The evidence for nonlocal transport in the Texas Experimental Tokamak

Gentle, K. W.; Bravenec, R. V.; Cima, Greg; Hallock, G. A.; Phillips, P. E.; Ross, D. W.; Rowan, W. L.; Wootton, A. J.; Crowley, T. P.; Ouroua, A.; Schoch, P. M.; Watts, Christopher

doi:10.1063/1.872255

Cited by 39 publications

(62 citation statements)

References 16 publications

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“…The most famous example of the non-local effect in electron heat transport is the inward propagation of edge cooling. The first experiment was carried out on TEXT about 20 years ago [1,2,3], in which carbon was injected into the edge plasma to induce a temperature perturbation. The edge temperature decreased rapidly as expected, but interestingly the core temperature promptly began to rise, and peaked within a few miliseconds.…”

Section: Introductionmentioning

confidence: 99%

Non-local heat transport in Alcator C-Mod ohmic L-mode plasmas

et al. 2014

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Abstract. Non-local heat transport experiments were performed in Alcator C-Mod Ohmic L-mode plasmas by inducing edge cooling with laser blow-off impurity (CaF 2 ) injection. The non-local effect, a cooling of the edge electron temperature with a rapid rise of the central electron temperature, which contradicts the assumption of "local" transport, was observed in low collisionality linear Ohmic confinement (LOC) regime plasmas. Transport analysis shows this phenomenon can be explained either by a fast drop of the core diffusivity, or the sudden appearance of a heat pinch. In high collisionality saturated Ohmic confinement (SOC) regime plasmas, the thermal transport becomes local: the central electron temperature drops on the energy confinement time scale in response to the edge cooling. Measurements from a high resolution imaging x-ray spectrometer show that the ion temperature has a similar behavior as the electron temperature in response to edge cooling, and that the transition density of non-locality correlates with the rotation reversal critical density. This connection may indicate the possible connection between thermal and momentum transport, which is also linked to a transition in turbulence dominance between trapped electron modes (TEMs) and ion temperature gradient (ITG) modes. Experiments with repetitive cold pulses in one discharge were also performed to allow Fourier analysis and to provide details of cold front propagation. These modulation experiments showed in LOC plasmas that the electron thermal transport is not purely diffusive, while in SOC the electron thermal transport is more diffusive like. Linear gyrokinetic simulations suggest the turbulence outside r/a=0.75 changes from TEM dominance in LOC plasmas to ITG mode dominance in SOC plasmas. Non-local Heat Transport in Alcator C-Mod Ohmic L-Mode Plasmas2

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Section: Introductionmentioning

confidence: 99%

Non-local heat transport in Alcator C-Mod ohmic L-mode plasmas

et al. 2014

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“…Note that the saturation level of turbulence is also affected by the level of zonal flow, as discussed in Eq. (2). So, the effect of local turbulence suppression by zonal flow is included in c NL It is necessary to examine the applicability of the simple 1D model for the analysis of complex gyrokinetic simulation data in 3D toroidal geometry.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…Also, theoretical models employing turbulence spreading may explain the challenging experimental observations of non-locality. The fast increase of core electron temperature by peripheral perturbations 2,3 can be captured by a simple two-field model with the temperature and turbulence intensity evolution. 13,14 A meso-scale model with turbulence spreading 15 shows that a H-L back transition can be triggered by the spreading of turbulence from the core region into a E r shear layer, which is consistent with the observation from recent experiments.…”

Section: Introductionmentioning

confidence: 99%

Effects of q-profile structure on turbulence spreading: A fluctuation intensity transport analysis

Kwon

Diamond

et al. 2014

Physics of Plasmas

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This paper studies effects of q-profile structure on turbulence spreading. It reports results of numerical experiments using global gyrokinetic simulations. We examine propagation of turbulence, triggered by an identical linear instability in a source region, into an adjacent, linearly stable region with variable q-profile. The numerical experiments are designed so as to separate the physics of turbulence spreading from that of linear stability. The strength of turbulence spreading is measured by the penetration depth of turbulence. Dynamics of spreading are elucidated by fluctuation intensity balance analysis, using a model intensity evolution equation which retains nonlinear diffusion and damping, and linear growth. It is found that turbulence spreading is strongly affected by magnetic shear s, but is hardly altered by the safety factor q itself. There is an optimal range of modest magnetic shear which maximizes turbulence spreading. For high to modest shear values, the spreading is enhanced by the increase of the mode correlation length with decreasing magnetic shear. However, the efficiency of spreading drops for sufficiently low magnetic shear even though the mode correlation length is comparable to that for the case of optimal magnetic shear. The reduction of spreading is attributed to the increase in time required for the requisite nonlinear mode-mode interactions. The effect of increased interaction time dominates that of increased mode correlation length. Our findings of the reduction of spreading and the increase in interaction time at weak magnetic shear are consistent with the well-known benefit of weak or reversed magnetic shear for core confinement enhancement. Weak shear is shown to promote locality, as well as stability. V C 2014 AIP Publishing LLC. [http://dx

