Toroidal Asymmetry Research Articles

Tokamak plasma equilibria with n=1 toroidal asymmetry

A general approach of how to construct plasma equilibrium in a tokamak with n=1 violation of toroidal symmetry is proposed. For an arbitrary axisymmetric tokamak plasma equilibrium, there exists the small n=1 deformation of the initial magnetic configuration that keeps the nesting of the magnetic surfaces (as in the initial configuration) and provides plasma equilibrium; such deformation and final equilibrium configuration are calculated analytically. The asymmetric analogue of the Solov'ev's equilibrium with non-degenerated plasma pressure and current density profiles is presented as an example of the application of the developed algorithm.

VUV imaging of type-I ELM filamentary structures and their temporal characteristics on EAST

In the H-mode experiments conducted on the Experimental Advanced Superconducting Tokamak (EAST), fluctuations induced by the so-called edge localized modes (ELMs) are captured by a high-speed vacuum ultraviolet (VUV) imaging system. Clear field line-aligned filamentary structures are analyzed in this work. Ion transport induced by ELM filaments in the scrape-off layer (SOL) under different discharge conditions is analyzed by comparing the VUV signals with the divertor probe signals. It is found that convective transport along open field lines towards the divertor target dominates the parallel ion particle transport mechanism during ELMs. The toroidal mode number of the filamentary structure derived from the VUV images increases with the electron density pedestal height. The analysis of the toroidal distribution characteristics during ELM bursts reveals toroidal asymmetry. The influence of resonance magnetic perturbation (RMP) on the ELM size is also analyzed using VUV imaging data. When the phase difference of the coil changes periodically, the widths of the filaments change as well. Additionally, the temporal evolution of the ELMs on the VUV signals provides rise time and decay time for each single ELM event, and the results indicate a negative correlation trend between these two times.

Radiation asymmetry in JET disruption mitigation experiments with shattered pellet injection

In ITER, to mitigate the deleterious effects of plasma disruptions, massive quantities of radiating impurities will be injected into the disrupting plasma by shattered pellet injectors (SPI) to pre-emptively radiate away the stored thermal and magnetic energy (Lehnen et al Proc. 27th IAEA Fusion Energy Conf. (FEC 2018) (Gandhinagar, India) EX/P7-12). However, asymmetries in the radiation pattern could result in intense photon flashes during the thermal quench that could locally damage or erode the stainless steel plasma-facing surface of the diagnostic port plugs (Pitts et al 2015 J. Nucl. Mater. 463 748–75). Experiments have been undertaken at JET to assess the potential dependence of the radiated power asymmetry on plasma energy during SPI mitigated disruptions. Calculations of the toroidal asymmetry in the radiated power indicate that the toroidal peaking factor is largest near the SPI position and decreases with the plasma stored energy, which is a promising result in view of radiation heat loads during mitigated disruptions in ITER.

Interaction of SPI pellets with plasma on JET and associated disruptions

The presented data refer to the Shattered Pellet Injector (SPI) experiments carried out at JET in 2019–2020. This paper is a full journal version of the data originally presented as posters at TMPDM_2020 and EPS_2021. This paper presents various aspects of the interaction of pellets with plasma and associated disruptions. The experiment was performed with I p = (1.1–3.1) MA plasmas and mainly with Ne + D2 pellet composition, but also with Ar pellets. The Current Quench (CQ) time, τ 80−20, is the key characteristic of mitigation effectiveness. A pellet with a high content of Ne or Ar can reduce the CQ duration below the upper required JET threshold. Plasmas with high (thermal + internal poloidal magnetic) pre-disruptive plasma energy require a high content of Ne pellets to obtain a short CQ duration. Pellets with a small amount of Ne (and accordingly large amount of D), instead of causing a mitigated CQ, create the conditions for a ‘cold’ Vertical Displacement Events (VDE). The SPI was applied to plasma with different status: mainly to normal (‘healthy’) plasma, i.e. not prone to disruption, post-disruptive and VDE plasma. This study shows that SPI effectiveness in terms of CQ duration and, accordingly, EM loads does not depend on the state of the plasma, whether it is ‘healthy’ or post-disruptive plasma. SPI has been shown to reduce the axisymmetric vertical vessel reaction forces by about (30–40) % compared to unmitigated disruptions. On JET, the VDE, whether ‘hot’ or ‘cold’, always creates the conditions for a toroidal asymmetry in the plasma, so the VDE on the JET is referred to as Asymmetric VDE (AVDE). The interrupting of VDE and prevention of AVDE with SPI has been demonstrated. Thus, the effectiveness of disruption mitigation using SPI has been confirmed.

