Electric currents in the scrape-off layer in ASDEX Upgrade

Kallenbach, A.; Carlson, A.; Pautasso, G.; Peeters, A. G.; Seidel, U.; Zehrfeld, H. P.

doi:10.1016/s0022-3115(00)00445-1

Cited by 44 publications

(54 citation statements)

References 8 publications

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“…Good agreement is observed between experimental data and the thermoelectric current model, which is consistent with observations made on JT-60U [68], ASDEX-Upgrade [69], COMPASS [70], JET [71] and others. For the case shown here, the dominant driving term for thermoelectric current is the temperature asymmetry at the divertor targets.…”

Section: Thermoelectric Currentssupporting

confidence: 90%

Characterisation of detached plasmas on the MAST tokamak

Harrison

2011

Journal of Nuclear Materials

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The mitigation of the steady-state heat loading to plasma-facing components in the divertor structures is an essential prerequisite for the operation of next-generation conventional and tight aspect-ratio Tokamaks. Currently, the most attractive means of reducing this heat loading is the so-called "detached" regime, which is the primary focus of this study.This thesis describes work that was carried out on the MAST tokamak to accurately characterise the plasma conditions within divertor plasmas, and to test the validity of those measurements. To assist in this study, an interpretive code, OSM [1], has been upgraded with additional numerical schemes to ascertain the dominant mechanisms governing parallel scrape-off layer transport including flux expansion, dynamic viscosity and cross-field drift motion in attached conditions. It has been found that the invocation of flux expansion, parallel viscosity and diamagnetic drift motion assist the OSM numerical scheme to converge in the presence of (static+dynamic) parallel pressure gradients often observed between the outboard midplane and lower outer divertor leg.It has also been found that the ion pressure, which is currently unknown, could resolve the observed pressure discrepancy.Line-of-sight spectroscopy of high-n Balmer emission lines has been used to ascertain line averaged T e and line integrated n e during the detached phase of MAST discharges with high spatial resolution (≈ 7mm) to determine electron static pressure profiles along flux contours. Furthermore, narrow-bandwidth imaging spectroscopy of D α , D γ , CII and CIII emission during the onset and sustainment of detachment has been carried out with high temporal (5kHz) and spatial (≈ 3mm) resolution. These data have been combined with ion flux measurements to the divertor target plates using embedded Langmuir probes (6-9mm radial resolution) and upstream Thomson scattering measurements of n e , T e . The data was input into the OSM code, coupled with the kinetic neutral transport code EIRENE [2], to check the experimental data set for internal consistency. The experimental data collected has been used to reconstruct the plasma conditions within the detached divertor leg, heavily constrained by experimental data. EIRENE calculations with re-constructed plasma conditions are able to reproduce experimentally observed D γ /D α line emission ratios to within a factor iii iv of 2 within the recombining region. AcknowledgmentsThe work presented in this thesis is the culmination of the work of many people, who I gratefully acknowledge here. Foremost, I thank Dr. Steven Lisgo for his guidance, enthusiasm and assistance over the last 4 years. It is only on reflection that I appreciate how he kept this work on track, whilst encouraging me to explore my own ideas and how doing so has enhanced the quality of the work presented here. Drs. Andrew Kirk and Geoff Fishpool also deserve special thanks for their guidance, and above all, their understanding in the final months of this work. I also owe great thanks to...

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Section: Thermoelectric Currentssupporting

confidence: 90%

Characterisation of detached plasmas on the MAST tokamak

Harrison

2011

Journal of Nuclear Materials

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“…EFIT uses a tension spline model [20] to parameterize the p ′ (ψ) and f f ′ (ψ) source profiles whereas CLISTE uses cubic splines with curvature regularization. Unlike EFIT, source profiles routinely extend to open field lines in the SOL where they can be constrained using pressure data and shunt resistance measurements of poloidal currents flowing through tiles in the axisymmetric divertor [21]. Constant pressure and force balance is assumed to hold along open fieldlines until a vessel structure is encountered whereupon the plasma current density and pressure fall to zero across one grid interval.…”

Section: Edge Current Identifiability Using the Cliste Equilibrium Codementioning

confidence: 99%

Identification of edge-localized moments of the current density profile in a tokamak equilibrium from external magnetic measurements

Carthy¹

2011

Plasma Phys. Control. Fusion

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Abstract.The flux surface topology of a toroidal plasma bounded by a magnetic separatrix allows edge moments of the toroidal current density profile to be identified in an MHD equilibrium reconstruction code using only external magnetic measurements. This is demonstrated analytically for simple plasma shapes and applied to experimental data on the ASDEX Upgrade tokamak where CLISTE reconstructions from magnetic data are shown to be consistent with those obtained from a more complete set of diagnostic data. An independent demonstration of edge current profile recoverability is obtained by analyzing the reconstruction errors for a database of Monte Carlogenerated equilibria.

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“…The net target current integrated over the lower divertor tile is measured by shunts [37] and shown in figure 8. The spatial extent of the measurement is up to ds sep 0.15 m and corresponds to the region where Langmuir probe and thermography data are available and integrated to obtain total ELM energies and ion fluxes.…”

Section: Electric Current and Sheath Potentialmentioning

confidence: 99%

Divertor power and particle fluxes between and during type-I ELMs in the ASDEX Upgrade

et al. 2008

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Abstract. Particle, electric charge and power fluxes for type-I ELMy H-modes are measured in the divertor of the ASDEX Upgrade tokamak by triple Langmuir probes, shunts, IR-thermography and spectroscopy. The discharges are in the medium to high density range, resulting in predominantly convective ELMs with moderate fractional stored energy losses of 2 % or below. Time resolved data over ELM cycles are obtained by coherent averaging of typically one hundred similar ELMs, spatial profiles from the flush-mounted Langmuir probes are obtained by strike point sweeps. Application of simple physics models is used to compare different diagnostics and to make consistency checks, e.g. the standard sheath model applied to the Langmuir probes yields power fluxes which are compared to the thermographic measurements. In between ELMs, Langmuir probe and thermography power loads appear consistent in the outer divertor, taking into account additional load due to radiation and charge exchange neutrals measured by thermography. The inner divertor is completely detached and no significant power flow by charged particles is measured. During ELMs, quite similar power flux profiles are found in the outer divertor by thermography and probes, albeit larger uncertainties in Langmuir probe evaluation during ELMs have to be taken into account. In the inner divertor, ELM power fluxes from thermography are a factor 10 larger than those derived from probes using the standard sheath model. This deviation is too large to be caused by deficiencies of probe analysis. The total ELM energy deposition from IR is about a factor 2 higher in the inner compared to the outer divertor. Spectroscopic measurements suggest a quite moderate contribution of radiation to the target power load.Shunt measurements reveal a significant positive charge flow into the inner target during ELMs. The net number of elementary charges correlates well with the total core particle loss obtained from highly resolved density profiles.As a consequence, the discrepancy between probe and IR measurements is attributed to the ion power channel via a high mean impact energy of the ions at the inner target. The dominant contributing mechanism is proposed to be the directed loss of ions from the pedestal region into the inner divertor.

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Electric currents in the scrape-off layer in ASDEX Upgrade

Cited by 44 publications

References 8 publications

Characterisation of detached plasmas on the MAST tokamak

Characterisation of detached plasmas on the MAST tokamak

Identification of edge-localized moments of the current density profile in a tokamak equilibrium from external magnetic measurements

Divertor power and particle fluxes between and during type-I ELMs in the ASDEX Upgrade

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