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A reduced kinetic method (RKM) with a first-principles collision operator is introduced in a 1D2V planar geometry and implemented in a computationally inexpensive code to investigate non-local ion heat transport in multi-species plasmas. The RKM successfully reproduces local results for multi-species ion systems and the important features expected to arise due to non-local effects on the heat flux are captured. In addition to this, novel features associated with multi-species, as opposed to single species, cases are found. Effects of non-locality on the heat flux are investigated in mass and charge symmetric and asymmetric ion mixtures with temperature, pressure, and concentration gradients. In particular, the enthalpy flux associated with diffusion is found to be insensitive to sharp pressure and concentration gradients, increasing its significance in comparison to the conductive heat flux driven by temperature gradients in non-local scenarios. The RKM code can be used for investigating other kinetic and non-local effects in a broader plasma physics context. Due to its relatively low computational cost it can also serve as a practical non-local ion heat flux closure in hydrodynamic simulations or as a training tool for machine learning surrogates. [ABSTRACT FROM AUTHOR]

Inertial confinement fusion requires an imploded target in which a central hot spot is surrounded by a cold and dense pusher. The hot spot/pusher interface can take complicated shape in three dimensions due to hydrodynamic mix. It is also a transition region where the Knudsen and inverse Knudsen layer effect can significantly modify the fusion reactivity in comparison with the commonly used value evaluated with background Maxwellians. Here, we describe a hybrid model that couples the kinetic correction of fusion reactivity to global hydrodynamic implosion simulations. The key ingredient is a non-perturbative treatment of the tail ions in the interface region where the Gamow ion Knudsen number approaches or surpasses order unity. The accuracy of the coupling scheme is controlled by the precise criteria for matching the non-perturbative kinetic model to perturbative solutions in both configuration space and velocity space. [ABSTRACT FROM AUTHOR]

Across a transition layer of disparate plasma temperatures, the high energy tail of the plasma distribution can have appreciable deviations from the local Maxwellian distribution due to the Knudson layer effect. The Fokker-Planck equation for the tail particle population can be simplified in a series of practically useful limiting cases. The first is the approximation of background Maxwellian distribution for linearizing the collision operator. The second is the supra-thermal particle speed ordering of νTi « ν « νTe for the tail ions and νTi « νTe « ν for the tail electrons. Keeping both the collisional drag and energy scattering is essential for the collision operator to produce a Maxwellian tail distribution. The Fokker-Planck model for following the tail ion distribution for a given background plasma profile is explicitly worked out for systems of one spatial dimension, in both slab and spherical geometry. A third simplification is an expansion of the tail particle distribution using the spherical harmonics, which are eigenfunctions of the pitch angle scattering operator. This produces a set of coupled Fokker-Planck equations that contain energy-dependent spatial diffusion terms in two coordinates (position and energy), which originate from pitch angle scattering in the original Fokker-Planck equation. It is shown that the well-known diffusive Fokker-Planck model is a poor approximation of the two-mode truncation model, which itself has fundamental deficiency compared with the three-mode truncation model. The cause is the lack of even-symmetry representation in pitch dependence in the two-mode truncation model. [ABSTRACT FROM AUTHOR]

Various indications on the weakly nonlocal character of turbulent plasma transport both from experimental fluctuation measurements fromTore Supra and observations from the full-f, flux-driven gyrokinetic codeGYSELAare reported. Asimple Fisher equation model of this weakly nonlocal dynamics can be formulated in terms of an evolution equation for the turbulent entropy density, which contains the basic phenomenon of radial turbulence spreading in addition to avalanche-like dynamics via coupling to profile modulations. A derivation of this model, which contains the so-called beach effect, a diffusive and convective flux components for the flux of turbulence intensity, in addition to linear group propagation is given, starting from the drift-kinetic equation. The proposed model has the form of a transport equation for turbulence intensity, and may be considered as an addition to transport modelling. The kinetic fluxes given, can be computed using model closures, or local gyrokinetics. The model is also used in a particular setup that represents the near edge region as a relatively stable zone between the core and edge region where the energy injection is locally more substantial. It is observed that with constant, physical coefficients, the model gives a convincing qualitative profile of fluctuation intensity when the turbulence is coming from the core region with either a group velocity or a convective flux. [ABSTRACT FROM AUTHOR]

Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ∇T, but completely different edge ∇n, it may be concluded that the drive of the intrinsic rotation is the edge ∇T rather than ∇P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated., (© 2011 American Physical Society)

