Collection Efficiency Measurements Research Articles

Electrohydrodynamic secondary flow and particle collection efficiency in a one-sided spike-plate type electrostatic precipitator

In this work, results of electrohydrodynamic secondary flow and particle collection efficiency measurements in an electrostatic precipitator under positive and negative voltage polarity are presented. The electrostatic precipitator had two plate collecting electrodes and a single spike discharge electrode. The spike tips were only on one side of the discharge electrode, therefore called a one-sided spike electrode. The electrohydrodynamic secondary flow pattern and collection efficiency measurements were carried out for two one-sided spike electrode positions: with the spike tips directed either upstream or downstream the primary flow. The results of the flow pattern measurement showed different flow patterns for different spike tips positions in respect to the primary flow direction. The electrostatic precipitator collection efficiency measurements clearly showed difference in the particle collection for both spike tips positions. Since the other electrostatic precipitator working parameters were the same, it can be concluded that the observed change of the electrohydrodynamic secondary flow was the main reason of the difference in the electrostatic precipitator collection efficiency.

Collection efficiency in narrow electrostatic precipitators with a longitudinal or transverse wire electrode

Recently narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application in diesel engine exhaust systems. In this work, results of particle collection efficiency measurements in narrow electrostatic precipitators for negative and positive dc voltage polarity are presented. The ESP used in this work was a parallelepiped equipped with wire discharge electrode and two collecting plate-electrodes. The experiments were carried out for two discharge electrode positions: longitudinally or transversely to the main flow direction. The obtained results showed that the collection efficiency strongly depends on the discharge electrode position. It is higher in the ESP with longitudinally-to-flow placed discharge electrode. The collection efficiency is also influenced by the EHD secondary flow generated in the ESP. The EHD secondary flow with high migration velocity (y-component of the particle velocity) and low turbulence intensity increase the chance of the particle deposition on the collecting electrodes.

Determination of the Electron Diffusion Length in Dye-Sensitized Solar Cells by Substrate Contact Patterning

A new method to estimate the electron diffusion length in dye-sensitized solar cells (DSCs) is presented. DSCs were fabricated on conducting glass substrates that were patterned by laser ablation of the fluorine-doped tin oxide coating to form parallel contact strips separated by uncontacted strips of the same width. The relative collection efficiency was measured as a function of the gap between the contact strips, which determines the lateral distance traveled by electrons to reach the contacts. To avoid complications arising from nonlinear recombination kinetics, current measurements were performed using small amplitude perturbations of the electron density close to open circuit and the maximum power point to minimize electron density gradients in the film. One and two-dimensional solutions of the continuity equation for electron transport and back reaction predict that the relative collection efficiency should fall as spacing between the contact strips exceeds the electron diffusion length and electrons are lost by back electron transfer during transit to the contacts. Measurements of the relative collection efficiency were fitted to the predicted dependence of the collection efficiency on the spacing between the contact strips to obtain the value of the electron diffusion length. The diffusion length is found to increase with voltage both at open circuit and at the maximum power point.

Characterization of proton and neutron irradiated low resistivity p-on-n magnetic Czochralski ministrip sensors and diodes

Abstract Transient Current Technique (TCT) and Charge Collection Efficiency (CCE) measurements were performed on low resistivity ( 280 Ω cm ) n-bulk, p-readout magnetic Czochralski ministrip sensors and diodes. The detectors were irradiated with neutrons and 24 GeV/ c protons up to a total NIEL equivalent fluence of 8 × 10 15 / cm 2 . The study was addressed to assess the radiation tolerance of the detectors up to fluences expected in the next generations of High Energy Physics experiments. The charge collection efficiency after irradiation was found to be much higher than for standard FZ silicon p-in-n sensors. The underlying physics of this remarkable result was investigated by performing Edge-TCT measurements on one of the neutron irradiated ministrip sensors to extract detailed informations about the field and efficiency profiles of the detector.