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“…Добавим также, что введение в задачу новой сво-бодной функции, которая зависит только от координаты и входит дополнительным фактором в полные выражения для функции источника и коэффициента поглощения (см. n F в (6) и (8), и аналогичное до-полнение нужно вставить в (1) и (2)), не приводит при наложении на эту функцию условий гладкости к существенному изменению результатов и условий (5)- (8).…”

Section: ограничения физических параметров задачи и обсуждение резульunclassified

“…еще ссылки в [5,6] интерпретаций быстрого нелокального переноса). Одним из самых интересных примеров быстрого нелокального переноса является необычное направление теплового потока, а именно мгновенное в шкале диффузионного времени повышение тем-пературы в центре плазмы в случае быстрого охлаждения периферии плазмы (эксперименты cold pulse на токамаках и стеллараторах [5,6,7]) или обратный процесс -мгновенное понижение температуры в центре плазмы в случае быстрого нагрева периферии плазмы [8]. Наиболее подробный обзор экспери-ментальных данных был представлен в [7], где также предложено учесть работу сил давления (напри-мер, адиабатическое сжатие) для объяснения обсуждаемых экспериментов.…”

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A Model of Recovering the Parameters of Fast Nonlocal Heat Transport in Magnetic Fusion Plasmas

Kukushkin¹,

Kulichenko²,

Sdvizhenskii³

et al. 2017

PAST-TF

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Модель восстановления параметров быстрого нелокального переноса тепла в установках магнитного удержания. Разработана модель для интерпретации начальной стадии явления быстрого нелокального переноса, в котором отклик про-странственного профиля температуры электронов на его локальное возмущение является почти мгновенным в масштабах диф-фузионного времени, а результирующий поток тепла направлен противоположно обычной диффузии, т.е. вдоль градиента тем-пературы. Это явление наблюдается в различных установках магнитного удержания термоядерной плазмы (токамаках и стелла-раторах), но для него пока нет надёжной количественной интерпретации в рамках общепринятых моделей. Методами матема-тической оптимизации решена обратная задача восстановления ядра интегрального уравнения, описывающего нелокальный (супердиффузионный) перенос энергии, обусловленный испусканием и поглощением электромагнитных (ЭМ) волн с большой длиной свободного пробега и сильным отражением волн от стенок вакуумной камеры. Для получения решений обратной зада-чи, учитывающих погрешности экспериментальных данных, используется метод, основанный на регуляризованной (в духе не-корректных задач, используя параметрические модели) аппроксимации исходных экспериментальных данных. Разработанная расчётно-теоретическая модель использована для интерпретации экспериментов по резкому охлаждению периферийной плазмы (так называемые эксперименты «cold pulse») в стеллараторе LHD и токамаке TFTR. Показано, что для экспериментов на этих установках получены близкие результаты восстановления вида источника ЭМ-волн и коэффициента их поглощения. Процесс переноса ЭМ-волн пока рассмотрен в одногрупповом приближении, но ограничения применимости физической модели позво-ляют выделить спектральный диапазон ЭМ-волн, которые могут быть ответственны за наблюдаемое явление.Ключевые слова: нелокальный (супердиффузионный) перенос тепла, токамак, стелларатор, математическая оптимизация, электромагнитные волны. A model is elaborated for interpreting the initial stage of the fast nonlocal transport events, which exhibit immediate response, in the diffusion time scale, of the spatial profile of electron temperature to its local perturbation, while the net heat flux is directed opposite to ordinary diffusion (i.e. along the temperature gradient). Such events have been observed in various magnetic fusion devices (tokamaks, stellarators), however there is no reliable quantitative interpretation of these events in the framework of the commonly accepted models. We solve, by means of mathematical optimization methods, the inverse problem of recovering the kernel of the integral equation, which describes nonlocal (superdiffusive) transport of energy due to emission and absorption of electromagnetic (EM) waves with long free path and strong reflection from the vacuum vessel's wall. To obtain solutions of the inverse problem, which allow for the errors of experimental data, we use the method based on the regularized (in the framework of an ill-posed problem, using the parametric models) approximation of ...

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The evidence for nonlocal transport in the Texas Experimental Tokamak

Cited by 39 publications

References 16 publications

Non-local heat transport in Alcator C-Mod ohmic L-mode plasmas

Non-local heat transport in Alcator C-Mod ohmic L-mode plasmas

Effects of q-profile structure on turbulence spreading: A fluctuation intensity transport analysis

A Model of Recovering the Parameters of Fast Nonlocal Heat Transport in Magnetic Fusion Plasmas

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