On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

On the experimental data processing of magnetoresistance oscillations in two-dimensional electron gas

A new method for processing data on the Shubnikov-de Haas effect in quasi-two-dimensional systems is suggeste

On the experimental data processing of magnetoresistance oscillations in two-dimensional electron gas

A new method for processing data on the Shubnikov-de Haas effect in quasi-two-dimensional systems is suggeste

On the experimental data processing of magnetoresistance oscillations in two-dimensional electron gas

A new method for processing data on the Shubnikov-de Haas effect in quasi-two-dimensional systems is suggeste

Effect of partial ordering of a two-dimensional system of scatterers on the anisotropy of its kinetic coefficients

The effect of partial ordering of impurities (correlated along one direction and uncorrelated along the other) on the kinetic coefficients is considered. It is shown that the geometry of the spatial impurity distribution by itself has no effect on the diffusion coefficient or conductivity for scattering by a spherically symmetric potential, and these coefficients remain the same as for an uncorrelated system of impurities

Spatial distribution of a hole localized on acceptor in deformed crystal

The influence of the host-crystal deformation on the acceptor wave-function in a cubic crystal isconsidered. The calculations are based on the numerical solution of the Luttinger Hamiltonian for a holein a complex valence band. The deformation is taken into account using Bir-Pikus Hamiltonian for thedeformation. The results can be used for the interpretation of the STM images in strained cubic crystals

Warping a single Mn acceptor wavefunction by straining the GaAs host

Transition-metal dopants such as Mn determine the ferromagnetism in dilute magnetic semiconductors such as Ga1-xMnxAs. Recently, the acceptor states of Mn dopants in GaAs were found to be highly anisotropic owing to the symmetry of the host crystal. Here, we show how the shape of such a state can be modified by local strain. The Mn acceptors near InAs quantum dots are mapped at room temperature by scanning tunnelling microscopy. Dramatic distortions and a reduction in the symmetry of the wavefunction of the hole bound to the Mn acceptor are observed originating from strain induced by quantum dots. Calculations of the acceptor-state wavefunction in the presence of strain, within a tight-binding model and within an effective-mass model, agree with the experimentally observed shape. The magnetic easy axes of strained lightly doped Ga1-xMnxAs can be explained on the basis of the observed local density of states for the single Mn spi