Particle Flux Measurements Research Articles

Power and particle balance studies using an instrumented limiter system on ATF

Power and particle balance studies on the Advanced Toroidal Facility (ATF) torsatron are carried out using a rail limiter system. Both top and bottom limiters are made of graphite tile arrays, and these tiles are instrumented with thermocouples and Langmuir probes for calorimetric and particle flux measurements. Initial experimental results indicate that the limiter power loss accounts for about 12% of the total and the radiation loss for about 30% of the total; the rest of the plasma heating power appears to be going to the vessel wall. The particle flux to the limiters is also about 18%. The fractions of power and particle flux to the limiters are relatively lower than in Tokamaks because of the low edge safety factor, q approximately 1 rather than q approximately 3 as in a typical Tokamak, at the natural boundary of the ATF plasma (which results from the magnetic stellarator configuration of this currentless device). Therefore, for limiters of the same size, these fractions are about a factor of q lower in ATF than in a comparable Tokamak device.

An axial viewing photographic technique to study turbulence characteristics of particles

An axial viewing photographic technique has been developed which can study the turbulence characteristics of droplets in planes perpendicular to the direction of mean flow. The technique provides direct measurements of particle flux and provides measurements of the mean-square values of both the r- and φ-components of turbulent velocity fluctuations of the droplets. Results are given which show the influence of particle inertia on droplet turbulence for droplets injected into a fluid flowing turbulently in a pipe.

Transport and settling of organic material in a deep-sea hydrothermal plume: evidence from particle flux measurements

Results of time-series experiments using moored sediment traps to quantify the settling hydrothermal particle flux above Endeavour Ridge suggest that the oceanic effects of carbon production associated with mid-ocean ridge hydrothermal systems are not limited to the area immediately surrounding seafloor vents. We hypothesize that particulate organic material is entrained, possibly generated in, and removed from the hydrothermal plume at least 2 km from a site of active venting. More than 95% of the organic carbon collected 21 m directly above a site of hydrothermal fluid discharge has a near-bottom, chemosynthetic source. Up to 62% of the total organic carbon flux measured 100–200 m above bottom and ≈2 km northeast of the vent field (47°57.05′N, 129°06.30′W, depth ≈ 2200 m) is chemosynthetic. Despite injectionof organic carbon at plume depths, perplexing minima in the fluxes of biogenic and inorganic detrital particles are observed at plume-depth 1900 m traps. Possible explanations for the attenuated particle fluxes include removal of material from the laterally advecting plume by zooplankton feeding, biologically mediated particle breakdown, and the effect of currents on particle collection. Patterns of particle flux we observed indicate simultaneous addition and removal of organic material at plume depths (i.e. nutrient cycling), and support the hypothesis that laterally dispersing hydrothermal plumes are three-dimensional, biologically active zones in the deep sea.

Ultrapure materials for alpha particle-sensitive applications

Materials used in applications where alpha particle radiation can produce “soft” or transitory errors are commonly specified and characterized in terms of uranium and thorium content, often by glow discharge mass spectrographic analysis. Analytical results indicate that low levels of uranium and thorium do not adequately reflect the alpha flux potential of some materials, especially in cases where radioactive isotopes are not in equilibrium or where a dominant decay parent other than uranium or thorium is present. An additional characterization technique—highly sensitive, surface alpha particle flux measurement—has been developed. Alpha particle counting, when used in conjunction with trace metal analysis, allows more optimum selection of low-alpha-radiation materials.

The prediction of swirl burner pulverised coal flames

This paper describes a validation study effected on a computational procedure for the prediction of pulverised coal combustion. Some of the essential modelling elements of the procedure are shared by other contemporary codes. Previous validation studies have for the most part been restricted to the far field of combustors fired by zero- or low-swirl number burners. These studies have been hampered by data which is not only scarce but which have frequently not been amassed with the special needs of code validation in mind. The present study relies on data collected in this laboratory which, although limited because of the difficulty of measurement in PF flames, have code validation as their primary purpose. The swirl number of 0.78 is for the most part higher than those of past studies and it is typical of industry practice. The near-burner field, all important to emissions and flame stability performance, is empathized. The quality of the gas temperature and concentration predictions for these more demanding circumstances is, while acceptable for some purposes, less than notable. It is concluded that the analytical development of PF combustion predictive codes has now outstripped the parallel demand for their step by step validation, at least as far as the near field of a typically operated, swirl burner is concerned. The search for the source of the predictive difficiency is seriously impeded by the current inability to make reliable two phase velocity measurements in fully turbulent and real burner flames. It appears that the simulation of the particle response to the mean and fluctuating gas field is less than satisfactory. Some two phase data for small scale, but turbulent, inert flows exist which have not been fully exploited. Measurements of simultaneous char particle fluxes and burnouts and of char particle residence times are feasible but scarce, they should be indulged in the next phase of validation effort.