Poloidal structure of the edge parallel flow in H-mode, L-mode and I-mode confinement regimes

Impurity profiles have been measured with the edge high field side (HFS) and low field side (LFS) charge exchange recombination spectroscopy suite at ASDEX Upgrade enabling the study of the poloidal structure of the edge parallel flow in H-mode, L-mode and I-mode. In H-mode, asymmetries in the impurity density, toroidal and poloidal rotations are found. In I-mode, only toroidal rotation asymmetries have been measured while in L-mode no asymmetries have been observed. The measured parallel flow can be divided in two components, the Pfirsch–Schlüter (PS) flow and the symmetric flow. Two different methods have been followed to determine both contributions to the parallel flow. The first method is based on the calculation of the PS flow at the HFS and LFS from the radial electric field. The second method directly provides the symmetric flow from the flux surface average (FSA) of the parallel flow. In H-mode, the methods provide different results, while in L-mode and I-mode they agree. The differences observed in H-mode between the two methods could be explained by the existence of asymmetries in the impurity density, by the non-negligible particle sources and radial losses, or by the approximations made in the calculation of the FSA of the parallel flow from measurements in two poloidal positions (midplane HFS and LFS) only.

Statistical Properties of Pc4‐5 ULF Waves in Plasmaspheric Plumes

AbstractUltra‐low‐frequency (ULF) waves emerge as pivotal factors in elucidating the mechanisms that drive the intricate dynamics of radiation belt electrons within the plasmasphere and plasmaspheric plumes. Utilizing THEMIS data from September 2012 to September 2017, we conducted a comprehensive statistical analysis of Pc4‐5 ULF waves within and outside the plasmaspheric plume. Our findings reveal a distinctive dawn‐dusk asymmetry in occurrence rate and wave power of poloidal mode waves in the absence of the plume, resembling the toroidal mode asymmetry observed. Poloidal mode waves exhibit a higher likelihood of formation within the plume, while the toroidal mode waves show the opposite trend, contributing to the elevated dusk‐side occurrence rate of poloidal mode waves. Moreover, both wave modes within the plume demonstrate lower peak frequencies compared to waves outside the plume. The global distribution of wave power within the plume suggests higher power at noon than on the dusk side.

The mechanism of the global vertical force reduction in disruptions mitigated by massive material injection

Disruptions lead to a rapid loss of thermal and magnetic energy and can cause large heat loads, mechanical forces, and the excitation of a beam of relativistic runaway electrons. The operation of tokamaks at high energy and plasma current requires the use of a mitigation system to limit such detrimental effects. Mitigation techniques rely mainly on the injection of a large amount of impurities to radiate the majority of the thermal and magnetic energies. Heat loads and electro-magnetic (EM) forces as well as their toroidal asymmetries can be greatly reduced by such measures. In this paper, a theory is lined out to explain the reduction of the global vertical force based on large toroidal halo currents that keep the current centroid stationary in the midplane. As a consequence, the vertical current moment, which is linked to the EM-force, is reduced. The theory is backed up by experimental observations in shattered pellet injection mitigated vertical displacement event experiments in ASDEX Upgrade (AUG) and JET as well as by 2D simulations with the extended MHD code JOREK. Scans in the boundary heat flux are carried out to estimate the correct scrape-off layer temperature and the influence of the fraction of conducted energy. Finally, predictive simulations for ITER confirm the reduction of the vertical force by the injection of impurities.

