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Elutriation is an efficient process for extracting microplastics. The development of a numerical model has shown the need for optimizing aspects of the design of the actual elutriation protocol as well as the dimensioning of the column to increase its efficiency. The study aims to propose new dimensioning data and protocol elements for designing an efficient column. Using a numerical model, the filling velocity was calculated as a function of the size and the density of the particles to prevent sand suspension. The sieving protocol was adapted to increase the density limit for the extraction of plastic particles from 1460 to >1800 kg·m−3. The durations of the elutriation and the column height were calculated to improve the control of the particle suspension. These results contribute to the development of the next generation of elutriation system and will accelerate the study of plasticome in the context of sandy sediments.

The sediment transport phenomenon is considered to be an important factor in improving coastline hydraulic performance. This research studied the effects of long waves as simulated solitary waves on the sediment transport to estimate the sediment transport rate in different coastal forest cover (CFC) densities. To examine how trees altered the wave characteristics, artificial trees were used experimentally to simulate the aligned and staggered configurations in totally 32 cover densities and 3 different wave heights. Results revealed that the CFC could averagely reduce the total sediment transport rate by up to 41.18% (in the densest case by 54% and 45% in staggered and aligned configurations, respectively, compared with the no-CFC case). The optimum density limit with maximum reduction effect was determined as 40–50% for the staggered and 70–80% for the aligned pattern. The configuration effects on the CFC efficiency were also investigated and showed the superiority of the zigzag configuration over the aligned arrangement. This study also used the laboratory data to develop two equations for calculating the sediment transport rate in the presence of coastal cover.

In FTU, the density profile in the presence of large MARFE becomes more and more peaked with increasing density, forming strong density gradients close to the radial region affected by the MARFE. The temperature at the edge drops to few eV, driving a drop of the whole profile. The estimated particle source cannot justify the change of the density gradient, which instead is well-explained by a change of the pinch. A thermo-diffusion term well-describes the pinch evolution and the experimental behavior of the density at those radii where temperature measurements are reliable.

A revised formulation of the perpendicular diffusive transport model in 2D multi-fluid edge codes is proposed. Based on theoretical predictions and experimental observations a dependence on collisionality is introduced into the transport model of EDGE2D–EIRENE. The impact on time-dependent JET gas fuelled ramp-up scenario modelling of the full transient from attached divertor into the high-recycling regime, following a target flux roll over into divertor detachment, ultimately ending in a density limit is presented. A strong dependence on divertor geometry is observed which can mask features of the new transport model: a smoothly decaying target recycling flux roll over, an asymmetric drop of temperature and pressure along the field lines as well as macroscopic power dependent plasma oscillations near the density limit which had been previously observed also experimentally. The latter effect is strongest for scenarios with strike points on vertical targets and vanishes in case of asymmetric divertor configurations.

This study demonstrates that any temperature dependency introduced in the term describing the inter-molecular repulsive forces of analytical EOS models leads to prediction of the infinite value for the isochoric heat capacity at the density limit conditions. The temperature-dependent hard sphere diameters and co-volumes necessarily result in the non-physical negative infinite values of this property at the infinite pressure, which in turn leads to the non-physical predictions of other properties, such as the sound velocities. In addition, this study demonstrates that the inconsistency existing at the imaginary state of infinite pressure may have a very strong negative impact on predicting the data of real fluids at the experimentally available pressures. Therefore making the repulsion compressibility factor temperature-dependent seems highly non-recommended.

A moveable graphite limiter has been developed in order to investigate the influence of the horizontal plasma position on the density limit in the HT-7 tokamak. The local recycling and density limit behaviour has been studied in this Letter, which shows that if plasma is shifted outwards the recycling is low, for inwards shift is high. For these set of ohmic discharges a maximum Greenwald number, N GW > 1.2 , was achieved, when the plasma column was repositioned more than Δ / / = + 2.25 cm outwards. It is important that lower local recycling discharge leads lower radiation power and higher density.

