|Title||Observations on the W-transport in the core plasma of JET and ASDEX Upgrade|
|Publication Type||Journal Article|
|Year of Publication||2013|
|Authors||T. Putterich, R. Dux, R. Neu, M. Bernert, M.NA Beurskens, V. Bobkov, S. Brezinsek, C. Challis, J.W Coenen, I. Coffey, A. Czarnecka, C. Giroud, P. Jacquet, E. Joffrin, A. Kallenbach, M. Lehnen, E. Lerche, E. de la Luna, S. Marsen, G. Matthews, M-L Mayoral, R.M McDermott, A. Meigs, J. Mlynar, M. Sertoli, G.J van Rooij, ASDEX Upgrade Team, JET-EFDA Contributors|
|Journal||Plasma Physics and Controlled Fusion|
The W-transport in the core plasma of JET is investigated experimentally by deriving the W-concentration profiles from the modelling of the signals of the soft x-ray cameras. For the case of pure neutral beam heating W accumulates in the core ( r / a < 0.3) approaching W-concentrations of 10 −3 in between the sawtooth crashes, which flatten the W-profile to a concentration of about 3 × 10 −5 . When central Ion cyclotron resonant heating is additionally applied the core W-concentration decays in phases that exhibit a changed mode activity, while also the electron temperature increases and the density profile becomes less peaked. The immediate correlation between the change of magnetohydrodymanic (MHD) and the removal of W from the plasma core supports the hypothesis that the change of the MHD activity is the underlying cause for the change of transport. Furthermore, a discharge from the ASDEX Upgrade is investigated. In this case the plasma profiles exhibit small changes only, while the most prominent change occurs in the W-content of the confined plasma caused by the reduction of the fuelling deuterium gas puff. Concomintantly, the W-concentration profiles in the core plasma r / a < 0.2 steepen up reminescent to the well-known connection between central radiation and transport during cases with strong, established W-accumulation, while in the present analysis such a causality between the two during the onset of W-accumulation could not be pinned down. Both case studies exemplify that small changes of the core parameters of a plasma my influence the W-transport in the plasma core drastically.
|Alternate Title||Plasma Phys. Control. Fusion|
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