High-energy Lines Research Articles

Physics design of an accelerator for an accelerator-driven subcritical system

An accelerator-driven subcritical system (ADS) program was launched in China in 2011, which aims to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power in multiple phases lasting about 20 years. The driver linac is defined to be 1.5 GeV in energy, 10 mA in current and in cw operation mode. To meet the extremely high reliability and availability, the linac is designed with much installed margin and fault tolerance, including hot-spare injectors and local compensation method for key element failures. The accelerator complex consists of two parallel 10-MeV injectors, a joint medium-energy beam transport line, a main linac, and a high-energy beam transport line. The superconducting acceleration structures are employed except for the radio frequency quadrupole accelerators (RFQs) which are at room temperature. The general design considerations and the beam dynamics design of the driver linac complex are presented here.

Fermi energy shift in deposited metallic nanotubes: A Raman scattering study

The longitudinal optical phonon of metallic nanotubes shifts by 23 cm${}^{\ensuremath{-}1}$ to lower energies when the nanotubes are deposited from a solution onto a substrate. The linewidth increases by 13 cm${}^{\ensuremath{-}1}$. The changes are explained in terms of shifts in the Fermi energy that influence the Kohn anomaly in the longitudinal optical phonon branch in metallic nanotubes. Using in situ electrochemical Raman measurements we show that the Fermi energy is 0.16 eV below its intrinsic value in metallic nanotubes in solution. Our results impact the application of Raman spectroscopy to distinguish between metallic and semiconducting tubes by examining the high-energy mode line shape.

Characterization of superconducting wires and cables by X-ray micro-tomography

Due to their mechanical strength and ability to withstand the large electromagnetic force applied to the superconductors in large magnets during excitation, the Cable-in-Conduit-Conductor (CICC) type superconductors will be employed in the next stage of fusion magnets. Here, we discuss the recent results on the application of a non-invasive method for the characterization of CCIC by X-ray micro-tomography (μXCT). The experiments have been carried out on a high resolution X-ray tomograph in INFLPR (http://tomography.inflpr.ro). An open type nanofocus X-ray source with maximum high voltage of 225kVp at 15–30W maximum power and multiple targets of W on different windows materials (Be, Al, Cu or diamond) is the main component. X-rays are detected by means of amorphous silicon flat panel sensor in the cone-beam configuration and high-energy efficient line sensor based on individual scintillators in the fan-beam scanning configuration. The quality of tomographic images (≈40μm space resolution) allowed the majority of strands of analyzed CICC samples to be fully reconstructed along the investigated segment (up to 300mm long). Our method provides: (i) local and global void fractions (over a 300mm length of the sample), (ii) void homogeneity factor as the ratio between void space surface and perimeter and (iii) twist pitch angle of individual strands and its distribution in 3D. It can be used to investigate superconducting CICC during their manufacture, installation or after service inspection, for purposes of QA, characterization or development.

Intrinsic normalized emittance growth in laser-driven electron accelerators

Laser-based electron sources are attracting strong interest from the conventional accelerator community due to their unique characteristics in terms of high initial energy, low emittance, and significant beam current. Extremely strong electric fields (up to hundreds of $\mathrm{GV}/\mathrm{m}$) generated in the plasma allow accelerating gradients much higher than in conventional accelerators and set the basis for achieving very high final energies in a compact space. Generating laser-driven high-energy electron beam lines therefore represents an attractive challenge for novel particle accelerators. In this paper we show that laser-driven electrons generated by the nowadays consolidated TW laser systems, when leaving the interaction region, are subject to a very strong, normalized emittance worsening which makes them quickly unusable for any beam transport. Furthermore, due to their intrinsic beam characteristics, controlling and capturing the full beam current can only be achieved improving the source parameters.

Gamma-ray spectrometric measurements of fission rate ratios between fresh and burnt fuel following irradiation in a zero-power reactor

The gamma-ray activity from short-lived fission products has been measured in fresh and burnt UO2 fuel samples after irradiation in a zero-power reactor. For the first time, short-lived gamma-ray activity from fresh and burnt fuel has been compared and fresh-to-burnt fuel fission rate ratios have been derived.For the measurements, well characterized fresh and burnt fuel samples, with burn-ups up to 46GWd/t, were irradiated in the zero-power research reactor PROTEUS. Fission rate ratios were derived based on the counting of high-energy gamma-rays above 2200keV, in order to discriminate against the high intrinsic activity of the burnt fuel.This paper presents the measured fresh-to-burnt fuel fission rate ratios based on the 142La (2542keV), 89Rb (2570keV), 138Cs (2640keV) and 95Y (3576keV) high-energy gamma-ray lines. Comparisons are made with the results of Monte Carlo modeling of the experimental configuration, carried out using the MCNPX code. The measured fission rate ratios have 1σ uncertainties of 1.7–3.4%. The comparisons with calculated predictions show an agreement within 1–3σ, although there appears to be a slight bias (∼3%).

