Observation of the palm tree mode, a new MHD mode excited by type-I ELMs on JET

Koslowski, H. R.; Alper, B.; Borba, D.; Eich, T.; Sharapov, S. E.; Perez, C. P.; Westerhof, E.; Contributors, Jet‐Efda

doi:10.1088/0029-5515/45/3/006

Cited by 17 publications

(23 citation statements)

References 24 publications

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“…Thus there might be a flattening of the electron temperature profile correlated with the SMP. In principle, this would be compatible with an island structure of the SMP 15 .…”

Section: Temperature Perturbation Associated With Smpsmentioning

confidence: 80%

“…In addition to ELMs, various other H-mode edge instabilities have been reported to show a characteristic signature recorded by magnetic probes. For the edge snake [14], the palm tree mode [15] and the outer mode [16] this signature diverges from a sine towards phases of constant signal, periodically interrupted by solitary excursions.…”

Section: Observation Of Smps At the Elm Onsetmentioning

confidence: 99%

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Solitary magnetic perturbations at the ELM onset

et al. 2012

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Tokamak H-mode plasmas frequently exhibit edge-localized modes (ELMs). ELMs allow maintaining sufficient plasma purity and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. ASDEX Upgrade is now equipped with a set of fast sampling diagnostics, which is well suited to investigate the chain of events around the ELM crash with appropriate temporal resolution ( 10 µs).Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100 kHz. They are typically observed close (±100 µs) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10 km s −1 . A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than the corresponding numbers in linear stability calculations. In combination with strong peaking of the magnetic signals this results in a solitary appearance resembling modes like palm tree modes, edge snakes or outer modes. This behaviour has been quantified as solitariness and correlated with main plasma parameters.SMPs may be considered as a signature of the non-linear ELM phase originating at the separatrix or further inside. Thus they provide a handle to investigate the transition from linear to non-linear ELM phase. By comparison with data from gas puff imaging processes in the non-linear phase at or inside the separatrix and in the scrape-off layer (SOL) can be correlated. A connection between the passing of an SMP and the onset of radial filament propagation has been found. Eventually the findings related to SMPs may contribute to a future quantitative understanding of the non-linear ELM evolution.

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“…Thus there might be a flattening of the electron temperature profile correlated with the SMP. In principle, this would be compatible with an island structure of the SMP 15 .…”

Section: Temperature Perturbation Associated With Smpsmentioning

confidence: 80%

Section: Observation Of Smps At the Elm Onsetmentioning

confidence: 99%

Solitary magnetic perturbations at the ELM onset

et al. 2012

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“…We assume this energy loss channel is created by a change of the magnetic edge topology due to the ELM [26][27][28][29] , connecting the edge plasma with the divertor. A similar topology is observed when external or internal magnetic perturbations are present, e.g.…”

Section: Rotation Of Post-elm Filamentsmentioning

confidence: 99%

Application of AXUV diode detectors at ASDEX Upgrade

Bernert

Eich

Burckhart

et al. 2014

Review of Scientific Instruments

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In the ASDEX Upgrade tokamak a radiation measurement for a wide spectral range, based on semiconductor detectors, with 256 lines of sight (LOS) and a time resolution of 5 µs was recently installed. In combination with the foil based bolometry, it is now possible to estimate the absolutely calibrated radiated power of the plasma on fast timescales. This work introduces this diagnostic based on AXUV (Absolute eXtended UltraViolet) n-on-p diodes made by International Radiation Detectors, Inc. (IRD). The measurement and the degradation of the diodes in a tokamak environment is shown. Even though the AXUV diodes are developed to have a constant sensitivity for all photon energies (1 eV to 8 keV), degradation leads to a photon energy dependence of the sensitivity. The foil bolometry, which is restricted to a time resolution of less than 1 kHz, offers a basis for a time dependent calibration of the diodes. The measurements of the quasi-calibrated diodes are compared with the foil bolometry and found to be accurate on the kHz time scale. Therefore, it is assumed, that the corrected values are also valid for the highest time resolution (200 kHz). With this improved diagnostic setup, the radiation induced by edge localized modes (ELMs) is analyzed on fast timescales.

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“…Related to the occurence of expelled current carrying filaments observed in the SOL can be the socalled Palm Tree Mode, which is a ELM postcursor [47] and has been identified as a rotating closed current filament at a rational surface [48].…”

Section: Current Filaments Associated To Elmsmentioning

confidence: 99%

Profiles and Fluctuations in Edge and SOL Turbulence

Naulin

Vianello

et al. 2012

Contrib. Plasma Phys.

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The time and space averaged profiles of temperature, particle density, and momentum are in the scrape off layer determined by the intermittent transport generated at the edge shear layer. The distinction between profiles and fluctuations becomes arbitrary for situations where the transport is highly intermittent and shows long range correlations. Without this distinction the full range in parameter variability has to be taken into account for simulations, posing extreme demands on the used models. Numerical investigations and experimental results show how the interplay between radially propagating structures and parallel transport sets up the observed profiles and how intermittency influences edge conditions. The filamentary blob structures also transport and generate currents in the SOL, which can be investigated by means of local magnetic diagnostics. Finally, the ratio of ion to electron temperature in the SOL is an important measure for the influence of finite larmor radius effects on the propagation properties of blobs. Numerical investigations indicate that these effects can lead to an increased self confinement and radial reach of these structures.

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Observation of the palm tree mode, a new MHD mode excited by type-I ELMs on JET

Cited by 17 publications

References 24 publications

Solitary magnetic perturbations at the ELM onset

Solitary magnetic perturbations at the ELM onset

Application of AXUV diode detectors at ASDEX Upgrade

Profiles and Fluctuations in Edge and SOL Turbulence

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