Magnetohydrodynamic stability and the effects of shaping: a near-axis view for tokamaks and quasisymmetric stellarators

How much does the cross-section of a toroidal magnetic field configuration tell us about its magnetohydrodynamic (MHD) stability? It is generally believed that positive triangularity (typically leading to bean-shaped cross-sections with their indentation on the inboard side in stellarators) contributes positively to MHD stability. In this paper, we explore the basis of this statement within a near-axis description for axisymmetric and quasisymmetric magnetic configurations. In agreement with the existing literature, we show that positive triangularity stabilises vertically elongated tokamaks. In quasisymmetric stellarators, the toroidal asymmetry of flux surfaces modifies this relation. The behaviour of stellarator-symmetric, quasisymmetric stellarators can still be described in terms of the shape of one of their up–down symmetric cross-sections. However, we show that for a sample of quasisymmetric configurations, the positive-bean-shaped cross-sections do not contribute positively to stability. Unlike in the axisymmetric case, we also learn that finite $\beta$ can improve stability even without magnetic shear.

The shear Alfvén continuum with a magnetic island chain in tokamak plasmas

The shear Alfvén continuum spectrum is studied for a tokamak with a single island chain using the ideal magnetohydrodynamics theory. We have taken into account the toroidal geometry and toroidal mode coupling with the island considered as a highly-shaped stellarator. Various new frequency gaps open up inside the island due to its asymmetry both poloidally and toroidally, such as the mirror-induced Alfvén eigenmode (MAE) gap and the helicity-induced Alfvén eigenmode (HAE) gap. We have shown that the MAE gap acts as the continuation of the outside toroidal Alfvén eigenmode (TAE) gap into the island. However, the combined TAE/MAE gap is getting narrower as the island grows, leaving only half of its original width with a moderate island size as much as 3.2% of the minor radius. In addition, the two-dimensional eigenfunction of the continuum mode on the lower tip of the MAE gap now has highly localised structures around the island’s long axis, contrary to the usual oscillatory global solutions found with no or a low level of toroidal asymmetry—an indication of the continuous spectrum becoming discrete and dense. These results have implications for the frequency, mode structure and continuum damping of global TAEs residing in the gap.

Identification of fast ion wall loads in Wendelstein 7-X from thermographic measurements

Fast ion wall loads can result in excessively high heat fluxes to the plasma-facing components (PFCs). To allow for the development of mitigation strategies, and thereby protect the PFCs, the fast ion losses have to be predicted by faithful models. To ensure that fast ion models are an accurate representation of the real world, they need to be verified. The neutral-beam experiments performed in Wendelstein 7-X (W7-X) allow to investigate and verify models of the fast ion losses in the stellarator configuration. Infrared thermographic measurements were used to obtain the heat flux to both the baffle plates and the divertor. We found evidence of fast ion wall loads on the baffle plates, with loads between 100 kW m−2 and 1 MW m−2. The loads are attributed to fast ions which escape the main plasma via magnetic ripples. The fast ion wall loads on the baffle plates show up-down and toroidal asymmetry. The experimental results were compared to numerical simulations performed by the BEAMS3D and ASCOT codes. Qualitative agreement in up-down asymmetry is found, but the magnitude and toroidal asymmetry are not yet well predicted by the simulations. The asymmetries of the strike lines on the divertor suggest that fast ions also play a role here. Specifically, a second strike line emerged consistently in the high-iota configuration on the horizontal divertor. The shape and magnitude of the strike lines changed considerably during the neutral-beam injection (NBI) operation phase. Although no damage to steel components of W7-X was found, fast ion loads to the baffle plates could possibly limit the NBI operation in the upcoming campaigns of W7-X.

Three-dimensional structure of radiative cooling in impurity seeded plasmas in the Large Helical Device

• Three-dimensionally localization of radiative cooling due to nitrogen seeding for divertor detachment was detected experimentally. • Principal component analysis was applied to two-dimensional radiation images. • A radiation feature in nitrogen seeding was extracted as a principal component. • EMC3-EIRENE code suggested the ionization enhancement at one of the divertor legs. • The extracted feature along the magnetic field lines which pass through the divertor leg. Three-dimensionally localization of radiative cooling due to nitrogen (N 2 ) seeding for divertor detachment was detected experimentally. Since the localization along some magnetic field lines induces toroidal asymmetry of heat load reduction on divertor plates, it should be avoided for fusion reactors. The three-dimensionally localized structure was extracted using Principal Component Analysis (PCA) from two-dimensional radiation images measured with an InfraRed imaging Video Bolometer (IRVB). By applying PCA to 34 images each in N 2 seeded plasmas with toroidally-asymmetric heat load reduction and in neon (Ne) seeded plasmas with toroidally-symmetric heat load reduction, a radiation feature in N 2 seeded plasmas was found as one of the principal components (PC). The three-dimensional transport code EMC3-EIRENE indicated that the ionization in one of the divertor legs is enhanced in nitrogen seeding compared with Ne seeding due to the difference in the first ionization energy. The magnetic field lines from the divertor leg were along the extracted radiation structure and were terminated by the divertor where the heat load decreased due to the N 2 seeding. These results indicate that three-dimensionally localized structure of radiative cooling was detected experimentally.