Scanning electrochemical microscopy (SECM) studies of catalytic EC′ processes: theory and experiment for feedback, generation/collection and imaging measurements

This paper describes the use of scanning electrochemical microscopy (SECM) in the tip generation/substrate collection (TG/SC), or feedback, mode and substrate generation/tip collection (SG/TC) mode to measure homogeneous kinetics in the catalytic EC' process. Theoretical analyses of both configurations have been developed numerically to allow the optimal conditions for sensitive kinetic measurements to be determined. This is shown to involve collection efficiency measurements as a function of tip-substrate electrode distance in the case of TG/SC measurements and tip (collector current) images in a plane normal to the substrate electrode for the SG/TC mode. An important consideration for the SECM configuration (particularly for TG/SC and feedback measurements) is that the electroinactive co-reactant may be depleted more significantly than with other electrode geometries, because of cycling of the redox couple in the tip/substrate electrode gap, while the co-reactant can only enter this gap by hindered diffusion. The approaches described are examined through studies of the oxidation of amidopyrine by electrogenerated Fe(CN) in 0.5 mol dm(-3) aqueous KOH solution. A second-order rate constant of 390 ± 80 dm(3) mol(-1) s(-1) is obtained from TG/SC measurements, consistent with SG/TC quantitative imaging measurements. The consistency of the kinetic measurements confirms the validity of the approaches described. The kinetic constant is lower than expected based on previous ultramicroelectrode (UME) studies, and this is attributed to the fact that background currents for the direct heterogeneous oxidation of amidopyrine are more significant with conventional UME measurements, which will tend to enhance the current measured and may therefore lead to an overestimation of kinetic constants. The TG/SC approach, on the other hand, provides a means of making dual-electrode collection efficiency measurements with diffusional feedback of the redox couple, leading to superior voltammetric responses and enabling more accurate kinetic determination.

Modeling Turbulent Multiphase Flow in Design of Nut Harvesters with Reduced Dust Emission and Low Power Demand

Computational fluid dynamics (CFD) modeling was evaluated for a physical prototype nut harvester as a method to determine model effectiveness for predicting dust emissions and reduced power demand in terms of pressure drop. Particle-laden gas was dilute and highly turbulent with an estimated particle volume fraction of 0.24% and gas flow Reynolds number of >105. Airflow simulations were based on the realizable k-e and Reynolds stress models; the stochastic Lagrangian discrete phase model determined particle collection and tracking characteristics. The predicted results of the gas flows from CFD simulations followed the trends of experimental data. CFD-guided design reduced airflow pressure drop by 43% to 54%, resulting in a corresponding reduction in power demand based on pressure drop measurements and simulations. Particle collection efficiencies for particle diameters of 10 m were increased by 3.6 to 5.4 times. The particle flow model was partially validated, although additional measurements of the particle collection efficiencies and particle locations may be required. The results indicated that nut harvester design modifications can be guided by CFD modeling.

Performance of thin pixel sensors irradiated up to a fluence of and development of a new interconnection technology for the upgrade of the ATLAS pixel system

Abstract A new pixel module concept is presented, where thin sensors and a novel vertical integration technique are combined. This R&D activity is carried out in view of the ATLAS pixel detector upgrades. A first set of n-in-p pixel sensors with active thicknesses of 75 and 150 μ m has been produced using a thinning technique developed at the Max-Planck-Institut Halbleiterlabor (HLL). Charge Collection Efficiency measurements have been performed, yielding a higher CCE than expected from the present radiation damage models. The interconnection of thin n-in-p pixels to the FE-I3 ATLAS electronics is under way, exploiting the Solid Liquid Interdiffusion (SLID) technique developed by the Fraunhofer Institut EMFT. In addition, preliminary studies aimed at Inter-Chip-Vias (ICV) etching into the FE-I3 electronics are reported. ICVs will be used to route the signals vertically through the read-out chip, to newly created pads on the backside. This should serve as a proof of principle for future four-side tileable pixel assemblies, avoiding the cantilever presently needed in the chip for the wire bonding.

