TY - JOUR
T1 - Nitrogen transport in ASDEX Upgrade
T2 - Role of surface roughness and transport to the main wall
AU - Meisl, G.
AU - Oberkofler, M.
AU - Hakola, Antti
AU - Krieger, K.
AU - Schmid, K.
AU - Lisgo, S.W.
AU - Mayer, M.
AU - Lahtinen, Aki
AU - Drenik, A.
AU - Potzel, S.
AU - Aho-Mantila, Leena
AU - ASDEX Upgrade Team
AU - EUROfusion MST1 Team
PY - 2017/8/1
Y1 - 2017/8/1
N2 - We have studied the retention of nitrogen in surfaces with varying roughness and the transport of nitrogen from the divertor to the outer midplane in experiments at the tokamak ASDEX Upgrade. To allow for a reliable identification of nitrogen retained from the plasma exposure, 5.3 · 1021 atoms of the tracer isotope 15N were injected into the private flux region of the plasma. On polished W samples exposed to the plasma in the outer divertor, the N content peaks to both sides of the strike line with an areal density of 1.5 · 1020 15N/m2 and drops to a value of 1.0 · 1020 15N/m2 in the strike line region. In contrast, the N content of samples with a rougher surface peaks at the strike line and reaches areal densities of 3.0 · 1020 15N/m2. The N deposition at the outer limiters was measured via samples exposed on the midplane manipulator. At the limiter position the 15N areal density reaches a value of 0.2 · 1020 15N/m2, only a factor of ten smaller than the areal densities in the divertor. However, a comparison to WallDYN simulations shows that the observed N content is roughly a factor of 4 smaller than the value predicted by these simulations. Possible reasons for this discrepancy are the toroidal asymmetric main wall geometry, which currently cannot be fully included in the simulations, or an enhanced re-erosion of deposited N.
AB - We have studied the retention of nitrogen in surfaces with varying roughness and the transport of nitrogen from the divertor to the outer midplane in experiments at the tokamak ASDEX Upgrade. To allow for a reliable identification of nitrogen retained from the plasma exposure, 5.3 · 1021 atoms of the tracer isotope 15N were injected into the private flux region of the plasma. On polished W samples exposed to the plasma in the outer divertor, the N content peaks to both sides of the strike line with an areal density of 1.5 · 1020 15N/m2 and drops to a value of 1.0 · 1020 15N/m2 in the strike line region. In contrast, the N content of samples with a rougher surface peaks at the strike line and reaches areal densities of 3.0 · 1020 15N/m2. The N deposition at the outer limiters was measured via samples exposed on the midplane manipulator. At the limiter position the 15N areal density reaches a value of 0.2 · 1020 15N/m2, only a factor of ten smaller than the areal densities in the divertor. However, a comparison to WallDYN simulations shows that the observed N content is roughly a factor of 4 smaller than the value predicted by these simulations. Possible reasons for this discrepancy are the toroidal asymmetric main wall geometry, which currently cannot be fully included in the simulations, or an enhanced re-erosion of deposited N.
KW - impurity migration
KW - nitrogen
KW - roughness
KW - Tokamak
KW - WallDYN
UR - http://www.scopus.com/inward/record.url?scp=85009223179&partnerID=8YFLogxK
U2 - 10.1016/j.nme.2016.10.023
DO - 10.1016/j.nme.2016.10.023
M3 - Article
SN - 2352-1791
VL - 12
SP - 51
EP - 59
JO - Nuclear Materials and Energy
JF - Nuclear Materials and Energy
ER -
