TY - JOUR
T1 - Beryllium migration in JET ITER-like wall plasmas
AU - Brezinsek, S.
AU - Widdowson, A.
AU - Mayer, M.
AU - Philipps, V.
AU - Baron-Wiechec, P
AU - Coenen, J.W.
AU - Heinola, K.
AU - Huber, A.
AU - Likonen, Jari
AU - Petersson, P.
AU - Rubel, M.
AU - Stamp, M.F.
AU - Borodin, D.
AU - Coad, J.P.
AU - Carrasco, A.G.
AU - Kirschner, A.
AU - Krat, S.
AU - Krieger, K.
AU - Lipschultz, B.
AU - Linsmeier, Ch.
AU - Matthews, G.F.
AU - Schmid, K.
AU - JET Contributors
N1 - Project code: 104445
PY - 2015
Y1 - 2015
N2 - JET is used as a test bed for ITER, to investigate
beryllium migration which connects the lifetime of
first-wall components under erosion with tokamak safety,
in relation to long-term fuel retention. The (i) limiter
and the (ii) divertor configurations have been studied in
JET-ILW (JET with a Be first wall and W divertor), and
compared with those for the former JET-C (JET with
carbon-based plasma-facing components (PFCs)). (i) For
the limiter configuration, the Be gross erosion at the
contact point was determined in situ by spectroscopy as
between 4% (Ein = 35 eV) and more than 100%, caused by Be
self-sputtering (Ein = 200 eV). Chemically assisted
physical sputtering via BeD release has been identified
to contribute to the effective Be sputtering yield, i.e.
at Ein = 75 eV, erosion was enhanced by about 1/3 with
respect to the bare physical sputtering case. An
effective gross yield of 10% is on average representative
for limiter plasma conditions, whereas a factor of 2
difference between the gross erosion and net erosion,
determined by post-mortem analysis, was found. The
primary impurity source in the limiter configuration in
JET-ILW is only 25% higher (in weight) than that for the
JET-C case. The main fraction of eroded Be stays within
the main chamber. (ii) For the divertor configuration,
neutral Be and BeD from physically and chemically
assisted physical sputtering by charge exchange neutrals
and residual ion flux at the recessed wall enter the
plasma, ionize and are transported by scrape-off layer
flows towards the inner divertor where significant net
deposition takes place. The amount of Be eroded at the
first wall (21 g) and the Be amount deposited in the
inner divertor (28 g) are in fair agreement, though the
balancing is as yet incomplete due to the limited
analysis of PFCs. The primary impurity source in the
JET-ILW is a factor of 5.3 less in comparison with that
for JET-C, resulting in lower divertor material
deposition, by more than one order of magnitude. Within
the divertor, Be performs far fewer re-erosion and
transport steps than C due to an energetic threshold for
Be sputtering, and inhibits as a result of this the
transport to the divertor floor and the pump duct
entrance. The target plates in the JET-ILW inner divertor
represent at the strike line a permanent net erosion
zone, in contrast to the net deposition zone in JET-C
with thick carbon deposits on the CFC (carbon-fibre
composite) plates. The Be migration identified is
consistent with the observed low long-term fuel retention
and dust production with the JET-ILW.
AB - JET is used as a test bed for ITER, to investigate
beryllium migration which connects the lifetime of
first-wall components under erosion with tokamak safety,
in relation to long-term fuel retention. The (i) limiter
and the (ii) divertor configurations have been studied in
JET-ILW (JET with a Be first wall and W divertor), and
compared with those for the former JET-C (JET with
carbon-based plasma-facing components (PFCs)). (i) For
the limiter configuration, the Be gross erosion at the
contact point was determined in situ by spectroscopy as
between 4% (Ein = 35 eV) and more than 100%, caused by Be
self-sputtering (Ein = 200 eV). Chemically assisted
physical sputtering via BeD release has been identified
to contribute to the effective Be sputtering yield, i.e.
at Ein = 75 eV, erosion was enhanced by about 1/3 with
respect to the bare physical sputtering case. An
effective gross yield of 10% is on average representative
for limiter plasma conditions, whereas a factor of 2
difference between the gross erosion and net erosion,
determined by post-mortem analysis, was found. The
primary impurity source in the limiter configuration in
JET-ILW is only 25% higher (in weight) than that for the
JET-C case. The main fraction of eroded Be stays within
the main chamber. (ii) For the divertor configuration,
neutral Be and BeD from physically and chemically
assisted physical sputtering by charge exchange neutrals
and residual ion flux at the recessed wall enter the
plasma, ionize and are transported by scrape-off layer
flows towards the inner divertor where significant net
deposition takes place. The amount of Be eroded at the
first wall (21 g) and the Be amount deposited in the
inner divertor (28 g) are in fair agreement, though the
balancing is as yet incomplete due to the limited
analysis of PFCs. The primary impurity source in the
JET-ILW is a factor of 5.3 less in comparison with that
for JET-C, resulting in lower divertor material
deposition, by more than one order of magnitude. Within
the divertor, Be performs far fewer re-erosion and
transport steps than C due to an energetic threshold for
Be sputtering, and inhibits as a result of this the
transport to the divertor floor and the pump duct
entrance. The target plates in the JET-ILW inner divertor
represent at the strike line a permanent net erosion
zone, in contrast to the net deposition zone in JET-C
with thick carbon deposits on the CFC (carbon-fibre
composite) plates. The Be migration identified is
consistent with the observed low long-term fuel retention
and dust production with the JET-ILW.
U2 - 10.1088/0029-5515/55/6/063021
DO - 10.1088/0029-5515/55/6/063021
M3 - Article
SN - 0029-5515
VL - 55
JO - Nuclear Fusion
JF - Nuclear Fusion
IS - 6
M1 - 063021
ER -