A module concept for the upgrades of the ATLAS pixel system using the novel SLID-ICV vertical integration technology

The presented R&D activity is focused on the development of a new pixel module concept for the foreseen upgrades of the ATLAS detector towards the Super LHC employing thin n-in-p silicon sensors together with a novel vertical integration technology. A first set of pixel sensors with active thicknesses of 75 μm and 150 μm has been produced using a thinning technique developed at the Max-Planck-Institut für Physik (MPP) and the MPI Semiconductor Laboratory (HLL). Charge Collection Efficiency (CCE) measurements of these sensors irradiated with 26 MeV protons up to a particle fluence of 1016neqcm−2 have been performed, yielding higher values than expected from the present radiation damage models. The novel integration technology, developed by the Fraunhofer Institut EMFT, consists of the Solid-Liquid InterDiffusion (SLID) interconnection, being an alternative to the standard solder bump-bonding, and Inter-Chip Vias (ICVs) for routing signals vertically through electronics. This allows for extracting the digitized signals from the back side of the readout chips, avoiding wire-bonding cantilevers at the edge of the devices and thus increases the active area fraction. First interconnections have been performed with wafers containing daisy chains to investigate the efficiency of SLID at wafer-to-wafer and chip-to-wafer level. In a second interconnection process the present ATLAS FE-I3 readout chips were connected to dummy sensor wafers at chip-to-wafer level. Preparations of ICV within the ATLAS readout chips for back side contacting and the future steps towards a full demonstrator module will be presented.

Electron Recombination Kinetics and the Analysis of Collection Efficiency and Diffusion Length Measurements in Dye Sensitized Solar Cells

A significant difference exists between two measured estimates of the electron diffusion length in dye sensitized solar cells. One method is based on spectral response at short circuit (L1) and the other on small perturbations (Ln). Following a recent theoretical treatment of the diffusion length for “non first order recombination”, one can propose an “effective diffusion length” at short circuit (λn̅). Using simulation and measured values we show that L1 ≈ λn̅, for a wide range of recombination orders, despite the first order assumption made when deriving L1. We also show Ln ≈ λn̅, when Ln is derived from a time dependent full cell model incorporating non first order recombination. Thus the deviation of experimentally measured Ln from simulated Ln and L1 cannot be explained simply by the incorporation of nonlinear recombination. Our results give support to the spectral response method, but do not give a theoretical basis for rejecting the small perturbation method.

Multiscale three-dimensional simulations of charge gain and transport in diamond

A promising new concept of a diamond-amplified photocathode for generation of high-current, high-brightness, and low thermal emittance electron beams was recently proposed and is currently under active development. Detailed understanding of physical processes with multiple energy and time scales is required to design reliable and efficient diamond-amplifier cathodes. We have implemented models, within the VORPAL computational framework, to simulate secondary electron generation and charge transport in diamond in order to facilitate the investigation of the relevant effects involved. The models include inelastic scattering of electrons and holes for generation of electron-hole pairs, elastic, phonon, and charge impurity scattering. We describe the integrated modeling capabilities we developed and present results on charge gain and collection efficiency as a function of primary electron energy and applied electric field. We compare simulation results with available experimental data. The simulations show an overall qualitative agreement with the observed charge gain from transmission mode experiments and have enabled better understanding of the collection efficiency measurements.

Properties of a radiation-induced charge multiplication region in epitaxial silicon diodes

Charge multiplication (CM) in p+n epitaxial silicon pad diodes of 75, 100 and 150μm thickness at high voltages after proton irradiation with 1MeV neutron equivalent fluences in the order of 1016cm−2 was studied as an option to overcome the strong trapping of charge carriers in the innermost tracking region of future Super-LHC detectors. Charge collection efficiency (CCE) measurements using the Transient Current Technique (TCT) with radiation of different penetration (670, 830, 1060nm laser light and α-particles with optional absorbers) were used to locate the CM region close to the p+-implantation. The dependence of CM on material, thickness of the epitaxial layer, annealing and temperature was studied. The collected charge in the CM regime was found to be proportional to the deposited charge, uniform over the diode area and stable over a period of several days. Randomly occurring micro-discharges at high voltages turned out to be the largest challenge for operation of the diodes in the CM regime. Although at high voltages an increase of the TCT baseline noise was observed, the signal-to-noise ratio was found to improve due to CM for laser light. Possible effects on the charge spectra measured with laser light due to statistical fluctuations in the CM process were not observed. In contrast, the relative width of the spectra increased in the case of α-particles, probably due to varying charge deposited in the CM region.