Divertor plasma behaviors with neon seeding at different locations on EAST with ITER-like divertor

For the problem of excessively high divertor heat flux, active impurity seeding is an effective method to radiate the plasma energy reaching the divertor and thus achieve the divertor detachment. Neon is a very effective radiation impurity on many current tokamaks, which is also a candidate species to be applied on ITER. In the EAST 2019 experimental campaign, a series of experiments were performed by seeding a mixture of neon and deuterium (Ne-D2) for detachment and core-edge-divertor integration in H-mode plasmas. The divertor partial detachment with high-confinement core plasma has been achieved by using Ne-D2 seeding in EAST with ITER-like tungsten divertor. Both the plasma stored energy and H 98,y2 > 1.1 are maintained, with the divertor electron temperature, heat flux and the surface temperature near the strike point being all significantly reduced. The differences between Ne-D2 seeding at the scrape-off layer (SOL) upstream and downstream have been experimentally investigated in detail. It is found that impurity seeding at SOL downstream is more beneficial to reducing the divertor electron temperature and peak heat flux. By comparison with experiments using divertor D2 fueling, it is further demonstrated that gas seeding in the SOL downstream will enrich more particles near the strike point, while the seeding in the SOL upstream will influence the entire outer target more evenly. Furthermore, in most of the experiments, gas seeding does not cause obvious toroidal asymmetry in the divertor plasma. However, when D2 is injected in an amount similar to that used to build the plasma, it causes the particle flux near the gas-puff to increase locally, i.e., much more than that at the toroidal location far from the gas-puff location. It is a competition between particle source and transport. When the particle source is stronger, it will naturally increase the local particles. In addition, dedicated experiments with different poloidal distances between impurity seeding and strike point on the radiation ability were carried out. Both experimental results and SOLPS simulation show that the seeding close to the strike point is more conducive to neon ionization and energy radiation.

Effect of toroidal particle sources on SOL physics in the FT‐2 tokamak

AbstractTwo gas‐puffs are used near limiters in the FT‐2 tokamak for the purpose of hydrogen refuelling during plasma discharges. This creates toroidal and poloidal asymmetry in particle sources near limiters which has to be considered in modelling. Here, the effect of toroidal asymmetry is simulated using the gyrokinetic code ELMFIRE. Two slightly different toroidal particle sources are used in simulations, and their results are compared with each other, and with experimental measurements to understand the impact of toroidal particle sources on Scrape‐off Layer (SOL) physics.

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25%–50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.

Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)

Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, a shattered pellet injection (SPI) system was installed on JET and experiments conducted at a range of thermal energy fractions and stored energies in excess of 7 MJ. The primary goals of these experiments were to investigate the efficacy of the SPI on JET and the ability of the plasma to assimilate multiple pellets. Single pellet injections produced a saturation in total radiated energy (W rad) with increasing injected neon content, suggesting total radiation of stored thermal energy. Further increases in injected neon quantities resulted in reduced cooling times and current quench (CQ) durations, indicating higher impurity assimilation. No significant variation in CQ duration or W rad was observed when varying the deuterium content at fixed neon quantities. Higher assimilation, inferred by shorter CQ durations, was measured when a mechanical punch was used to launch the pellets and this was attributed to a lower pellet velocity leading to higher solid content in the pellet plume and larger fragments penetrating deeper into the plasma. Radiation asymmetries averaged over the cooling time were inferred from Emis3D and ranged from 1.6 to 1.9. Asymmetries averaged over the entire disruption sequence were found to increase at higher thermal energy fractions. The radiated energy fractions decreased with increasing thermal energy fractions but this trend was eliminated when toroidal asymmetries were accounted for with Emis3D. Pure deuterium pellets were able to produce cooling times of up to 75 ms with a gradual loss in thermal stored energy of up to 80%. Experiments with multiple pellet injection indicated W rad can be increased through pellet superposition and density can be increased with an additional D2 injection without a reduction in W rad. KPRAD modelling accurately reproduced the cooling times and the CQ duration at high thermal energies. Assimilation estimates from KPRAD indicated CQ rates scale strongly whilst W rad scales weakly and saturates with assimilated neon content. Comparable W rad can be achieved with lower assimilated neon quantities as longer cooling times are attained. Thus reduced neon content can be preferential in a thermal load mitigation scheme as it may reduce radiation asymmetries and prevent flash melting.