Application testing of the low activation ferritic steel to plasma is in progress in the JFT-2M tokamak. The toroidal field ripple reduction with ferritic insertion between the vacuum vessel and the toroidal field coils (1st stage) was successfully demonstrated. So far, no deteriorating effects of ferritic boards (FBs) inside the vacuum vessel has been observed in the pre-testing on compatibility with plasma (2nd stage). The density limit was improved by more than a factor of 1.6 after boronization with inside FBs. Design and preparation works are in progress for the testing on compatibility with plasma (3rd stage), where inside wall of the vacuum vessel will be fully covered with ferritic steel.

3D modeling on W7-AS suggests that to obtain divertor plasma detachment, upstream separatrix densities nes in the range of 10 20 m −3 will be necessary. This paper investigates the ratio of nes to the line-averaged density n e under a variety of conditions – P heat ∼0.4–2 MW , n e ∼0.2–2.7×10 20 m −3 – for inner-limiter plasma configurations in preparation for the upcoming divertor phase. n es / n e ranges from 0.05 for the quiescent H-mode H* (Pecrh∼0.4 MW) up to ∼0.35 for high-power (Pnbi∼2 MW), heavily fueled discharges where nes approaches 1020 m−3 within a density ramp. For P nbi MW , n es / n e declines with increasing n e as the H-mode threshold density n e thr approaches. L–H–L switching transitions cause n es / n e to alternate between higher and lower values. The attainment of H* implies reduced n es / n e and incipient radiation collapse of the core plasma. n e thr and n es / n e both increase with heating power by which means detachment-relevant nes can be attained, albeit at n e close to the density limit. These phenomena in detail exhibit a sensitive dependence on ιa – even a 1% change results in evident and reproducible plasma behavior.

The systematic change of a resonance state with high momenta is studied with increasing particle density in the 2D attractive Hubbard model. Within the conserving self-consistent T-matrix approximation, we present the spectral functions for the one and two particle Green's functions as well as the self-energy. In the small density limit, the resonant state becomes stable and the result from the self-consistent calculations shows a good agreement with that from a simple analytical calculation. As particle density is increased, the resonance state acquires a short lifetime due to the increasing decay into two free particles.

We have studied the processes limiting plasma density and successfully achieved discharges with density ∼50% above the empirical Greenwald scaling with H-mode energy confinement. This was accomplished by density profile control, enabled through pellet injection and divertor pumping. Several density-limiting mechanisms, including MARFEs and pellet loss processes, were successfully avoided. Finally we have looked in detail at the first and most common density limit process in DIII-D, total divertor detachment, and found that the local upstream separatrix density n sep, det e at detachment onset (partial detachment) increases with the scrape-off layer heating power, Pheat, i.e. nsep,dete∼P0.8heat. This is in marked contrast to the line-average density at detachment which is insensitive to the heating power. Our data are in reasonable agreement with the Borass model, which predicted that the upstream density at detachment would increase as P0.7heat.

This paper describes the confinement characteristics of high density Elmy H-modes obtained in the JET Mark I experimental campaign. Plasma pulses carried out with and without the in-vessel cryopump operational (≈ 240 m3 s−1 pumping speed for deuterium) are compared. In all cases, it is found that the H-mode density limit is not disruptive, but manifests itself as a loss of confinement, accompanied by an increase of neutral pressure at the plasma edge. The interpretation of the H-mode density limit in terms of the Greenwald scaling is discussed. It is also shown that the loss of confinement correlates to the onset of detachment in the divertor, and that operation at high density in H-mode is compatible with partial detachment but not with full detachment.

The density limit is increased by the application of an external helical field in the JFT-2M tokamak. The effect of the magnetic stochasticity due to the external field is investigated to study the mechanism of the improved density limit related to the edge plasma behaviour. The improvement is correlated with the retardation of the increase in the plasma inductance. At the improved density limit, local radiation loss is modified by the helical field, in which that from the vicinity of separatrix X-point is remarkably reduced, while that from outboard edge is slightly increased. The formation of a positive radial electric field at the plasma edge is also observed in the presence of the helical field.

