Pfirsch-Schluter currents in the JET divertor

Schaffer, M. J.; Chankin, A.; Guo, Heng; Matthews, G. F.; Monk, R.D.

doi:10.1088/0029-5515/37/1/i07

Cited by 37 publications

(31 citation statements)

References 22 publications

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“…A bi-polar current in a narrow region at or near the separatrix strike point has been identified [3] in JET as being driven by the Pfirsch-Schlüter effect in the SOL. The total width of the negative lobe of this bi-polar feature was about 2 mm, when mapped to the outboard mid-plane.…”

Section: Return Current Pathmentioning

confidence: 99%

Observation of SOL current correlated with MHD activity in NBI heated DIII-D tokamak discharges

et al. 2004

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This work investigates the potential roles played by the scrape-off-layer current (SOLC) in MHD activity of tokamak plasmas, including effects on stability. SOLCs are found during MHD activity that are: (1) slowly growing after a mode-locking-like event, (2) oscillating in the several kHz range and phase-locked with magnetic and electron temperature oscillations, (3) rapidly growing with a sub-ms time scale during a thermal collapse and a current quench, and (4) spiky in temporal behavior and correlated with spiky features in D a signals commonly identified with the edge localized mode (ELM). These SOLCs are found to be an integral part of the MHD activity, with a propensity to flow in a toroidally non-axisymmetric pattern and with magnitude potentially large enough to play a role in the MHD stability. Candidate mechanisms that can drive these SOLCs are identified: (a) toroidally non-axisymmetric thermoelectric potential, (b) electromotive force (EMF) from MHD activity, and (c) flux swing, both toroidal and poloidal, of the plasma column. An effect is found, stemming from the shear in the field line pitch angle, that mitigates the efficacy of a toroially non-axisymmetric SOLC to generate a toroially nonaxisymmetric error field. Other potential magnetic consequences of the SOLC are identified: (i) its error field can introduce complications in feedback control schemes for stabilizing MHD activity, and (ii) its toroidally non-axisymmetric field can be falsely identified as an axisymmetric field by the tokamak control logic and in equilibrium reconstruction. The radial profile of a SOLC observed during a quiescent discharge period is determined, and found to possess polarity reversals as a function of radial distance.

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Section: Return Current Pathmentioning

confidence: 99%

Observation of SOL current correlated with MHD activity in NBI heated DIII-D tokamak discharges

et al. 2004

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“…Parallel energy transport is determined by classical conduction and convection, with kinetic corrections to heat diffusivities χ //i,e at low (separatrix) collisionalities ν i,e * , whilst diamagnetic transport is governed by a mix of classical (E×B, B×∇B, curvature, diamagnetic, etc.) and anomalous drifts [11,25,32,33]. Perpendicular, or radial, energy transport is turbulent in nature, with typical heat diffusivities in the range χ ⊥ SOL ~ 0.1-1 m 2 /s, well in excess of classical diffusion (<10 -3 m 2 /s).…”

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confidence: 99%

Chapter 4: Power and particle control

Divertor¹,

Database²,

Editors³

1999

Nucl. Fusion

282

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Abstract.Progress, since the ITER Physics Basis publication, in understanding the processes that will determine the properties of the plasma edge and its interaction with material elements in ITER is described. Experimental areas where significant progress has taken place are : energy transport in the SOL in particular of the anomalous transport scaling, particle transport in the SOL that plays a major role in the interaction of diverted plasmas with the main chamber material elements, ELM energy deposition on material elements and the transport mechanism for the ELM energy from the main plasma to the plasma facing components, the physics of plasma detachment and neutral dynamics including the edge density profile structure and the control of plasma particle content and He removal, the erosion of low and high Z materials in fusion devices, their transport to the core plasma and their migration at the plasma edge including the formation of mixed materials, the processes determining the size and location of the retention of tritium in fusion devices and methods to remove it and the processes determining the efficiency of the various fuelling methods as well as their development towards the ITER requirements. This experimental progress has been accompanied by the development of modelling tools for the physical processes at the edge plasma and plasma-materials interaction and the further validation of these models by comparing their predictions with the new experimental results. Progress in the modelling development and validation has been mostly concentrated in the following areas : refinement of the predictions for ITER with plasma edge modelling codes by inclusion of detailed geometrical features of the divertor and the introduction of physical effects, which can play a 2 major role in determining the divertor parameters at the divertor for ITER conditions such as hydrogen radiation transport and neutral-neutral collisions, modelling of the ion orbits at the plasma edge, which can play a role in determining power deposition at the divertor target, models for plasma-materials and plasma dynamics interaction during ELMs and disruptions, models for the transport of impurities at the plasma edge to describe the core contamination by impurities and the migration of eroded materials at the edge plasma and its associated tritium retention and models for the turbulent processes that determine the anomalous transport of energy and particles across the SOL. The implications for the expected performance of the reference regimes in ITER, the operation of the ITER device and the lifetime of the plasma facing materials are discussed. Introduction.This chapter outlines the significant progress achieved since the ITER Physics Basis in understanding basic scrape-off layer (SOL) and divertor processes in a tokamak. The interaction of plasma with first-wall surfaces will have considerable impact on the performance of fusion plasmas, the lifetime of plasma facing components, and the retention of tritium in next step Burning Plasma E...

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“…Since accurate equilibrium mapping with respect to the outer midplane position is essential to obtain pressure balance along field lines, the position of the separatrix strike point on the target is assigned by the sign change of the floating potential or target electric currents, which is expected to occur very close to the strike point due to the effect of Pfirsch-Schlüter currents for attached conditions [6]. Despite the fact that the physics of the target currents is expected to be more complex during ELMs, we use the experimentally well pronounced sign change of V f loat during the ELM-related strike point movement as separatrix marker.…”

Section: Divertor Profilesmentioning

confidence: 99%

Pressure balance between midplane and inner and outer divertor in ASDEX Upgrade H-mode discharges

Kallenbach

Dux

Eich

et al. 2009

Journal of Nuclear Materials

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Electron pressure profiles have been obtained in the outer midplane and along the divertor target using various diagnostics in ASDEX Upgrade. Inter-ELM and ELM phases of Hmode discharges with different power-and neutral fluxes in the divertor are investigated.To check the parallel pressure balance, mapping using equilibrium reconstruction is corrected/checked by physics constraints, like the upstream separatrix temperature according to power balance. Good agreement between the midplane pressure and the divertor pressure obtained from Langmuir probe measurements, assuming a Mach flow = 1 into the sheath, is observed for the outer scrape-off layer (SOL). A pressure reduction around the strike point by more than one order of magnitude is observed for low power, high neutral flux conditions. Strong detachment/pressure loss is seen in the inner divertor for all conditions. During ELMs, higher electron pressures are obtained in the outer divertor SOL compared to the midplane.

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Pfirsch-Schluter currents in the JET divertor

Abstract: DISCLAIMER

Cited by 37 publications

References 22 publications

Observation of SOL current correlated with MHD activity in NBI heated DIII-D tokamak discharges

Observation of SOL current correlated with MHD activity in NBI heated DIII-D tokamak discharges

Chapter 4: Power and particle control

Pressure balance between midplane and inner and outer divertor in ASDEX Upgrade H-mode discharges

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