Previous studies demonstrated that climbing fiber activity produces a short-term increase in the responsiveness of Purkinje cells to mossy fiber inputs. This led to the hypothesis that there are concomitant alterations in the discharge of cerebellar nuclear neurons. This series of experiments was initiated to test this hypothesis in simultaneously recorded Purkinje cell-nuclear cell pairs in related regions of the cerebellar cortex and nuclei. In decerebrate cats 50 pairs of Purkinje cells and nuclear neurons were identified and simultaneously recorded during spontaneous activity and during peripheral inputs. Auto-correlograms of nuclear cell activity and cross-correlograms of the simple spike and nuclear cell activity triggered on the occurrence of spontaneous complex spikes demonstrated little correlation between these events and the discharge of nuclear neurons. To examine the effect of evoked climbing fiber inputs on the Purkinje cell simple spike and nuclear cell responses, square wave mechanical stimuli which modulated the discharge of both cells of a pair were applied to the forepaw. A separation technique was used to construct one histogram illustrating the responses of the nuclear neuron and Purkinje cell in trials in which the peripheral stimulus evoked a climbing fiber input to the Purkinje cell and another histogram showing their responses in trials in which no climbing fiber input was activated. Using this separation technique it was shown that the amplitude of most Purkinje cell responses increased by 120-1200% in trials in which climbing fiber inputs were activated. The response amplitude of 68% of the nuclear cells was modified for these pairs. Most changes in nuclear cell responses were increases ranging from 120-220%. These changes were felt to reflect the action of many Purkinje cells converging on the isolated nuclear neuron. The modulation of the nuclear neuron was not due only to the effect of the related Purkinje cell, since the gain change of the Purkinje cell and nuclear cell of each pair was not correlated (r = 0.01). The discussion of these findings emphasizes that the increased responses of the nuclear cell are most likely produced by the intracortical action of the climbing fiber system on the responsiveness of Purkinje cells to mossy fiber inputs. Climbing fiber collateral input to nuclear neurons also may contribute to the changes in the nuclear cell responses observed in these experiments.

The purpose of these experiments was to systematically examine the characteristics of the excitability change occurring after the inactivation period evoked by the climbing fiber input to Purkinje cells. Ninety-eight Purkinje cells were isolated extracellularly in unanesthetized decerebrate cats. Simple spikes and complex spikes were discriminated separately. Post-stimulus time histograms were constructed from 100 consecutive trials triggered by the occurrence of spontaneous complex spikes. Seventeen Purkinje cells exhibited a reduction of simple spike discharge rate following the inactivation period. However, 14 cells showed no change in simple spike activity, and in 67 cells the discharge rate increased. These changes in excitability following a spontaneous complex spike were independent of the tonic simple spike activity of the Purkinje cell. Single traces of spike train data from Purkinje cells showed that the change in discharge rate was variable, some complex spikes being followed by an increase and others by a decrease in activity. The basis for these observations and the differences between these data and those from studies in which the climbing fiber input was evoked by electrical olivary stimulation are discussed.

In decerebrate, unanesthetized cats, the activity of a Purkinje cell and a paired neuron in the interposed nuclei (subsequently referred to as a Purkinje cell-nuclear cell pair) were simultaneously recorded to compare their spontaneous discharge characteristics and responses to a peripheral input. Microstimulation techniques were used to determine if the two neurons were in related regions of the cerebellar cortex and interposed nuclei. First, the electrode used to record the interposed nuclear neuron was used to antidromically activate the Purkinje cell. Second, inhibitory responses with the appropriate time course were evoked in the interposed neurons with the Purkinje cell recording electrode. Both the spontaneous discharge of each pair as well as the cells' responses to a mechanically generated forepaw displacement were evaluated. A total of 35 Purkinje cell-nuclear cell pairs satisfying the microstimulation criteria were studied. During spontaneous activity there was no consistent relationship between the Purkinje cell simple spike activity and the nuclear neuron activity based on cross-correlation techniques. Auto-correlograms of both cells exhibited positive correlation for a brief time period. The variability of the interspike interval of the Purkinje cell discharge was greater than that for nuclear neurons, but there was no difference in the mean interspike interval for the pairs. The simple spike activity of Purkinje cells in response to sinusoidal displacements of the forepaw was weakly modulated. The modulation was limited to a small frequency range (2-7 Hz). In contrast the nuclear neurons exhibited a greater depth of modulation than Purkinje cells and responded to a wider range of frequencies (2-15 Hz). For many pairs of cells the relationship between the Purkinje cell and nuclear neuron discharge was not reciprocal. The responses of Purkinje cell-nuclear cell pairs to forepaw displacement were more often reciprocal to square wave than to sinusoidal stimuli. Using a technique which estimated the reciprocity of Purkinje cell and nuclear cell responses, 49% of the responses were reciprocal while 51% were not. These findings suggest that a nuclear neuron's discharge characteristics are not dominated by inputs from a single Purkinje cell and the firing relationship between a Purkinje cell and a related nuclear cell need not be reciprocal.