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Sökning: onr:"swepub:oai:DiVA.org:kth-139300" > The effect of a met...

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FältnamnIndikatorerMetadata
00006164naa a2200769 4500
001oai:DiVA.org:kth-139300
003SwePub
008140108s2013 | |||||||||||000 ||eng|
0247 a https://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1393002 URI
0247 a https://doi.org/10.1088/0741-3335/55/12/1240432 DOI
040 a (SwePub)kth
041 a engb eng
042 9 SwePub
072 7a ref2 swepub-contenttype
072 7a art2 swepub-publicationtype
1001 a Beurskens, M. N. A.4 aut
2451 0a The effect of a metal wall on confinement in JET and ASDEX Upgrade
264 c 2013-11-28
264 1b IOP Publishing,c 2013
338 a print2 rdacarrier
500 a QC 20140108
520 a In both JET and ASDEX Upgrade (AUG) the plasma energy confinement has been affected by the presence of a metal wall by the requirement of increased gas fuelling to avoid tungsten pollution of the plasma. In JET with a beryllium/tungsten wall the high triangularity baseline H-mode scenario (i.e. similar to the ITER reference scenario) has been the strongest affected and the benefit of high shaping to give good normalized confinement of H-98 similar to 1 at high Greenwald density fraction of f(GW) similar to 0.8 has not been recovered to date. In AUG with a full tungsten wall, a good normalized confinement H-98 similar to 1 could be achieved in the high triangularity baseline plasmas, albeit at elevated normalized pressure beta(N) > 2. The confinement lost with respect to the carbon devices can be largely recovered by the seeding of nitrogen in both JET and AUG. This suggests that the absence of carbon in JET and AUG with a metal wall may have affected the achievable confinement. Three mechanisms have been tested that could explain the effect of carbon or nitrogen (and the absence thereof) on the plasma confinement. First it has been seen in experiments and by means of nonlinear gyrokinetic simulations (with the GENE code), that nitrogen seeding does not significantly change the core temperature profile peaking and does not affect the critical ion temperature gradient. Secondly, the dilution of the edge ion density by the injection of nitrogen is not sufficient to explain the plasma temperature and pressure rise. For this latter mechanism to explain the confinement improvement with nitrogen seeding, strongly hollow Z(eff) profiles would be required which is not supported by experimental observations. The confinement improvement with nitrogen seeding cannot be explained with these two mechanisms. Thirdly, detailed pedestal structure analysis in JET high triangularity baseline plasmas have shown that the fuelling of either deuterium or nitrogen widens the pressure pedestal. However, in JET-ILW this only leads to a confinement benefit in the case of nitrogen seeding where, as the pedestal widens, the obtained pedestal pressure gradient is conserved. In the case of deuterium fuelling in JET-ILW the pressure gradient is strongly degraded in the fuelling scan leading to no net confinement gain due to the pedestal widening. The pedestal code EPED correctly predicts the pedestal pressure of the unseeded plasmas in JET-ILW within +/- 5%, however it does not capture the complex variation of pedestal width and gradient with fuelling and impurity seeding. Also it does not predict the observed increase of pedestal pressure by nitrogen seeding in JET-ILW. Ideal peeling ballooning MHD stability analysis shows that the widening of the pedestal leads to a down shift of the marginal stability boundary by only 10-20%. However, the variations in the pressure gradient observed in the JET-ILW fuelling experiment is much larger and spans a factor of more than two. As a result the experimental points move from deeply unstable to deeply stable on the stability diagram in a deuterium fuelling scan. In AUG-W nitrogen seeded plasmas, a widening of the pedestal has also been observed, consistent with the JET observations. The absence of carbon can thus affect the pedestal structure, and mainly the achieved pedestal gradient, which can be recovered by seeding nitrogen. The underlying physics mechanism is still under investigation and requires further understanding of the role of impurities on the pedestal stability and pedestal structure formation.
650 7a NATURVETENSKAPx Fysikx Annan fysik0 (SwePub)103992 hsv//swe
650 7a NATURAL SCIENCESx Physical Sciencesx Other Physics Topics0 (SwePub)103992 hsv//eng
653 a Carbon
653 a Deuterium
653 a Experiments
653 a Fueling
653 a Impurities
653 a Nitrogen
653 a Plasma simulation
653 a Pressure gradient
653 a Recovery
653 a Tungsten
7001 a Schweinzer, J.4 aut
7001 a Angioni, C.4 aut
7001 a Burckhart, A.4 aut
7001 a Challis, C. D.4 aut
7001 a Chapman, I.4 aut
7001 a Fischer, R.4 aut
7001 a Flanagan, J.4 aut
7001 a Frassinetti, Lorenzou KTH,Fusionsplasmafysik,Association EURATOM-VR4 aut0 (Swepub:kth)u1sfgalb
7001 a Giroud, C.4 aut
7001 a Hobirk, J.4 aut
7001 a Joffrin, E.4 aut
7001 a Kallenbach, A.4 aut
7001 a Kempenaars, M.4 aut
7001 a Leyland, M.4 aut
7001 a Lomas, P.4 aut
7001 a Maddison, G.4 aut
7001 a Maslov, M.4 aut
7001 a McDermott, R.4 aut
7001 a Neu, R.4 aut
7001 a Nunes, I.4 aut
7001 a Osborne, T.4 aut
7001 a Ryter, F.4 aut
7001 a Saarelma, S.4 aut
7001 a Schneider, P. A.4 aut
7001 a Snyder, P.4 aut
7001 a Tardini, G.4 aut
7001 a Viezzer, E.4 aut
7001 a Wolfrum, E.4 aut
7102 a KTHb Fusionsplasmafysik4 org
7730 t Plasma Physics and Controlled Fusiond : IOP Publishingg 55:12, s. 124043-q 55:12<124043-x 0741-3335x 1361-6587
8564 u https://pure.mpg.de/pubman/item/item_2145496_1/component/file_2145495/Beurskens_Effect.pdf
8564 8u https://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-139300
8564 8u https://doi.org/10.1088/0741-3335/55/12/124043

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