The dependence of confinement on the isotope mass in the core and the edge of AUG and JET-ILW H-mode plasmas
P. A. SchneiderC. AngioniL. FrassinettiL. HorváthM. MaslovF. AuriemmaM. CavedonC. ChallisE. DelabieM. DunneJ.M. FontdecabaJ. HobirkA. KappatouD. KeelingB. KurzanM. LennholmB. LomanowskiC. F. MaggiR. M. McDermottT. PütterichA. ThormanM. Willensdorferthe ASDEX Upgrade Teamthe EUROfusion MST TeamJet Contributors
15
Citation
45
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract Experiments in ASDEX Upgrade (AUG) and JET with the ITER-like wall (JET-ILW) are performed to separate the pedestal and core contributions to confinement in H-modes with different main ion masses. A strong isotope mass dependence in the pedestal is found which is enhanced at high gas puffing. This is because the ELM type changes when going from D to H for matched engineering parameters, which is likely due to differences in the inter ELM transport with isotope mass. The pedestal can be matched in H and D plasmas by varying only the triangularity and keeping the engineering parameters relevant for core transport the same. With matched pedestals Astra/TGLF (Sat1geo) core transport simulations predict the experimental profiles equally well for H and D. These core transport simulations show a negligible mass dependence and no gyro-Bohm scaling is observed. However, to match the experimental observations at medium β it is required to take the fast-ion dilution and rotation into account. This is not enough for high β plasmas where for the first time a profile match between H and D plasmas was achieved experimentally. Under these conditions quasilinear modelling with TGLF over predicts the transport in the core of H and D plasmas alike.Keywords:
Pedestal
ASDEX Upgrade
Abstract In this work, we explore the pedestal properties of negative triangularity discharges with upper triangularity of δ u ≈ − 0.35 and with both ion ∇ B drift directions. In all cases, the discharges undergo a transition to H-mode with accompanying edge-localized modes (ELMs) that are not explained by the peeling-ballooning stability analysis alone. A variation in the ion ∇ B drift direction is observed. A lower pressure gradient, shallower radial electric field well and increased temperature fluctuations are measured in the favorable case. In addition, irregular ELMs are present. This difference is more pronounced in electron cyclotron resonance heating (ECRH) plasmas compared to plasmas with combined neutral beam injection and ECRH. A comparative analysis between two discharges, featuring similar plasma parameters but varied shaping, suggests that an interplay between other parameters, such as magnetic shear, the timing of the auxiliary heating and shaping, might play a strong role in low- to high-confinement transitions. While the low shaping discharge maintained L-mode, the high shaping discharge entered H-mode with ELMs, contrary to expectations.
ASDEX Upgrade
Pedestal
Upgrade
Cite
Citations (0)
Results of experimental scans of heating power, plasma shape, and nitrogen content are presented, with a focus on global performance and pedestal alteration.In detailed scans at low triangularity, it is shown that the increase in stored energy due to nitrogen seeding stems mainly from the pedestal, with a small additional contribution from increased core density peaking.It is also shown that the confinement increase is driven through the temperature pedestal at the three heating power levels studied.In a triangularity scan, an orthogonal effect of shaping and seeding is observed, where increased plasma triangularity increases the pedestal density, while impurity seeding (carbon and nitrogen) increases the pedestal temperature in addition to this effect.Modelling of these effects was also undertaken, with interpretive and predictive models being employed.The interpretive analysis shows a general agreement of the experimental pedestals in separate power, shaping, and seeding scans with peelingballooning theory.Predictive analysis was used to isolate the individual effects, showing that the trends of additional heating power and increased triangularity can be recoverd.However, a simple change of the effective charge in the plasma cannot explain the observed levels of confinement improvement in the present models.
