Sufficient Number Of Photons Research Articles

Performance assessment of spectroscopic measurements of hydrogen and beryllium influxes and ionization fronts in ITER divertor plasmas using the divertor impurity monitor

Characteristics of Hα and Be II emissions in ITER divertor plasmas have been evaluated, and the applicability of a spectroscopic evaluation method of influxes and ionization front positions by using the divertor impurity monitor (DIM) has been systematically verified for the first time based on plasma profile datasets with parameter scans. In addition, practical values of the ionization/photon factor (S/XB) for DIM to evaluate influxes have been determined. In attached divertor plasmas and the onset of plasma detachment, H influx integrated over the entire area of the divertor can be evaluated within ±30 % accuracy using Hα intensities measured by the DIM and S/XB value of 32, which is higher than the S/XB in most divertor plasmas in previous devices owing to high electron density. The ionization front position can also be evaluated to within a few mm by using peak channel position. However, when electron temperature further decreases from the detachment onset, the ionizing plasma component (caused by electron impact excitation) in the total Hα emission decreases and the spatial profiles of emission and ionization diverge, making spectroscopic evaluation difficult. In all conditions, Hα intensities could be measured with a more than sufficient number of photons at the required time resolution using the current DIM design. For Be influx integrated over the entire divertor area, it has been found that Be I is not suitable for the DIM since its intensity is similar to the background continuous spectra. Replacing Be I with Be II solves this problem. Even in detached divertor plasmas, it is possible to evaluate Be1+ ionization flux within ±30 % accuracy using Be II intensities and S/XB, the value of which depends on the DIM’s fields of view. However, the evaluated Be1+ ionization flux is lower than Be influx by more than 80 %, meaning that the evaluation of Be influx using Be II would be an underestimate. But, Be II can be measured with a more than sufficient number of photons.

Development of the high energy engineering X-ray (HEX) superconducting wiggler, magnetic measurement, installation, and commissioning.

The High energy Engineering X-ray (HEX) diffraction beamline at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Lab (BNL) is the first high-energy beamline capable of reaching 200keV for a monochromatic beam. With the 3 GeV electron beam energy for the NSLS-II ring, only the superconducting wiggler (SCW) producing greater than 4T peak field can cover these ranges with a sufficient number of photons. The 1.2 m-long HEX-SCW has a period length of 70mm and a field strength on-axis of 4.3T. It utilizes no liquid helium, and the vertical aperture size of the electron beam vacuum chamber is 8mm. Unlike regular undulators/wigglers, there is no standard configuration for the magnetic measurement system for superconducting insertion devices. The NSLS-II Insertion Devices group has developed, in collaboration with the vacuum group, a novel in-vacuum Hall mapper with a 1.75m in-vacuum linear motor and an in-vacuum flip coil system utilizing many commercial-off-the-shelf products. The measurements were conducted at the BNL, and the device was installed in the ring and commissioned. This paper provides a description of the SCW and its magnetic measurement systems, as well as a brief account of the installation and commissioning efforts.

Construction of Cryogen-Free 4.3T Superconducting Wiggler for NSLS-II Ring

With the 3 GeV electron beam energy for the National Synchro-tron Light Source II (NSLS-II) ring, only superconducting wig-glers (SCW) producing greater than 4T peak field can cover the photon energy range of 20keV and 200keV with sufficient num-ber of photons. The High energy Engineering X-ray (HEX) Dif-fraction beamline, which is primarily funded by the New York State Energy Research and Development Authority (NYSERDA) and NSLS-II, will be equipped with a 1.2m-long SCW with 70mm period length and 4.3T on-axis field. This SCW is free from the use of liquid Helium and is cooled only with cryo-coolers. The Electron Beam Chamber (EBC) with vertical aper-ture of 8mm is made from 316LN stainless steel and copper plat-ing is applied both entire upper surface and +- 12.5mm wide from the center in the inner surface. The expected heat load from the electron beam of the NSLS-II ring is estimated to be 10W/m. This paper describes the design principles and engineering chal-lenges for the device.

