Scrape-off layer ion temperature measurements at the divertor target during type III and type I ELMs in MAST measured by RFEA

Elmore, S.; Allan, S.; Fishpool, G.; Kirk, A.; Thornton, A.; Walkden, N.; Harrison, James R.

doi:10.1088/0741-3335/58/6/065002

Cited by 8 publications

(6 citation statements)

References 29 publications

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“…Divertor measurements in the low density scenario were made using a fast sweep technique (FST) where the grid 1 voltage was swept at a faster frequency of 20kHz [27]. This allowed each filament to be measured by several sweeps, each lasting 50 µs.…”

Section: Divertor Measurementsmentioning

confidence: 99%

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Allan

Elmore

Fishpool

et al. 2016

Plasma Phys. Control. Fusion

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Abstract. Retarding field energy analysers (RFEAs) have been used to compare the ion temperature (T i ) of large plasma filaments with the background plasma (composed of small scale filaments) at the midplane and divertor target in L mode discharges in the Mega Amp Spherical Tokamak (MAST). At low densities, at the midplane and divertor, at distances from 2 to 4cm from the separatrix the temperature of ions in large filaments was found to be 2 to 3 times larger than the background plasma. At the midplane, the electron temperature for both large filaments and background plasma was around 3 to 7 times smaller than the ion temperature and had a flat profile across the scrape off layer (SOL). At higher densities, at the midplane and divertor, both the filament and background ion temperatures were smaller than at low density. At the midplane, the filament and background ion and electron temperature profiles across the SOL were relatively flat and of comparable magnitude, ranging in temperature from 5 to 25eV.

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Section: Divertor Measurementsmentioning

confidence: 99%

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Allan

Elmore

Fishpool

et al. 2016

Plasma Phys. Control. Fusion

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“…Ion temperature measurements have been made for the filaments arriving at the divertor during ELMs using an RFEA in a fast sweep mode [72]. As well as showing that the ion temperature in the filaments is much larger than the electron temperature, they have revealed that in a certain category of ELMs the filaments arrive at the target over an extended time (>1 ms), compared to the normal duration of 200-300 µs.…”

Section: Elm Physicsmentioning

confidence: 99%

Overview of recent physics results from MAST

Kirk¹,

Adámek²,

Akers³

et al. 2017

Nucl. Fusion

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New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance.

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“…The secondary filaments have been seen to extend the duration of the D α decay at the midplane and the ion current at the target [26]. In order to understand what effect these secondary filaments have on the heat flux profiles, a comparison of the D α duration and the duration of the target heat flux decay has been made between LSN and DND plasmas.…”

Section: Elm Database Used For Analysis Of Target Datamentioning

confidence: 99%

“…Application of this cut on the pedestal temperature produces a database of type I ELMs which con sists of 84 LSN ELMs and 15 DND ELMs. The analysis of the target footprints and timescales in LSN data can be complicated by the existence of secondary fila ments that are a result of the interaction of the ELM filaments with coils or support structures inside the vessel [26]. The sec ondary filaments have been seen to extend the duration of the D α decay at the midplane and the ion current at the target [26].…”

Section: Elm Database Used For Analysis Of Target Datamentioning

confidence: 99%

The role of ELM filaments in setting the ELM wetted area in MAST and the implications for future devices

Thornton

Allan

Dudson

et al. 2016

Plasma Phys. Control. Fusion

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Abstract. The ELM wetted area is a key factor in the peak power load during an ELM, as it sets the region over which the ELM energy is deposited. The deposited heat flux at the target is seen to have striations in the profiles that are generated by the arrival of filaments ejected from the confined plasma. The effect of the filaments arriving at the target on the ELM wetted area, and the relation to the midplane mode number is investigated in this paper using infrared (IR) thermography and high speed visible imaging (>10kHz). Type I ELMs are analysed, as these have the largest heat fluxes and are observed to have toroidal mode numbers of between 5 and 15. The IR profiles during the ELMs show clear filamentary structures that evolve during the ELM cycle. An increasing number of striations at the target is seen to correspond to an increase in the wetted area. Analysis shows that the ratio of the ELM wetted area to the inter-ELM wetted area, a key parameter for ITER, for the type I ELMs is between 3 and 6 for lower single null plasmas and varies with the ELM midplane mode number, as determined by visible measurements. Monte-Carlo modelling of the ELMs is used to understand the variation seen in the wetted area and the effect of an increased mode number; the modelling replicates the trends seen in the experimental data and supports the observation of increased toroidal mode number generating larger target ELM wetted areas. ITER is thought to be peeling unstable which would imply a lower ELM mode number compared to MAST which is peeling-ballooning unstable. The results of this analysis suggest that the lower n peeling unstable ELMs expected for ITER will have smaller wetted areas than peeling-ballooning unstable ELMs. A smaller wetted area will increase the level of ELM control required, therefore a key prediction required for ITER is the expected ELM mode number.* For full list of contributors, see http://www.euro-fusionscipub.org/mst1

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Scrape-off layer ion temperature measurements at the divertor target during type III and type I ELMs in MAST measured by RFEA

Cited by 8 publications

References 29 publications

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Overview of recent physics results from MAST

The role of ELM filaments in setting the ELM wetted area in MAST and the implications for future devices

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