We have studied space-charge effects in low-energy proton synchrotrons using a simulation code developed specifically for supercomputers. The tracking of the beam with a few thousand macro particles is completely self-consistent, thus making it possible to follow the charge distribution as well as the beam size as a function of time. A proper substitution of the kick for the continuous space-charge force has been considered. The simulation is performed for a model lattice (similar to the SSC low energy booster) with and without half-integer resonances. In the lattice with the resonances, the rms emittance growth often observed in experiments occurs and the phase space density limit appears. The limiting value is, however, not directly related to the Laslett formula as expected. If we look at individual particles, there is a bare tune region where the real tune of some particles modified by space charge is within the resonance width. In the lattice without half-integer resonances, the rms emittance growth also occurs. It is associated with higher-order resonances driven by the beam itself. Only the tail of the beam is affected by the resonance, and the phase space density at the core remains almost unchanged.

We study the plasma phase of the two-dimensional Coulomb gas in the small density limit. The analysis is done using the correspondence of the Coulomb gas with the 1 + 1 sine-Gordon model, which has been exactly solved by the quantum inverse method. We construct the correct vacuum of the field theory, improving the former results. We obtain exact results for the Coulomb gas, which confirm the previous perturbative calculations.

Pressure-induced densification and crystallization of vapor-deposited amorphous Se, As, Ge and GeTe were investigated. In general, the density of the amorphous material increases monotonically with pressure and crystallization occurs after a certain pressure level is reached. For each amorphous material there appears to exist an upper density limit beyond which crystallization occurs. The pressure effect on individual substances is correlated to their short-range order and basic structural character.

By doing a formal series expansion of the partition function in terms of the inverse of the chemical potential associated with baryon number conservation, μ, it is shown that the dominant terms for large baryon density correspond to the Hartree, or mean-field, approximation.

The problem of the detection of erroneous data has led us to define the ‘doubtful patients’ as patients who have a small density. Our program DOUBT computes the densities associated with each patient by using the method of n nearest neighbors. Then the program allows us to define a density limit, and chooses the patients who have a smaller density then the doubtful patients. The remaining patients may be classified by the program.

A pump limiter is applied to the JFT-2M tokamak in order to reduce edge gas buildup. About 12% of the effective loss flux is removed by the pump limiter and the fueling efficiency is improved by 30%. In the high density regime, the gas buildup is successfully reduced and edge cooling by cold gas-puffing is prevented by the pump limiter. The pump limiter also improves the density limit and the energy confinement time. Improvement in the nτ value is about 34%. This pump limiter is shown to be compatible with the limiter H-mode.

We compare eight possible definitions of the surface thickness for two density profiles. One definition is eliminated, and then the 10–90 thickness t is shown to be in satisfactory agreement with the other six. Our earlier work on the liquid-vapour interface is taken further, with a physical interpretation of the slowly varying density limit for the surface energy ∈; an improved estimate of t using experimental values of ∈ and the bulk energy; and an estimate of t using experimental values of ∈ and the surface tension. We obtain t ≈ 1.3d (d is the atomic diameter) for Ar, Kr and Xe near their triple points. A comparison is made with other estimates for t/d. These vary from 1 to above 3. Our results are in best agreement with Monte-Carlo simulations of the interface. The results for liquid 4He at zero temperature are discussed briefly.

Recent laboratory experimental evidence concerning the photometric properties of the lunar surface materials, as well as the Surveyor I photographs, have thrown considerable doubt on the highly underdense, “fairy castle” model of the uppermost lunar surface layer. Laboratory tests of the density of rock powders in various size ranges sifted in ultra-high vacuum, indicate a probable upper density limit of about 1.5 gm/cc for the bulk of the lunar surface material. The importance of grain shape in controlling density is shown, and a figure of about 1.0 gm/cc is arrived at as a likely lunar density to be used in calculations of bearing strength, thermal conductivity, and dielectric constant.

The main results of computer simulations of lower hybrid current drive (LHCD) in tokamaks including the parasitic part of the wave spectrum and runaways are presented. The importance of the short-wavelength part of the spectrum for the radial profile of the driven current is shown. An explanation of the density limit of LHCD is suggested.

Experimental Faraday effect data of Ingersoll and Liebenberg for the inert gases helium, neon, argon, krypton and xenon are re-evaluated. From the data for helium a direct calculation of the atomic polarizability at the zero frequency, density limit is obtained and compared with recent discussions. Anomalies exhibited by the neon data are discussed.