Pedestal
ASDEX Upgrade
Cite
Citations (42)
Pedestal
ASDEX Upgrade
Pressure gradient
Cite
Citations (0)
ASDEX Upgrade
Pedestal
Mode (computer interface)
Electron temperature
Cite
Citations (0)
Pedestal
ASDEX Upgrade
Upgrade
Cite
Citations (0)
AbstractStudies in ASDEX Upgrade of the phenomenology and scaling of the H-mode transition, of edge-localized modes (ELMs), and characterization of the H-mode edge transport barrier carried out in various experimental campaigns between 1996 and 2001 are described. The H-mode transition is recognized by formation of a radial electrical field at the plasma boundary, which in ASDEX Upgrade is detected by an associated increase of the neutral particle charge exchange flux from ripple trapped particles. A scaling for the critical local edge temperature for the H-mode transition threshold is found. Similarity experiments with ASDEX Upgrade and Joint European Torus plasmas for the H-mode transition indicate that the H-mode transition can be obtained at the same values of dimensionless parameters ρ*, ν*, and β at the plasma edge, indicating that the threshold scaling is normally not dominated by atomic physics processes. Energy losses due to ELMs are examined. Different types of ELMs can be obtained, depending on plasma edge temperature and magnetics configuration. An interesting regime is the type II ELMy H-mode for configurations near double null, where the peak heat flux to the target is much reduced compared to large type I ELMs. High-resolution Thomson scattering measurements show that the edge transport barrier width in ASDEX Upgrade shows only weak variations, while the pedestal top electron pressure and pressure gradient strongly depend on the plasma current, or value of Bt/q95.
ASDEX Upgrade
Pedestal
Mode (computer interface)
Gyrokinetics
Cite
Citations (5)
The plasma shape, in particular the triangularity (δ), impacts on the pedestal stability.A scan of δ including a variation of heating power (P heat ) and gas puff was performed to study the behaviour of edge localised modes (ELMs) and the pre-ELM pedestal stability for different plasma shapes.Generally, at higher δ the pedestal top electron density (n e ) is enhanced and the ELM repetition frequency (f ELM ) is reduced.For all δ, the pedestal top n e is already fully established to its pre-ELM value during the initial recovery phase of the n e pedestal, which takes place immediately after the ELM crash.The lowering of the f ELM with increasing δ is related to longer pedestal recovery phases, especially the last pre-ELM phase with clamped pedestal gradients (after the recovery phases of the n e and electron temperature (T e ) pedestal) is extended.In all investigated discharge intervals, the pre-ELM pedestal profiles are in agreement with peeling-ballooning (PB) theory.Over the investigated range of δ, two well-separated f ELM bands are observed in several discharge intervals.Their occurrence is linked to the inter-ELM pedestal stability.In both kinds of ELM cycles the pedestal evolves similarly, however, the 'fast' ELM cycle occurs before the global plasma stored energy (W MHD ) increases, which then provides a stabilising effect on the pedestal, extending the inter-ELM period in the case of the 'slow' ELM cycle.At the end of a 'fast' ELM cycle the n e profile is radially shifted inwards relative to the n e profile at the end of a 'slow' ELM cycle, leading to a reduced pressure gradient.The appearance of two f ELM bands suggests that the pedestal becomes more likely PB unstable in certain phases of the inter-ELM evolution.Such a behaviour is possible because the evolution of the global plasma is not rigidly coupled to the evolution of the pedestal structure on the timescales of an ELM cycle.Edge stability and inter-ELM dynamics at varied triangularity 2
ASDEX Upgrade
Pedestal
Cite
Citations (12)
ASDEX Upgrade
Pedestal
Cite
Citations (0)
The application of magnetic perturbations (MP) via coils mounted inside the vessel can lead to mitigated ELMs. At ASDEX Upgrade mitigation of ELMs is reliably achieved at high line averaged electron densities in the pedestal ( ne ��� > 0.65 nGW) [1,2]. Without MPs, however, small ELMs also appear with sufficient fuelling. In this work the pedestal top properties of discharges featuring mitigated ELMs with and without application of MPs are compared. It will be shown that the pedestal top conditions, at which the small, mitigated ELMs appear, are the same with and without the application of MP coils. In addition, high power discharges with mitigated ELMs are analysed.
ASDEX Upgrade
Pedestal
Cite
Citations (2)
Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan.
ASDEX Upgrade
Pedestal
Cite
Citations (92)