Modeling the toroidal asymmetry of the heat load impacted by nitrogen injection in EAST using EMC3-EIRENE

The effects of nitrogen injection on the heat load in the scape-off layer are systematically investigated in the EAST double-null divertor configuration using EMC3-EIRENE code. Nitrogen impurities injected near the separatrix line and away from the separatrix line give rise to a non-axisymmetric distribution of heat load on the target plate. With impurity injection near the separatrix line, the occurrence of the toroidal asymmetric heat load is observed only nearby the toroidal injection location, while with injection away from the separatrix line the regions of the asymmetric heat load extend and deviate from the toroidal injection position. The competition between the friction force and the ion temperature gradient force has been analyzed. It shows that when impurities are injected away from the separatrix line more impurities can be parallelly transported to a further toroidal location, which results in the extension and deviation of the non-symmetric electron temperature. When the input power is increased, the non-symmetric phenomenon of the heat load turns to be insignificant due to the reduction of the impurity density in the downstream regions, as illustrated by the field line tracing technique. Furthermore, by scanning various injection positions in the EAST tokamak, the optimum location of impurity injection has been discovered.

Penetration of n = 2 resonant magnetic field perturbations in EAST

This paper presents the penetration of n = 2 magnetic field perturbations, where n is the toroidal mode number. The n = 2 intrinsic error field (IEF) is measured in an ohmic heating plasma using the compass scan method, i.e. the toroidal asymmetry in the threshold current for the penetration of n = 2 resonant magnetic perturbations (RMPs). Its amplitude is 55.5 A in equivalent coil current or B r,3/2 = 0.1 G and the toroidal phase of the IEF is around 170.6° (129°). Phasing scans (scans of the phase difference between the upper and lower coil currents) of the n = 2 RMPs are carried out to obtain the effects of the n = 2 spectrum on field penetration. The observed dependence of the field penetration on the spectrum is consistent with those of simulations using the MARS-F code. One of the interesting phenomena is that the n = 2 mode often stimulates an n = 1 mode. The dominant poloidal harmonic of the n = 1 mode is m = 2, and the dominant poloidal harmonic of the n = 2 mode is m = 3. The evolution of the n = 1 mode has two stages, i.e., an initial small island growth stage, and a later saturation stage. In the initial stage, the amplitude of the n = 1 magnetic island grows, while the phase remains fixed. When the amplitude of the magnetic island exceeds a certain threshold, it enters the second stage, in which the magnetic island is locked into another phase and its amplitude starts to saturate. The phase in the initial small island stage depends linearly on the phase of the applied n = 2 RMP, which suggests that the n = 2 mode is directly driven by the coupling between the n = 1 and n = 2 modes. The phase in the second stage is either locked to the phase close to the previously measured n = 1 IEF, or is locked to the phase close to the n = 2 response field. This suggests that the final phase of the n = 1 mode depends on competition between the locking effect induced by the n = 1 IEF and the nonlinear coupling effect between the two modes. This might be an issue in the MHD control application using high-n RMPs in the future ITER device.