The Measurements of Thermophoretic Deposition of Aerosol Particles in the Continuum and Slip Flow Regions

The thermophoretic deposition of limestone particles onto a cold plate above which a temperature gradient was established has been measured. The experimental setup and methodology are described. The particle size distribution was measured by means of an Andersen impactor. The concentration of particles of different sizes was also measured. The Knudsen numbers (Kn) covered both continuum and slip flow regimes (Kn = 1 × 10-2 to 0.93). The theoretical expressions for thermal velocity of particles in the two regimes were calculated using the theories of Derjaguin and Yalamow and Brock, respectively. The measured concentration of particles of each size (0.4 - 9 /μm) along with theoretical values of thermal velocity were used to predict the total particle flux. The comparison between the directly measured particle flux and the predicted values showed good agreement. This result validates the thermophoresis theoretical expressions which have been proposed for both flow regimes involved in the present investigation.

Coherent mesoscale convection patterns during northward interplanetary magnetic field

All‐sky imaging photometer (ASIP) and coincident DE 2 satellite plasma drift and particle data have been combined to study polar ionospheric convection in the presence of subvisual intensity, soft‐particle excited (F region), 6300‐Å, Sun‐aligned polar cap arcs. Coincident DE‐B drift meter data identify these arcs electrodynamically as lines of negative electric field divergence. Based on conductivities, derived from the DE‐B (low‐altitude plasma instrument) measured particle fluxes, and the measured electric field gradients, the divergence of horizontal current across these particle impact excited arcs is in good quantitative agreement with upward Birkeland currents carried by the measured particle fluxes. Although velocity structure can be found without arcs, given the ASIP identified condition of stable weak (hundreds of rayleighs) 6300‐Å Sun‐aligned arcs in the polar cap, electric field negative divergence is consistently found. These arcs (of the order of 100 km in width) are found by ASIPs in the polar cap about half the time under Bz ≥ 0 interplanetary magnetic field conditions. They are regularly seen by ASIP data to extend 1000 to over 2000 km in the sunward direction, and to persist in time often for over an hour. We are thus led to conclude that velocity gradients of this noon‐midnight elongated scale are typical of Bz ≥ 0 conditions. We further conclude that combined polar ASIP images and electrostatic potentials calculated along transpolar satellite tracks offer a valuable diagnostic for polar ionospheric convection studies under Bz ≥ 0 conditions. The ASIP time continuous two dimensionality and the satellite equipotential scaling allow individual “snapshots” of these polar convection boundaries. Application here demonstrates highly anisotropic temporally stable convection with greater order than has previously been suspected.

The Measurement of Oceanic Particle Flux—Are "Swimmers" a Problem?

The Measurement of Oceanic Particle Flux—Are "Swimmers" a Problem?

Surface analysis in fusion devices

Fusion devices with magnetic confinement of a hot plasma show a considerable amount of interaction of the plasma with material wall surfaces. This interaction strongly influences, for example, the plasma behavior due to recycling of the discharge gas (hydrogen isotopes) and release of impurity atoms from the wall surfaces. In order to assess the various effects caused by plasma–wall interactions, surface analysis techniques have been successfully applied. Among the problems studied are wall conditioning, erosion, and redeposition of material in the discharge vessel, erosion mechanisms such as sputtering or arcing, and measurement of particle fluxes into and out of the plasma by using surface probes. A variety of surface analysis techniques is used in these investigations: Rutherford backscattering, nuclear reaction analysis, proton- and electron-induced x rays, Auger electron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, etc. Some achievements and problems of surface analysis in fusion devices are outlined and illustrated by a number of examples from tokamak experiments.

