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R. Fischer, J. Fuchs, R. McDermott, S. Rathgeber, W. Suttrop, M. Willensdorfer, E. Wolfrum, . ASDEX Upgrade Team:
"Spatiotemporal response of plasma edge density and temperature to non-axisymmetric magnetic perturbations at ASDEX Upgrade";
Plasma Physics and Controlled Fusion, 54 (2012), 1150081 - 11500812.

Non-axisymmetric magnetic perturbations (MPs) were successfully applied at ASDEX
Upgrade to substantially reduce the plasma energy loss and peak divertor power load that
occur concomitant with type-I edge localized modes (ELMs). The response of electron density
edge profiles and temperature and pressure pedestal-top values to MPs are reported. ELM
mitigation is observed above an edge density threshold and independent of the MPs being
resonant or non-resonant with the edge safety factor. The edge electron collisionality appears
not to be appropriate to separate mitigated from non-mitigated discharges for the present
high-collisionality plasmas. No significant change in the position or gradient of the edge
density profile could be observed for the transition into the ELM-mitigated phase, except from
the effect of the three-dimensional MP field which leads to an apparent profile shift. An
increase in the density and decrease in the temperature at the pedestal-top balance such that the
pressure saturates at the value of the pre-mitigated phase. The plasma stored energy, the
normalized plasma pressure, and the H-mode quality factor follow closely the evolution of the
pedestal-top pressure and thus remain almost unaffected. The temporal evolution of the ion
effective charge shows that the impurity content does not increase although flushing through
type-I ELMs is missing. The type-I ELMs are replaced in the mitigated phase by small-scale
and high-frequency edge perturbations. The effect of the small bursts on the density profile,
which is correlated with a transient increase of the divertor thermoelectric current, is small
compared with the effect of the type-I ELMs. The residual scatter of the profiles in the
mitigated phase is small directly after the transition into the ELM-mitigated phase and
increases again when the pressure saturates at the value of the pre-mitigated phase.