Systematic errors in tokamak magnetic equilibrium reconstruction: a study of EFIT++ at tokamak COMPASS

Jiráková, Kateřina; Kovanda, Ondřej; Adámek, Jiřı́; Komm, M.; Seidl, J.

doi:10.1088/1748-0221/14/11/c11020

Cited by 6 publications

(4 citation statements)

References 21 publications

(26 reference statements)

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“…The analysis was based on the EFIT equilibrium reconstruction and its accuracy. An investigation of COMPASS data previously reported that there is a significant uncertainty in the estimate of separatrix position [25] and an improved EFIT variant was implemented. In our datasets, the difference between the EFIT variants was minimal and it resulted in a minor change in λ q results (<10% on average).…”

Section: Discussionmentioning

confidence: 99%

Experimental evidence of very short power decay lengths in H-mode discharges in the COMPASS tokamak

Hecko,

Komm,

Sos

et al. 2023

Plasma Phys. Control. Fusion

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Analysis of the heat ﬂuxes in the scrape-oﬀ layer (SOL) plasma is important for prediction of divertor tile heat loads in future reactor-sized tokamak machines. Typically, the radial heat ﬂux proﬁle can be accurately characterized by the decay length parameter λq. The predictions are then based on the dependence of λq on plasma and machine parameters. In the recent years, several empirical scaling models were derived from a collective database of decay lengths observed in several large tokamaks as well as two spherical tokamaks. Most recently, a report from the TCV tokamak showed a deviation from several of the proposed models.[1]In this work, ∼ 100 edge plasma profiles of ELMy H-mode discharges were collected from the COMPASS tokamak database for heat flux analysis. The COMPASS tokamak has similar machine size and plasma parameters to the TCV tokamak offering a valuable comparison. The λq was measured in both the downstream and the upstream SOL utilizing a divertor probe array, an IR camera, and the Thomson scattering diagnostics. A comparison with the predictions of several scaling models indicated an occurrence of anomalously short (by a factor of 2–5) inter-ELM power decay lengths in both upstream and downstream, as well as a difference in λq between these two regions. Possible causes related to the accuracy of magnetic reconstruction were eliminated and physics-based sources of apparent compression effects were hypothesized as a motivation for future research.

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Section: Discussionmentioning

confidence: 99%

Experimental evidence of very short power decay lengths in H-mode discharges in the COMPASS tokamak

Hecko,

Komm,

Sos

et al. 2023

Plasma Phys. Control. Fusion

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“…Throughout this paper the radial profiles are plotted relatively to the last closed flux surface (LCFS). The exact position of the LCFS on COMPASS is routinely obtained by means of probes [30] or magnetic equilibrium reconstruction. In this paper we use probe measurements to locate the maximum of plasma potential, which improves the precision of the position of the LCFS compared to the one provided by the magnetic equilibrium reconstruction.…”

Section: Ion and Electron Temperature Ratio In The Solmentioning

confidence: 99%

Statistical properties of ion and electron temperature fluctuations in the edge of the COMPASS tokamak

Cipciar

Adámek

Horáček

et al. 2022

Plasma Phys. Control. Fusion

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This paper presents measurements of the plasma turbulence with an emphasis on the ion temperature fluctuations in comparison to the electron temperature and the ion saturation current fluctuations in the edge of the COMPASS tokamak. The ion temperature values are obtained by using a fast swept ball-pen probe, with temporal resolution up to 10 µs, accompanied by independent 1 µs measurements of the electron temperature and ion saturation current. The experimental results obtained for a wide range of line-averaged densities show that statistical properties of the fluctuations are in good agreement with a Beta or Gamma distribution function. In addition, the dependence of the averaged ion and electron temperatures on the line-averaged density is studied in the near and main Scrape Off Layer region.

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“…Note that only relative changes of p down /p up are relevant since the determination of separatrix location can exhibit a systematic offset [22], which influences the absolute value of p up . This is a known caveat of equilibrium reconstruction codes, which is commonly assessed by an estimation of the separatrix temperature using the 2 point model for the conductionlimited regime.…”

Section: Plasma Coolingmentioning

confidence: 99%

Power exhaust by core radiation at COMPASS tokamak

Komm¹,

Mancini

Morbey

et al. 2021

Nucl. Fusion

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Substantial power dissipation in the edge plasma is required for the safe operation of ITER and next-step fusion reactors, otherwise unmitigated heat fluxes at the divertor plasma-facing components (PFCs) would easily exceed their material limits. Traditionally, such heat flux mitigation is linked to the regime of detachment, which is characterised by a significant pressure gradient between upstream and downstream scrape-off layer (SOL). However, the physics phenomena responsible for power dissipation and pressure loss are distinctly different, especially when the power dissipation is achieved by impurity seeding. In principle, it is possible to achieve substantial mitigation of the heat fluxes while maintaining conservation of the pressure along the open field lines in the SOL. This regime can be accessed by injection of medium- or high-Z impurities, which mostly radiate inside the last closed flux surface. The critical question related to such an approach is the effect on confinement and perspective fusion power generation in future thermonuclear reactors. In this work, we report on experiments at COMPASS tokamak, where neon and argon impurities were injected in ohmic or NBI-heated low confinement plasmas. With appropriate seeding waveform, stable scenarios were achieved, avoiding the radiative collapse of plasmas. Significant reduction of heat fluxes at the outer target was observed, with heat flux pattern similar to the one previously achieved by nitrogen seeding. The reduction of downstream pressure was, however, accompanied by an equal reduction of upstream pressure, indicating that the power dissipation occurred inside the separatrix. Indeed, the impurity cooling is causing a significant drop of edge temperature; however, the effect in the plasma centre is much less pronounced.

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Systematic errors in tokamak magnetic equilibrium reconstruction: a study of EFIT++ at tokamak COMPASS

Cited by 6 publications

References 21 publications

Experimental evidence of very short power decay lengths in H-mode discharges in the COMPASS tokamak

Experimental evidence of very short power decay lengths in H-mode discharges in the COMPASS tokamak

Statistical properties of ion and electron temperature fluctuations in the edge of the COMPASS tokamak

Power exhaust by core radiation at COMPASS tokamak

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