Nonlocal Heat Transport Due to Steep Temperature Gradients

Luciani, J. F.; Mora, P.; Virmont, J.

doi:10.1103/physrevlett.51.1664

Cited by 422 publications

(236 citation statements)

References 21 publications

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“…Luciani, Mora & Virmont 1983;Albritton et al 1986;Krasheninnikov 1993;Kukushkin & Runov 1994;Manheimer, Colombant & Goncharov 2008). However, in practice only the simple, so-called 'flux-limited' expression for the parallel heat flux, which can be traced back to Krall & Trivelpiece (1973), is routinely used in the 2-D edge plasma transport codes:…”

Section: Equations For Plasma Transport In the 2-d Codesmentioning

confidence: 99%

Physics of ultimate detachment of a tokamak divertor plasma

Krasheninnikov¹,

2017

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The basic physics of the processes playing the most important role in divertor plasma detachment is reviewed. The models used in the two-dimensional edge plasma transport codes that are widely used to address different issues of the edge plasma physics and to simulate the experimental data, as well as the numerical schemes and convergence issues, are described. The processes leading to ultimate divertor plasma detachment, the transition to and the stability of the detached regime, as well as the impact of the magnetic configuration and divertor geometry on detachment, are considered. A consistent, integral physical picture of ultimate detachment of a tokamak divertor plasma is developed.

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Section: Equations For Plasma Transport In the 2-d Codesmentioning

confidence: 99%

Physics of ultimate detachment of a tokamak divertor plasma

Krasheninnikov¹,

2017

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“…However, laboratory experiments and numerical studies have shown that the actual conductivity is smaller than that given by 5 Clearly here we are not dealing with a pure hydrogen plasma. Spitzer when the temperature variation length scale L $ 10 9 cm is less than 30 times longer than the mean free path of the thermal electrons k ¼ 1:4 ; 10 8 (T /10 7 K) 2 (n/10 10 cm À3 ) À1 cm (Luciani et al 1983;Post 1956). This is the case for typical solar flare conditions.…”

Section: Cooling Processes: Theory Versus Observationmentioning

confidence: 99%

Evolution of the Loop‐Top Source of Solar Flares: Heating and Cooling Processes

Jiang

Liu

et al. 2006

ApJ

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We present a study of the spatial and spectral evolution of the loop-top (LT) sources in a sample of six flares near the solar limb observed by RHESSI. A distinct coronal source, which we identify as the LT source, was seen in each of these flares from the early ''preheating'' phase through the late decay phase. Spectral analyses reveal an evident steep power-law component in the preheating and impulsive phases, suggesting that the particle acceleration starts upon the onset of the flares. In the late decay phase the LT source has a thermal spectrum and appears to be confined within a small region near the top of the flare loop and does not spread throughout the loop, as is observed at lower energies. The total energy of this source decreases usually faster than expected from the radiative cooling but much slower than that due to the classical Spitzer conductive cooling along the flare loop. These results indicate the presence of a distinct LT region, where the thermal conductivity is suppressed significantly and/or there is a continuous energy input. We suggest that plasma wave turbulence could play important roles in both heating the plasma and suppressing the conduction during the decay phase of solar flares. With a simple quasi-steady loop model we show that the energy input in the gradual phase can be comparable to that in the impulsive phase and demonstrate how the observed cooling and confinement of the LT source can be used to constrain the wave-particle interaction.

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“…Laboratory experiments and numerical studies showed that the actual conductivity is smaller (by at least a factor of two) than that given by Spitzer when L T 30λ (e.g. Luciani et al 1983). This is the case for typical solar flare loops with higher temperature (T ) because λ increases with T 2 .…”

Section: Introductionmentioning

confidence: 90%

Evidence of thermal conduction suppression in hot coronal loops: supplementary results

et al. 2015

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Abstract. Slow magnetoacoustic waves were first detected in hot (>6 MK) flare loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe xix and Fe xxi lines. Recently, such longitudinal waves have been found by SDO/AIA in the 94 and 131Å channels. Wang et al. (2015) reported the first AIA event revealing signatures in agreement with a fundamental standing slow-mode wave, and found quantitative evidence for thermal conduction suppression from the temperature and density perturbations in the hot loop plasma of 9 MK. The present study extends the work of Wang et al. (2015) by using an alternative approach. We determine the polytropic index directly based on the polytropic assumption instead of invoking the linear approximation. The same results are obtained as in the linear approximation, indicating that the nonlinearity effect is negligible. We find that the flare loop cools slower (by a factor of 2-4) than expected from the classical Spitzer conductive cooling, approximately consistent with the result of conduction suppression obtained from the wave analysis. The modified Spitzer cooling timescales based on the nonlocal conduction approximation are consistent with the observed, suggesting that nonlocal conduction may account for the observed conduction suppression in this event. In addition, the conduction suppression mechanism predicts that larger flares may tend to be hotter than expected by the EM-T relation derived by Shibata & Yokoyama (2002).

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Nonlocal Heat Transport Due to Steep Temperature Gradients

Cited by 422 publications

References 21 publications

Physics of ultimate detachment of a tokamak divertor plasma

Physics of ultimate detachment of a tokamak divertor plasma

Evolution of the Loop‐Top Source of Solar Flares: Heating and Cooling Processes

Evidence of thermal conduction suppression in hot coronal loops: supplementary results

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