Type-I ELM substructure on the divertor target plates in ASDEX Upgrade

Abstract

In the ASDEX Upgrade tokamak, the power deposition structures on the divertor target plates during type-I edge localized modes (ELMs) have been investigated by infrared thermography. In addition to the axisymmetric strike line, several poloidally displaced stripes are resolved, identifying an ELM as a composite of several subevents. This pattern is interpreted as being a signature of the helical perturbations in the low field side edge during the non-linear ELM evolution. Based on this observation, the ELM related magnetic perturbation in the midplane can be derived from the target load pattern. In the start phase of an ELM collapse, average toroidal mode numbers around n ≈ 3-5 are found evolving to values of n ≈ 12-14 during the ELM power deposition maximum. Further information about the non-linear evolution of the ELM mode structure is obtained from statistical analyses of the spatial distribution, heat flux amplitudes and number of single stripes.

Application of AXUV diode detectors at ASDEX Upgrade

“…The post-ELM filaments observed by the AXUV diagnostic might be remanent structures of the ELM filaments [20][21][22] or might be correlated to the X-point fluctuations reported in 23 , for which the radiation might be intensified by the ELMs. ELM filaments rotate toroidally 22 .…”

“…These filaments are radially, poloidally and toroidally localized but have a life time of only a few hundreds of µs and toroidal mode numbers in the range of 4 to 14 21,22 .…”

A conceptual model of the magnetic topology and nonlinear dynamics of ELMs

“…These currents are consistent in time and space with the thermoelectric currents [10] invoked in the model presented above. In the divertor, heat flux patterns observed during ELMs in ASDEX-U [11] are seen to have multiple striations that resemble the intersections of homoclinic tangle lobes with the target plates as seen in Fig. 1(b).…”

Divertor asymmetry and scrape-off layer flow in various divertor configurations in Experimental Advanced Superconducting Tokamak

“…In contrast, with reversed magnetic field, i.e., the ion !B drift being directed away from X point, the divertor target parameter distribution is more symmetric between inner and outer divertors and, in some cases, even with a reversed divertor asymmetry. [1][2][3][4][5] Several mechanisms are considered to influence divertor asymmetry, such as diamagnetic drift, E Â B drift, Shafranov shift, divertor radiation, plasma rotation, as well as the effect of ballooning like transport and resulting asymmetry of inboard/outboard connection length. The asymmetry of connection length at inboard/outboard side also influences divertor asymmetry, especially for double null (DN) divertor operation.…”

“…[10][11][12][13]15 In addition, It has been demonstrated by the measurements of the SOL flow in different divertor configurations at both high field side (HFS) and low field side (LFS) in Alcator C-Mod tokamak 12,13 that a ballooning-like transport is the most important contributing mechanism to the asymmetry in the HFS-LFS SOL flow, albeit some other mechanisms, including toroidal plasma rotation and PS ion currents, also contribute. 5,12 Detailed analysis of poloidal particle flux has also been made to reveal dominating mechanisms for the SOL particle transport. 11 Experimental of the divertor asymmetry between the configurations with the ion !B drift away and toward the active X-point, thus demonstrating the effect of classical drifts.…”