ELM behaviour and linear MHD stability of edge ECRH heated ASDEX Upgrade plasmas

Burckhart, A.; Dunne, M.; Wolfrum, E.; Fischer, R.; McDermott, R. M.; Viezzer, E.; Willensdorfer, M.

doi:10.1088/0029-5515/56/5/056011

Cited by 12 publications

(9 citation statements)

References 34 publications

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“…The goal of the experiments presented in this section is to test whether an edge deposition of the ECRH power has an impact on the behaviour of the plasma profiles during the ELM cycle and on the ion heat transport. Previous experiments on AUG showed that the application of edge ECRH heating affected the ELM frequency and caused a small relaxation of the edge gradients, while the MHD stability boundary remained unchanged [23]. A second, higher frequency ELM band appeared when depositing more ECRH power to the edge.…”

Section: On-and Off-axis Ecrh Heatingmentioning

confidence: 86%

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Investigation of inter-ELM ion heat transport in the H-mode pedestal of ASDEX Upgrade plasmas

et al. 2016

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Section: On-and Off-axis Ecrh Heatingmentioning

confidence: 86%

“…As shown in figure 1, at these medium density levels the edge ECRH has hardly an impact on the plasma parameters, including the ELM frequency. Note that in [23] the deposition location could be moved even further towards the plasma edge, i.e. ρ ≈ 0.88 pol .…”

Section: On-and Off-axis Ecrh Heatingmentioning

confidence: 99%

Investigation of inter-ELM ion heat transport in the H-mode pedestal of ASDEX Upgrade plasmas

et al. 2016

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“…On the other hand, it has been seen earlier in TCV that the ELM frequency has increased by a factor of 2 and the energy loss per ELM is reduced by the same factor when ECH deposition is shifted to the pedestal region from well inside the plasma boundary, while keeping the total input power constant [32]. When ECH is applied at the edge of AUG plasmas, the ELM frequency increased, and pedestal gradients relaxed without changing the MHD stability boundary [34]. Hence, 'how long' the inter-ELM period will be and 'why' for a given heating scenario, are still unresolved issues for the pedestal.…”

Section: Introductionmentioning

confidence: 93%

Evolution of ELMs, pedestal profiles and fluctuations in the inter-ELM period in NBI- and ECH-dominated discharges in DIII-D

et al. 2021

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In DIII-D, it has been observed that ELM frequency decreases by 40% and ELM spacing becomes more regular in time when heating is changed from pure neutral beam injection (NBI) to predominantly electron cyclotron heating (ECH) in ITER similar shape plasmas. In comparison with the pure NBI discharges, pedestal fluctuations in magnetics and density increase in the ECH-dominated discharges. Recovery of the pedestal profiles like electron density (n e), temperature (T e) and pressure (p e) shows marked differences for these two heating schemes. Average profiles in the last 30% of the ELM cycle show higher T e, lower n e, and similar p e at the pedestal top for the ECH discharge when compared to the NBI discharge. The gradient of T e (∇T e) is also steeper at the pedestal in the ECH discharge. Magnetic fluctuations show three distinct modes at 13–116 kHz in the ECH discharges only. n e fluctuations show two modes evolving in the inter-ELM period of the ECH discharge, a low-frequency (400 kHz) quasi-coherent mode (LFQC) and high-frequency (∼2 MHz) broadband (HFB) fluctuations. Evolution of these modes has marked correspondence with the inter-ELM ∇T e recovery. A sharp decrease in the D α baseline is observed whenever the LFQC weakens and the HFB grows, prior to each large ELM. Transport coefficients obtained from TRANSP show that MTM and/or TEM are plausible candidates for the observed fluctuations. Linear gyrofluid simulation (TGLF) corroborates this characterization. TGLF shows that the linear growth rate of the most dominant mode peaks at ion-scale (k θ ρ s ∼ 0.4) at the pedestal steep gradient and the frequency is in the electron diamagnetic direction. It is proposed that increased fluctuations in the ECH-dominated case, due to increased ∇T e, caused an increase in fluctuation-driven transport in the pedestal and slowed the pedestal recovery between ELMs, leading to a reduction in the ELM frequency.

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“…The MHD stability is parameterized here in terms of the maximum normalized edge pressure gradient α max [39] and flux-surface averaged edge current density j tor . The lines show the stability boundary defined with the criterion used in [40] for both I-mode and H-mode. Above the stability boundary, peelingballooning modes are unstable and type-I ELMs occur.…”

Section: Mhd Stabilitymentioning

confidence: 99%

I-mode pedestal relaxation events at ASDEX Upgrade

Silvagni,

Eich,

Happel

et al. 2020

Preprint

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The I-mode confinement regime can feature small edge temperature drops that can lead to an increase in the energy deposited onto the divertor targets. In this work, we show that these events are associated with a relaxation of both electron temperature and density edge profiles, with the largest drop found at the pedestal top position. Stability analysis of edge profiles reveals that the operational points are far from the ideal peeling-ballooning boundary. Also, we show that these events appear close to the H-mode transition in the typical I-mode operational space in ASDEX Upgrade, and that no further enhancement of energy confinement is found when they occur. Moreover, scrape-off layer transport during these events is found to be very similar to type-I ELMs, with regard to timescales (≈ 800 µs), filament propagation, toroidally asymmetric energy effluxes at the midplane and asymmetry between inner and outer divertor deposited energy. In particular, the latter reveals that more energy reaches the outer divertor target. Lastly, first measurements of the divertor peak energy fluence are reported, and projections to ARC -a reactor designed to operate in I-mode -are drawn.

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ELM behaviour and linear MHD stability of edge ECRH heated ASDEX Upgrade plasmas

Cited by 12 publications

References 34 publications

Investigation of inter-ELM ion heat transport in the H-mode pedestal of ASDEX Upgrade plasmas

Investigation of inter-ELM ion heat transport in the H-mode pedestal of ASDEX Upgrade plasmas

Evolution of ELMs, pedestal profiles and fluctuations in the inter-ELM period in NBI- and ECH-dominated discharges in DIII-D

I-mode pedestal relaxation events at ASDEX Upgrade

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