Novel methods for measuring the optical parameters of the water Cherenkov detector

In this paper, novel methods are presented to measure the optical properties of the cylindrical water Cherenkov detector with high-reflectivity and diffuse reflection dominated Tyvek material as the inner surface. The mean transmission distance of photons between each reflection in the cylindrical water Cherenkov detector (the mean step length), is constant when there is a sufficient number of photons with random directions in the tank. The time distribution of the photons collected by the photomultiplier tube (PMT) in the water Cherenkov detector is approximately exponential, and the decay factor of the time distribution is determined by the absorption length of photons in the water, the reflectivity of the inner Tyvek surface, the mean step length of photons reflected in the tank, and the ratio of reflective Tyvek area to the total inner surface area. By considering the principles of photon propagation in the water Cherenkov detector, we developed novel methods to measure the water absorption length, Tyvek reflectivity, and mean step length of photons in the tank. The water absorption length and Tyvek reflectivity can be measured simultaneously by changing the height of the water, while the step length and Tyvek reflectivity in air can be measured simultaneously by changing the area of Tyvek, and the mean step length of photons can also be measured even all other parameters unknown. The proposed novel methods are supported by the deduction of formulae and verified by GEANT4 simulations and the prototype experiment.

X-rays from the redshift 7.1 quasar ULAS J1120+0641

Abstract We present X-ray imaging and spectroscopy of the redshift z = 7.084 radio-quiet quasar ULAS J112001.48+064124.3 obtained with Chandra and XMM–Newton. The quasar is detected as a point source with both observatories. The Chandra observation provides a precise position, confirming the association of the X-ray source and the quasar, while a sufficient number of photons is detected in the XMM–Newton observation to yield a meaningful X-ray spectrum. In the XMM–Newton observation, the quasar has a 2–10 keV luminosity of 4.7 ± 0.9 × 1044 erg s−1 and a spectral slope $\alpha = 1.6^{+0.4}_{-0.3}$ (where fν ∝ ν−α). The quasar appears to have dimmed in the 15 months between the two observations, with a 2–10 keV luminosity of $1.8^{+1.0}_{-0.7}\times 10^{45}$ erg s−1 during the Chandra observation. We derive optical-to-X-ray spectral slopes αOX of 1.76 ± 0.07 and $1.54^{+0.09}_{-0.08}$ at the times of the XMM–Newton and Chandra observations, respectively, consistent with the range of αOX found in other quasars of comparable ultraviolet luminosity. The very soft X-ray spectrum suggests that the quasar is accreting above the Eddington rate, $L/L_{\rm Edd} = 5^{+15}_{-4}$, compared to $L/L_{\rm Edd} = 1.2^{+0.6}_{-0.5}$ derived from the rest-frame ultraviolet. Super-Eddington accretion would help to reduce the discrepancy between the age of the quasar implied by the small size of the ionized near-zone in which it sits (<107 yr) and the characteristic e-folding time (2.5 × 107 yr if L/LEdd = 2). Such super-Eddington accretion would also alleviate the challenging constraints on the seed black hole mass provided that the quasar has been rapidly accreting throughout its history. The remnant of an individual Population III star is a plausible progenitor if an average L/LEdd > 1.46 has been maintained over the quasar's lifetime.

A novel technique for single-shot energy-resolved 2D x-ray imaging of plasmas relevant for the inertial confinement fusion

A novel x-ray diagnostic of laser-fusion plasmas is described, allowing 2D monochromatic images of hot, dense plasmas to be obtained in any x-ray photon energy range, over a large domain, on a single-shot basis. The device (named energy-encoded pinhole camera) is based upon the use of an array of many pinholes coupled to a large area CCD camera operating in the single-photon mode. The available x-ray spectral domain is only limited by the quantum efficiency of scientific-grade x-ray CCD cameras, thus extending from a few keV up to a few tens of keV. Spectral 2D images of the emitting plasma can be obtained at any x-ray photon energy provided that a sufficient number of photons had been collected at the desired energy. Results from recent inertial confinement fusion related experiments will be reported in order to detail the new diagnostic.