A Comprehensive Technique for Determining the Intrinsic Light Yield of Scintillators

Precise knowledge of the intrinsic light yield of scintillating materials is important for characterizing, optimizing, and simulating scintillating detectors for radiation detection applications. We present here a comprehensive method for determining the intrinsic light yield of scintillating materials. By maintaining complete control over all aspects of photodetector response measurement, and through the use of a novel method for direct measurement of the light collection efficiency of the scintillator, we have successfully demonstrated that our technique allows for new levels of precision and understanding in the measurement of the intrinsic light yield of scintillating materials.

Performance of a Novel Rotating Gas-Liquid Separator

A novel gas separation process makes use of a rotating phase separator to separate micron-sized droplets from a gas stream. Based on an industrial scale design, a water/air separator is constructed and tested. The first experiment concerns the drainage of large fractions of separated liquid. During operation, drainage is observed via windows and a descriptive model is formulated. Because of the major influence on overall separation efficiency, liquid drainage is a key issue in the separator design. The second experiment comprises a droplet collection efficiency measurement using micron-sized droplets dispersed within the airstream. The separation efficiency of fine droplet removal is measured. This is an important factor in reducing capital costs.

Comparison of pad detectors produced on different silicon materials after irradiation with neutrons, protons and pions

A set of 44 pad detectors produced on p- and n-type MCz and Fz wafers was irradiated with 23 GeV protons, 200 MeV pions and reactor neutrons up to the equivalent fluences of Φ eq = 3 × 10 15 cm - 2 . The evolution of the full depletion voltage and the leakage current were monitored during short- and long-term annealing. At selected representative annealing steps, charge collection measurements were performed for all samples with LHC speed electronics. Measurements of full depletion voltage, leakage current and charge collection efficiency were compared for different irradiation particles and silicon materials.

Characterization of irradiated P-type silicon detectors by the ALIBAVA system

The ATLAS Tracker System has been designed to withstand the radiation doses accumulated with 10 years of running at a LHC luminosity of 10 34 cm - 2 s - 1 . The operation under an upgraded luminosity of 10 35 cm - 2 s - 1 (superluminous LHC) implies to upgrade the semiconductor tracking systems of the LHC experiments. The expected dose for the inner detector trackers at the superluminous LHC experiments is up to 10 16 1 MeV equivalent neutron cm - 2 after the envisaged five years of operation. Investigations have showed arguments in favour of implementing the n-type strip readout on a p-type substrate (currently the Semiconductor Tracker, SCT, uses p-type strip readout on a n-type substrate). In order to evaluate the radiation damage p-type microstrip sensors have been irradiated with neutrons and protons at several fluxes up to 10 16 cm - 2 . Electrical and charge collection efficiency measurements have been carried out by means of a radioactive source setup as well as by an infrared laser illumination and the measurements compared with a non-irradiated sensor as a reference. The ALIBAVA acquisition system has been used. It is a compact and portable system which contains two front-end readout chips (Beetle chip) to acquire the detector signals. One of the advantages of the ALIBAVA system is that it uses LHC speed electronics. Another one is that it performs a pulse by pulse and strip by strip analysis.

Study on [formula omitted] thick n- and p-type epitaxial silicon sensors irradiated with 24 GeV/ c protons and 1 MeV neutrons

A study on 150 μ m epitaxial (EPI) n- and p-type silicon diodes irradiated with neutrons up to 8 × 10 15 n / cm 2 and protons up to 1.7 × 10 15 p / cm 2 has been performed by means of CV/IV, charge collection efficiency (CCE) and transient current technique (TCT) measurements. It is found that the effective space charge density increases three times faster after proton than after neutron irradiation with a slightly higher effective space charge generation rate for n-type material compared to p-type material. A drop in charge collection efficiency already at fluences of 1 × 10 12 n eq / cm 2 can be seen in n-type material, but is absent in p-type material. TCT measurements show space charge sign inversion from positive to negative charge in n-type material after neutron irradiation and from negative to positive space charge in p-type material after proton irradiation. No difference was found in the response of diodes manufactured by different producers out of the same wafer material.