Transition from no-ELM response to pellet ELM triggering during pedestal build-up—insights from extended MHD simulations

Pellet edge localized mode (ELM) triggering is a well-established scheme for decreasing the time between two successive ELM crashes below its natural value. Reliable ELM pacing has been demonstrated experimentally in several devices, increasing the ELM frequency considerably. However, it was also shown that the frequency cannot be increased arbitrarily due to a so-called lag-time. During this time, after a preceding natural or triggered ELM crash, neither a natural ELM crash occurs nor is it possible to trigger an ELM crash by pellet injection. For this article, pellet ELM triggering simulations are advanced beyond previous studies in two ways. Firstly, realistic E × B and diamagnetic background flows are included. And secondly, the pellet is injected at different stages of the pedestal build-up. This allows us to recover the lag time for the first time in simulations and investigate it in detail. A series of nonlinear extended MHD simulations is performed to investigate the plasma dynamics resulting from an injection at different time points during the pedestal build-up. The experimentally observed lag-time is qualitatively reproduced. In particular, a sharp transition is observed between the regime where no ELMs can be triggered and the regime where pellet injection causes an ELM crash. Via variations of pellet parameters and injection time, the two regimes are studied and compared in detail, revealing pronounced differences in the nonlinear dynamics. The toroidal mode spectrum is significantly broader when an ELM crash is triggered, enhancing the stochasticity and therefore also the losses of thermal energy along magnetic field lines. In the heat fluxes to the divertor targets, pronounced toroidal asymmetries are observed. In the case of high injection velocities leading to deep penetration, the excitation of core modes like the 2/1 neoclassical tearing mode is also observed.

Development of a weighted sum estimate of the total radiated power from large helical device plasma.

Diagnosing the amount of radiated power is an important research goal for fusion devices. This research aims at better understanding and diagnosing the radiated power from the Large Helical Device (LHD). The current radiated power estimate in the LHD is based on one wide-angle resistive bolometer. Because the estimate stems from one bolometer location toroidally and has a wide-angle poloidal view, this estimate does not take into account toroidal and poloidal radiation asymmetries that are observed in the LHD in discharges with gas puffing. This research develops a method based on the EMC3-Eirene model to calculate the set of coefficients for a weighted-sum method of estimating the radiated power. This study calculates these coefficients by using a least-squares method to solve for a coefficient set, using a variety of simulated cases generated by the EMC3-Eirene model, combined with corresponding geometric radiated power density considerations. If this set of coefficients is multiplied by the detector signal of each bolometer and summed up, this gives a total radiated power estimate. This new estimate takes into account toroidal and poloidal asymmetries by using the bolometer channels viewing different toroidal and poloidal locations, thereby reducing the estimation error and providing information about toroidal asymmetries.

Study of detachment in future ASDEX Upgrade alternative divertor configurations by means of EMC3-EIRENE

ASDEX Upgrade is preparing a hardware modification of its upper divertor in order to study alternative divertor configurations, like the X-divertor (XD) and the snowflake divertor (SF), that are discussed as a possible solution for the power exhaust problem. Experiments characterizing the current upper divertor in single-null (SN) configuration before and during detachment were carried out recently and interpreted by EMC3-EIRENE (Lunt et al., 2020) now including volumetric recombination. In continuation of these studies we here report on further simulations with this code extrapolating these conditions to the future upper divertor. For the same transport parameters, input power and upstream separatrix density for which the outer target (OT) of the SN is attached, the XD and SF show significant detachment at the OT accompanied by a reduction of the parallel heat flux by a factor of more than five. Despite the shallow field line incidence angles in the XD configuration the intrinsic 3D error fields from the current feeds only cause toroidal variations of the power fluxes of the order of 10%. With a hypothetical misalignment of the divertor coils by 3 cm substantial asymmetries in the power deposition profile are found, however, even those vanish when going to detached plasma conditions. In order to fully detach the plasma at the OT in the SF configuration impurities, here in the form of nitrogen, need to be puffed directly into the region of the secondary X-point in the simulation. • ASDEX Upgrade is preparing a hardware modification of its upper divertor in order to study alternative divertor configurations. • Simulations validated against recent detached ASDEX Upgrade H-mode discharges and extrapolated to X-divertor and snowflake divertor configurations. • XD easier access to detachment. • 3D error fields from artificially misaligned coils cause strong toroidal asymmetries of the power deposition pattern under attached divertor conditions that vanish in detachment. • First detached SF configurations with EMC3-EIRENE.