and inhibits multi-step re-erosion in the divertor. The physical
sputtering yield of W by Be ions is as low as 10
−5 .
(b) The long-term fuel retention in JET-ILW is reduced by factor 10–20 compared
with that in JET C-wall. The remaining retention is caused by implantation and
co-deposition with beryllium and residual impurities. Outgassing has gained
importance and impacts on the recycling properties of beryllium and tungsten
(Hydrogen retention is discussed in Sect. 8.4).
(c) The low effective plasma charge (Z eff = 1 ~ 2) and low radiation capability
of beryllium reveal the bare deuterium plasma physics. Moderate nitrogen
seeding, reaching Z eff = 1.6, restores in particular the confinement and the LH threshold behavior. ITER compatible divertor conditions with stable semidetachment were obtained owing to a higher density limit with ILW. Overall
JET demonstrated successful plasma operation in the Be/W material combination and confirms its advantageous PMI behavior and gives strong support
to the ITER material selection.