Requisites to realize high conversion efficiency of solar cells utilizing carrier multiplication

We have calculated the limiting conversion efficiency of solar cells utilizing carrier multiplication (CM), using the detailed balance theory. The solar cells were assumed to comprise quantum dots (QDs) embedded in another material. It has been elucidated that three requisites must be fulfilled, so that a sufficient number of photons in the solar spectrum contribute to CM, resulting in significantly higher conversion efficiency than the values of conventional cells. These requisites are as follows: (1) the effective mass of electrons in the QDs should be much lighter than that of holes, so that the threshold photon energy above which CM can occur is close to the energy gap of the QDs. In this respect, InAs is a promising candidate for the QD material, but PbSe and Si are not. (2) The potential barrier height for electrons in the QDs, which determines the upper limit of the quantum yield of photon-to-carrier conversion ( γ limit), should be slightly larger than the energy gap of the QDs to achieve a γ limit value of 2, when the solar cells are used under the non-concentrated insolation. InAs QDs embedded in Al x Ga 1− x As y Sb 1− y is a possible candidate to fulfill these two criteria. A higher barrier does not contribute to generation of more carriers, but likely disturbs electron transport. In contrast, under the concentrated insolation, a potential barrier slightly higher than twice the energy gap to achieve a γ limit value of 3 leads to higher conversion efficiency. (3) The quantum yield of photon-to-carrier conversion as a function of photon energy should rise as steeply as possible at the threshold photon energy. The experimentally observed quantum yield with a sloping rise leads to little improvement in conversion efficiency due to CM, under the non-concentrated insolation. Although it could be improved under the concentrated insolation, the conversion efficiency cannot reach the limiting value for triple-junction solar cells.

χ^2 analysis for estimating the accuracy of optical properties derived from time resolved diffuse-reflectance

Weighted residuals and the reduced chi(2) (chi(R) (2)) value are investigated with regard to their relevance for assessing optical property estimates using the diffusion equation for time-resolved measurements in turbid media. It is shown and explained, for all photon counting experiments including lifetime estimation, why chi(R) (2) increases linearly with the number of photons when there is a model bias. Only when a sufficient number of photons has been acquired, chi(R) (2) is a pertinent value for assessing the accuracy of mu(a) and mu(s)' estimates. It was concluded that chi(R) (2) is of particular interest for cases of small interfiber separation, low-level scattering, strong absorption and incorrect measurement of instrument response function. It was also found that chi(R) (2) is less pertinent for judging mu(a) in case of air boundary effects.

Dual objective fluorescence microscopy for single molecule imaging applications.

Fluorescence microscopy is an invaluable tool for studying biological processes in cells. In the recent past there has been significant interest in imaging cellular processes at the single molecule level. Single molecule experiments remove ensemble averaging effects and provide information that is typically not accessible through bulk experiments. One of the major requirements in single molecule imaging applications is that a sufficient number of photons be detected from the single molecule. This is not only important for the visual identification of single molecules, but also plays a crucial role in the quantitative analysis of the acquired data. Here, we demonstrate the use of a dual objective imaging configuration for single molecule studies. The configuration uses two opposing objective lenses, where one of the objectives is in an inverted position and the other objective is in an upright position. The use of opposing objective lenses has been previously demonstrated in 4pi confocal microscopy and I5M to achieve high axial resolution when compared to confocal/widefield microscopes. Here we demonstrate that the dual objective imaging configuration provides higher photon collection efficiency when compared to a regular microscope for a given illumination condition. As a result, single molecules can be localized with better accuracy when imaged through opposing objective lenses than when imaged through a regular optical microscope. Analytical tools are introduced to estimate the 2D location of single molecules and to characterize the accuracy with which they can be determined.

New scintillation detector of backscattered electrons for the low voltage SEM

The new scintillation detector of backscattered electrons that is capable of working at primary beam energy as low as 0.5 keV is introduced. Low energy backscattered electrons are accelerated in order to generate a sufficient number of photons. Secondary electrons are deflected back by the energy filter so that the true compositional contrast of the specimen is obtained. The theoretical models of the detector function are described and first demonstration images are presented.

Nanometer-localized multiple single-molecule fluorescence microscopy.