Particle flux measurements with pump limiters

The pressure buildup in pump limiters is a function of the incident particle flux, the pump limiter geometry, particle-surface interactions, and effects due to interactions of the neutral gas with the incoming plasma. At sufficiently low density and for a short pump limiter throat, the pressure observed in the pump limiter chamber is a direct measure of the particle flux at the limiter slot. This paper discusses a simple model for the correlation between particle flux and pump limiter pressure in ISX-B. In addition, some estimates are presented on the thermalizaton of fast neutrals in the pump limiter duct and its implications for “enhanced particle collection.”.

Observation of impurity accumulation and concurrent impurity influx in PBX

Impurity studies in L- and H-mode discharges in PBX have shown that both types of discharges can evolve into either an impurity accumulative or nonaccumulative case. In a typical accumulative discharge, Z eff peaks in the center to values of about 5. The central metallic densities can be high, n met / n e ≈ 0.01, resulting in central radiated power densities in excess of 1 W/cm 3, consistent with bolometric estimates. The radial profiles of metals obtained independently from the line radiation in the soft X-ray and the VUV regions are very peaked. Concurrent with the peaking, an increase in the impurity influx coming from the edge of the plasma is observed. At the beginning of the accumulation phase the inward particle flux for titanium has values of 6 × 10 10 and 10 × 10 10 particles/ cm 2 s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3 × 10 12 and 1 × 10 12 particles/ cm 2 s. This increased flux is mainly due to influx from the edge of the plasma and to a lesser extent due to increased convective transport. Using the measured particle flux, an estimate of the diffusion coefficient D and the convective velocity ν is obtained.

Measurement of punch-through particle fluxes from a 200 cm long beam dump hit by a 300 GeV/c pion beam

We present a measurement of the particle flux punching through tungsten and iron beam dumps; the NA3 spectrometer was used. Momentum spectra and spatial distributions were determined for pions above GeV/c and for strange particles (K±, Ks0, Λ, Ξ; 15 < p < 50 GeV/c). Information on the effective attenuation length for strange particles was obtained by comparing the results from dumps of different lengths (200 and 220 cm).

A thin-film bolometer for particle current measurements

Design and performance of a Ge thin film bolometer is described. The device is used for measurement of neutral charged particle fluxes in the low keV range. It has an active area of 7 mm2 and a total thickness of about 25 mu m. It can be operated at room temperature and is compatible with vacua of 10-8 Torr. The detection limit for heavy particle beams is of the order of 5 mu W or 70 mu W cm-2 respectively, corresponding to a temperature increase of about 0.05 degrees C.

Energy Selecting Action of Limiters on Particle Fluxes Penetrating into the SOL‐Plasma

AbstractA simple model of the penetration of particle effluxes from the core plasma into the SOL‐plasma of tokamaks is proposed. The assumptions made are free streaming of particles parallel to the magnetic field and anomalous particle transport perpendicular to the toroidal field with a constant radial velocity. The model has been proved for measured particle fluxes of Li which was injected into the core plasma of the tokamak T‐10. The dependence of the Li‐particle flux on the minor radius as well as toroidal asymmetries in the SOL‐plasma can be explained by the results of the calculations.

Surface probe measurements of impurities and hydrogen isotopes in the Heliotron E device

Particle flux measurements in the divertor region of the Heliotron E helical system were performed during currentless plasma discharges. A rotatable amorphous silicon probe was utilized to measure retained deuterium by NRA and titanium by AES. An isotopic exchange experiment revealed that gas release from wall surfaces did not change the composition of plasma during discharges. The particle flux at the probe surface was found to be almost a linear function of plasma density.

