Resonant-like behaviour during edge-localised mode cycles in the Joint European Torus

Webster, A. J. F.; Morris, J.; Todd, T.N.; Brezinsek, S.; Coad, P.; Likonen, J.; Rubel, M.; Contributors, Jet

doi:10.1063/1.4927755

Cited by 4 publications

(5 citation statements)

References 17 publications

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“…29-31 found the "simplest and clearest evidence" for the involvement of the control system in natural ELMing to be in toroidal full flux loop signals. In addition 35 identified vertical displacements, consistent with a mechanism analogous to the magnetic kick experiments.…”

Section: Discussionsupporting

confidence: 64%

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Control system-plasma synchronization and naturally occurring edge localized modes in a tokamak

et al. 2018

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Edge Localised Modes (ELMs) naturally occur in tokamak plasmas in high confinement mode. We find in ASDEX Upgrade that the plasma can transition into a state in which the control system field coil currents, required to continually stabilize the plasma, continually oscillate with the plasma edge position and total MHD energy. These synchronous oscillations are one-to-one correlated with the occurrence of natural ELMs; the ELMs all occur when the control system coil current is around a specific phase. This suggests a phase synchronous state in which nonlinear feedback between plasma and control system is intrinsic to natural ELMing, and in which the occurrence time of a natural ELM is conditional on the phase of the control system field coil current.

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Section: Discussionsupporting

confidence: 64%

“…This possibility was then explored on JET by Ref. 35 who as in Refs. 29-31 found the "simplest and clearest evidence" for the involvement of the control system in natural ELMing to be in toroidal full flux loop signals.…”

Section: Discussionmentioning

confidence: 99%

Control system-plasma synchronization and naturally occurring edge localized modes in a tokamak

et al. 2018

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“…A similar banding of ELM periods was observed in [36,37] by averaging over many similar discharges. Here we observe such features even within a single discharge.…”

Section: Elm Characteristicssupporting

confidence: 73%

“…For the discharges studied in [36,37], it was postulated that the ELMs might be paced by an oscillation of the plasma position caused by the control system. Such an explanation would help to explain why the oscillation period is so constant across many discharges.…”

Section: Elm Characteristicsmentioning

confidence: 99%

Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall

et al. 2017

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The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, δ = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest

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“…However, the system integrates in 3 cm wide circular chords in the divertor and provides no spatial a) information at the inner target plate if the ISP is on the vertical target positioned. Coherent ELM-averaging technique was applied to the large number of ELMs [40] to study the W-related PSI in more detail. Figure 11…”

Section: Optical Emission Spectroscopy: W Gross Erosionmentioning

confidence: 99%

Erosion, screening, and migration of tungsten in the JET divertor

et al. 2019

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The erosion of tungsten (W), induced by the bombardment of plasma and impurity particles, determines the lifetime of plasma-facing components as well as impacting on plasma performance by the influx of W into the confined region. The screening of W by the divertor and the transport of W in the plasma determines largely the W content in the plasma core, but the W source strength itself has a vital impact on this process. The JET tokamak experiment provides access to a large set of W erosion-determining parameters and permits a detailed description of the W source in the divertor closest to the ITER one: (i) effective sputtering yields and fluxes as function of impact energy of intrinsic (Be, C) and extrinsic (Ne, N) impurities as well as hydrogenic isotopes (H, D) are determined and predictions for the tritium (T) isotope are made. This includes the quantification of intra- and inter-edge localised mode (ELM) contributions to the total W source in H-mode plasmas which vary owing to the complex flux compositions and energy distributions in the corresponding phases. The sputtering threshold behaviour and the spectroscopic composition analysis provides an insight in the dominating species and plasma phases causing W erosion. (ii) The interplay between the net and gross W erosion source is discussed considering (prompt) re-deposition, thus, the immediate return of W ions back to the surface due to their large Larmor radius, and surface roughness, thus, the difference between smooth bulk-W and rough W-coating components used in the JET divertor. Both effects impact on the balance equation of local W erosion and deposition. (iii) Post-mortem analysis reveals the net erosion/deposition pattern and the W migration paths over long periods of plasma operation identifying the net W transport to remote areas. This W transport is related to the divertor plasma regime, e.g. attached operation with high impact energies of impinging particles or detached operation, as well as to the applied magnetic configuration in the divertor, e.g. close divertor with good geometrical screening of W or open divertor configuration with poor screening. JET equipped with the ITER-like wall (ILW) provided unique access to the net W erosion rate within a series of 151 subsequent H-mode discharges (magnetic field: T, plasma current: MA, auxiliary power MW) in one magnetic configuration accumulating 900 s of plasma with particle fluences in the range of 5– in the semi-detached inner and attached outer divertor leg. The comparison of W spectroscopy in the intra-ELM and inter-ELM phases with post-mortem analysis of W marker tiles provides a set of gross and net W erosion values at the outer target plate. ERO code simulations are applied to both divertor leg conditions and reproduce the erosion/deposition pattern as well as confirm the high experimentally observed prompt W re-deposition factors of more than 95% in the intra- and inter-ELM phase of the unseeded deuterium H-mode plasma. Conclusions to the expected divertor conditions in ITER as...

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Resonant-like behaviour during edge-localised mode cycles in the Joint European Torus

Cited by 4 publications

References 17 publications

Control system-plasma synchronization and naturally occurring edge localized modes in a tokamak

Control system-plasma synchronization and naturally occurring edge localized modes in a tokamak

Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall

Erosion, screening, and migration of tungsten in the JET divertor

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