Fitting the image of a single molecule to the point spread function of an optical system greatly improves the precision with which single molecules can be located. Centroid localization with nanometer precision has been achieved when a sufficient number of photons are collected. However, if multiple single molecules reside within a diffraction-limited spot, this localization approach does not work. This paper demonstrates nanometer-localized multiple single-molecule (NALMS) fluorescence microscopy by using both centroid localization and photobleaching of the single fluorophores. Short duplex DNA strands are used as nanoscale "rulers" to validate the NALMS microscopy approach. Nanometer accuracy is demonstrated for two to five single molecules within a diffraction-limited area. NALMS microscopy will greatly facilitate single-molecule study of biological systems because it covers the gap between fluorescence resonance energy transfer-based (<10 nm) and diffraction-limited microscopy (>100 nm) measurements of the distance between two fluorophores. Application of NALMS microscopy to DNA mapping with <10-nm (i.e., 30-base) resolution is demonstrated.

Development of a time‐resolved optical tomography system for neonatal brain imaging

This Ph.D. project involved the development and evaluation of a prototype medical optical tomography system. The time‐resolved 32‐channel instrument is presented, and various instrumental aspects and performance issues are discussed. It has been designed primarily as a continuous bedside monitor for obtaining functional images of premature infants' brains that are at an increased risk of injury due to dysfunction in cerebral oxygenation or haemodynamics. The fully automated device employs 32 source fibers that sequentially deliver near infrared pulsed laser radiation of picosecond duration to the tissue. Transit time measurements of very high temporal resolution (∼100 ps FWHM) and stability (∼5 ps/h drift, and jitter of similar magnitude) are made between these sources and 32 detector optodes also located on the skin surface. Photons transmitted diffusely through the tissue and collected by the optodes are transmitted to four ultra‐fast eight‐anode Microchannel Plate Photomultiplier Tube detectors. Thirty‐two fully simplex time‐correlated single photon counting channels simultaneously record histograms of the photon flight times at rates of up to about 300,000 counts per second per channel. These so‐called temporal point spread functions represent the raw data for the image reconstruction. Separate maps of the internal absorption and scattering properties can be reconstructed from purely temporal data without recourse to reference or baseline measurements. The effectiveness of this instrument has been demonstrated by successfully imaging various tissue‐equivalent phantoms and an adult forearm. A preliminary post‐mortem study suggested that a sufficient number of photons can be transmitted across the head of the neonate at safe exposure levels and durations to obtain an adequate signal.

X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?

We investigate the X-ray properties of the Parkes sample of Bat-spectrum radio sources using data from the ROSAT All-Sky Survey and archival pointed PSPC observations. In total, 163 of the 323 sources are detected. For the remaining 160 sources, 2 sigma upper limits to the X-ray flux are derived. We present power-law photon indices in the 0.1-2.4 keV energy band for 115 sources, which were determined either with a hardness ratio technique or from direct fits to pointed PSPC data if a sufficient number of photons were available. The average photon index is lGamma g = 1.95(-0.12)(+0.13) for flat-spectrum radio-loud quasars, lGamma g = 1.70(-0.24)(+0.23) for galaxies, and lGamma g = 2.40(-0.31)(+0.12) for BL Lac objects. The soft X-ray photon index is correlated with redshift and with radio spectral index in the sense that sources at high redshift and/or with flat (or inverted) radio spectra have flatter X-ray spectra on average. The results are in accord with orientation-dependent unification schemes for radio-loud active galactic nuclei. Webster et al. discovered many sources with unusually red optical continua among the quasars of this sample, and interpreted this result in terms of extinction by dust. Although the X-ray spectra in general do not show excess absorption, we find that low-redshift optically red quasars have significantly lower soft X-ray luminosities on average than objects with blue optical continua. The difference disappears for higher redshifts, as is expected for intrinsic absorption by cold gas associated with the dust. In addition, the scatter in log(f(x)/f(o)) is consistent with the observed optical extinction, contrary to previous claims based on optically or X-ray selected samples. Although alternative explanations for the red optical continua cannot be excluded with the present X-ray data, we note that the observed X-ray properties are consistent with the idea that dust plays an important role in some of the radio-loud quasars with red optical continua.