Space/time statistics of the turbulence in a tokamak edge plasma

The results of a study of the statistical space/time properties of the turbulence observed in the edge region of the Pretext tokamak are reported. A local estimate of the wavenumber frequency spectra S(κ,ω) for poloidal (ky)an d toroidal (kz) wavenumbers is determined for the range 0.5 cm−1 < k < 7.5 cm−1, for both potential and density fluctuations obtained from spatially fixed Langmuir probe pairs. The S(ky, ω) spectra aredominated by low frequencies ( < 200 kHz) and small wavenumbers (< 3 cm−1) and appear broadened about an approximately linear statistical dispersion relation, k̄(ω). The broadening is characterized by a spectral width σk (ω) (root-mean-square deviation about k̄(ω)) which is of the order of k̄(ω). The turbulence appears to propagate poloidally with an apparent mean phase velocity of (1–2) × 105 cm·s−1 in the ion diamagnetic drift direction. Measurements of the fluctuation-induced particle transport reveal the particle flux to be outward and resulting primarily from the low-frequency, long-wavelength components of the turbulence. A particle diffusion coefficient Dx, estimated from the measured particle flux and density profiles, is of the order of the coefficient estimated for Bohm diffusion, but appears to increase with density.

Particle and heat flux measurements in PDX edge plasmas

This paper describes the use of novel combined Langmuir-calorimeter probes to measure edge plasma conditions near the midplane in PDX. The probes consisted of up to five Langmuir probes and up to two calorimeters. Single and double probe characteristics yield n e and T c which are compared with results derived from a triple probe analysis. The calorimeters measure heat flux in the electron and ion drift directions. This paper presents time-resolved radial profiles of n e , T e , V F (floating potential),and P (heat flux) during high power neutral beam-heated, single-null discharges and circular scoop limiter discharges. The temporal dependence of these quantities displays the previously observed behavior with respect to gross discharge characteristics; however, an additional dependence on confinement mode has been observed. During the H-mode of energy confinement, a transient depression of n e , T e , and P occur in the scrape-off plasma.

Windblown sand on Venus: Preliminary results of laboratory simulations

Small particles and winds of sufficient strength to move them have been detected from Venera and Pioneer-Venus data and suggest the existence of aeolian processes on Venus. The Venus wind tunnel (VWT) was fabricated in order to investigate the behavior of windblown particles in a simulated Venusian environment. Preliminary results show that sand-size material is readily entrained at the wind speeds detected on Venus and that saltating grains achieve velocities closely matching those of the wind. Measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from Martian and terrestial simulations. Results are in general agreement with theory, although certain discrepancies are apparent which may be attributed to experimental and/or theoretical-modeling procedures. Present findings enable a better understanding of Venusian surface processes and suggest that aeolian processes are important in the geological evolution of Venus.

Interpretation of eddy-correlation measurements of particulate deposition and aerosol flux

Eddy correlation measurement of aerosol particle fluxes has recently become feasible with the advent of fast response particle measurement devices such as multichannel spectrometers based on optical scattering, nephelometers and electrical charge devices. Preliminary work in this area has identified several problems in data interpretation. Those investigated in this paper are: (1) particle equilibrium with ambient relative humidity, (2) errors caused by humidity fluctuations, (3) errors caused by horizontal wind fluctuations and (4) statistical validity of the data. Consideration of evaporation response time indicates that particles with radius less than roughly 1.0 μm are continually in equilibrium, but that when the environment is nearly saturated, equilibrium is a strong function of relative humidity. Errors in the vertical particle flux caused by humidity fluctuations are shown to be proportional to the saturation ratio flux, w′ S′. Over the ocean, this can lead to an apparent upward particle flux near the surface which when characterized by a dry deposition velocity, v d , is on the order of c 1 2 d u ∗ . An analysis of the statistical properties of particle-covariance averages indicates that the minimum uncertainty in dry deposition velocity is of the order of σ w / trN where σ 2 w is the vertical variance and N the total number of particles used to obtain v d .

The characteristics of the ion and neutral fluxes incident on the substrate in an ion plating discharge

In order to understand the processes occurring during ion plating the energy distribution of the particles impinging on the cathode must be known and an experimental system capable of monitoring the energy and mass distribution of the ionized and neutral particle fluxes leaving the discharge region through a pin-hole in the cathode is described. The system comprises an extraction/collimation arrangement followed by deflectors and electron bombardment ionizer, a retarding lens-hemispherical electrostatic analyser and a quadrupole mass analyser. The transmission characteristics of the complete optical system are described and the implications of the measured particle flux characteristics are discussed in terms of the physical processes, e.g. ion beam mixing, gas build-up, deposition and sputtering which occur during plating.