Charge collection efficiencies of planar silicon detectors after reactor neutron and proton doses up to [formula omitted

The planned luminosity upgrade of the large hadron collider at CERN (Super-LHC) will provide a challenging environment for the tracking and vertexing detector systems. The innermost devices at a radius about 4 cm from the interaction region will have to be able to withstand a combined charged and neutron hadron dose in the order of 10 16 1 MeV neutron equivalent particles ( n eq ) per square centimeter over the anticipated 5 year lifespan of the SLHC experiments. Planar, segmented silicon detectors with n-strip readout are one of the many radiation tolerant technologies under consideration for use for the Super-LHC tracking detectors in either pixel or strip geometries. This paper details charge collection efficiency measurements made with silicon sensors that have been irradiated to doses as high as 1.5 × 10 16 n eq cm - 2 with reactor neutrons and as high as 1.6 × 10 16 n eq cm - 2 with 26 MeV protons and 24 GeV protons. In this study, n + segmented strip readout in either n-bulk (n-in-n) or p-bulk (n-in-p) substrates are considered. Both diode configurations were processed in substrates grown with float zone (FZ) and magnetic Czochralski (MCz) techniques. For the fluences studied, all the n + strip readout technologies are still viable assuming that adequate bias voltage and cooling can be supplied and low noise, low threshold readout electronics can be designed.

Modeling and Analysis of Charged-Particle CMOS Image Sensor Arrays

Direct-detection CMOS image sensors optimized for charged-particle imaging applications, such as electron microscopy and particle physics, have been designed, fabricated and characterized. Based on standard silicon CMOS active pixel sensor (APS) technology, the sensor arrays uses an 8 to 20 mum epitaxial layer that acts as a thicker sensitive region in the generation and collection of ionization electrons resulting from impinging high-energy particles. A range of optimizations to this technology have been developed via simulation and experimental device design. These include the simulation and measurement of charge collection efficiency versus recombination, effect of diode size and stray capacitance versus signal gain and noise, and the effect of different epitaxial silicon depths and the energy of incident electrons. Results from several experimental devices are presented and compared with simulations, including measurements from two prototypes that systematically and independently vary pixel pitch and diode area.

Charge Collection Efficiency Measurements of Heavily Irradiated Segmented n-in-p and p-in-n Silicon Detectors for Use at the Super-LHC

The planned luminosity upgrade of the Large Hadron Collider at CERN (Super-LHC) will provide a challenging environment for the tracking and vertexing detector systems. With a proposed nearly 10-fold luminosity increase to 1035 cm2 middot s-1, the innermost devices will have to be able to withstand a hadron dose on the order of 1times1016 1 MeV neutron equivalent per square centimeter over the anticipated five year lifetime of the experiments. Planar, segmented silicon detectors with n-strip readout are one of the radiation tolerant technologies under consideration for use for the Super-LHC tracking detectors in either pixel or strip geometries. This paper details measurements made with n-strip (n-in-p) and p-strip (p-in-n) planar devices that have been irradiated to doses as high as 1times1016 neq cm-2 with reactor neutrons and fast protons. The doses under study cover the expected range of final fluences for the different tracking systems of the ATLAS and CMS experiments at the Super-LHC. The charge collection measurements have been carried out using analogue, high-speed (40 MHz) electronics and a Strontium electron source. These measurements show that p-in-n sensors are not radiation tolerant enough for the requirements of the micro-strip detectors at the SLHC; whereas, the charge collection properties exhibited by the n-in-p strip devices may be sufficient for all tracker regions (pixels and strips) of the SLHC assuming that appropriate low noise and threshold readout electronics are designed and adequate bias voltage can be routed to the sensors.

Electrohydrodynamic flow and particle collection efficiency of a spike-plate type electrostatic precipitator

In this work, the results of electrohydrodynamic (EHD) secondary flow and particle collection efficiency measurements in a spike-plate type electrostatic precipitator (ESP) are presented. The EHD secondary flow was measured using 2- and 3-dimensional particle image velocimetry (PIV) method under the negative DC voltage. The PIV measurements were carried out in several cross-sectional planes along and across the ESP duct. The results show a complex and turbulent flow structure in the ESP. The EHD secondary flow significantly depends on applied voltage and measuring cross-sectional plane position in respect to the spike tip. The partial collection efficiency of the ESP was measured for negative and positive DC voltage. The particle concentration with and without discharge was measured at the ESP exit using an optical aerosol spectrometer.