[en] The EM induced power load on the divertor occurring in the type-I ELMy H-mode reference scenario is one of the main areas of concern for ITER. Extrapolating the results of present day tokamaks, an acceptable lifetime for the divertor cannot be realised. ELM mitigation by externally induced ELMS aim on a modification of the ELM frequency f_ELM, causing a reduction of the ELM energy ΔW_ELM by enhancing f_ELM. Various methods, usually targeting the ELM drive terms edge pressure gradient p_edge and current j_edge, have been tested. Some have shown to trigger prompt ELMs, establish f_ELM as a free parameter and mitigate ELMs according to the relation f_ELM x ΔW_ELM= const. The deleterious impact of ELM mitigation on the confinement is quite small, a relation for the plasma energy W∼f''-0.2_ELM was found. This is significantly less than W∼ f''-0.2_ELM observed in the case of intrinsic ELMs. Meanwhile, ELM frequency control already became a part of the toolkit for plasma control and is incorporated e. g. into integrated plasma scenarios as candidate regimes for ITER. Detailed investigations are performed at ASDEX Upgrade aiming to resolve the following puzzles connected with ELM trigger attempts relying on particle injection. This is the impact of the different trigger attempts relying on particle injection. This is the impact of the different trigger techniques, how the triggered ELM evolves temporally and spatially and why the correlation between local edge parameters like the collisionality ν and ΔW_ELM observed for intrinsic ELM can be broken. Local 3D perturbations were imposed by Deuterium (D) pellet injection, supersonic D gas jets, and Carbon and Aluminium micro pellet laser blow off. It is found that the gas jet, unlike the pellet, is insufficient to trigger prompt ELMs although the applied particle flux is of the same amount. On the other hand, investigations showed pellet masses reduced by more than a factor of ten-technically not feasible to date-would be still sufficient to release prompt ELMs. This shows that the perturbation required for ELM triggering has to fulfil local susceptibility criteria. Experiments conducted in order to uncover possible relations are reported as well as approaches to resolve the temporal and spatial evolution of a triggered ELMs with maximised resolution and compare it to its intrinsic counterparts. Furthermore, a fast framing camera system was set into operation for dedicated studies on the ELM trigger dynamics. The pellet based ELM pacing approach will be discussed with respect to its potential extension towards higher rations f_ELM /f_o(f_o: intrinsic ELM frequency). Experimental efforts at ASDEX Upgrade and its application to JET will be described. Finally, a possible scheme for pellet ELM pacing at ITER will be presented. (Author)