A Project for synchrotron with electron cooling for cancer therapy

A project for a new generation of proton and ion accelerator facilities for cancer therapy has been developed at the Budker Institute of Nuclear Physics (BINP), Siberian Branch, Russian Academy of Sciences (SB RAS). This facility includes an electrostatic injector, a booster with a 10-Hz repetition rate, and a main synchrotron with electron cooling and beam transport lines for delivering the beam to treatment rooms. The application of electron cooling makes it possible to increase the beam intensity and reduce the apertures of both the synchrotron and the high-energy transport lines, as well as save construction costs and energy consumption as required by the accelerator complex. This paper describes the main features of the synchrotron and the requirements for its main systems and their parameters.

Experimental and numerical evaluation of debris transport augmentation by turbulence during the recirculation-cooling phase of a LOCA

In resolving the safety issue of sump clogging due to debris generated by the type of high-energy line break known as a GSI-191 event, determination of the debris transport fraction, which is likely to be augmented by fluid turbulence during the recirculation cooling phase of a pressurized water reactor (PWR), is very important in the sizing of the sump screen area. In the present study, the debris transport fraction during the recirculation cooling phase of the OPR1000 plant is evaluated with and without consideration of turbulence debris augmentation. To do this, first a computational fluid dynamics (CFD) analysis of the flooded containment floor during the recirculation cooling phase is performed to obtain mean flow fields and the turbulence kinetic energy field assuming a double-ended guillotine break of a hot leg. Then, experiments involving tumbling velocities measurements of the surrogate debris for the OPR1000 plant and supplementary CFD analyses are performed to verify the turbulence effect on debris transport. From these findings, the turbulence effect on the degree of debris floor tumbling augmentation was found to be represented by the algebraic sum of the mean horizontal velocity and the horizontal fluctuating velocity deduced from the turbulent kinetic energy (TKE). Based on this experimental finding and on the CFD analysis of the containment floor when flooded, the debris transport fraction is evaluated for typical fibrous types of debris, such as NUKON, with respect to two size classes. The result shows a considerable increase in the debris transport fraction when a turbulence effect is implemented compared to when it is not. Increases of 5.55 and 2.06 times are observed for large NUKON and small/fine NUKON, respectively. This result implies that the turbulence effect should be considered in the debris transport quantification for conservatism. It was also found that the debris transport fraction may change depending on which sump is active between the two sumps. For example, small/fine NUKON is much more transportable when a sump near the break operates compared to when a sump far from the break operates. This fact also implies that the location of the active sump should be considered as an important parameter in comprehensive debris transport evaluations given a maximum head loss at the sump screen.

Analytical Prediction of Ion Stripping Extraction From Isochronous Cyclotrons

Accelerated ion beams are often extracted from a cyclotron by stripping some of ion's electrons at the end of the acceleration process. Stripping extraction system is commonly designed and optimized using computer simulations of beam dynamics at a later stage of a cyclotron project. However, minor changes in the distance between the magnet poles are proven to cause large displacements of the optimal position of high-energy transport line. It is shown that simple analytical formulas give good prediction of the position and direction of beam exit after stripping extraction and are useful tool for preliminary facility layout planning.

원전 격실에 대한 최적 침수분석 방법

본 논문은 원자력발전소의 대형탱크 또는 배관파단에 따른 격실의 침수분석을 수행함에 있어 최적평가방법을 개발하여 원전에 실제로 적용하는 방법에 관한 논문을 작성하는데 목적이 있다. 주급수관파단사고 분석을 위해 RETRAN 전산코드를 사용하였다. 유출수 질량유량을 계산하는데 있어서 주급수제어밸브가 계통설계에 의거 원자로정지 후 5.0초 만에 닫히는 것으로 모델링하여 분석하였다. 출력 70% 운전시 방출유량이 가장 높은 것으로 나타났다. 방출 질량유량을 가지고 침수위를 계산한 결과 주급수관 격실의 최대 침수위는 1.43m로서 이는 안전성기기가 설치된 위치보다 낮아 원전의 안전정지에 미치는 영향이 없는 것으로 나타났다. In this paper a realistic bounding method for flooding analysis following rupture of large size of thanks and piping is defined. Mass and energy release during main feedwater line break accident is analyzed with RETRAN code. It is modeled that the main feed water control valve is closed in 5.0 seconds after reactor trip. In result of the analysis, largest mass and energy is discharged at 70% reactor power. The flood sources for main feedwater room are calculated when piping failure occurs in the high energy line and medium energy line. Based on the result of flood level (1.43m), it is investigated that all of the safety-related environmental qualification equipments are well located above the flood level.

New external beam and particle detection set-up of Liège cyclotron – First applications of high energy beams to cultural heritage

Improvements on the Liége cyclotron have yielded an energy resolution comparable to that of classic electrostatic accelerators. The latest upgrades of the High-Energy High-Resolution beam line (HE-HR) are presented which consist of the addition of both a new extraction nozzle for non-invasive in-air measurements and a new particle-detection setup developed to take full advantage of the increased probed thickness with depth sensitive analytical methods. The suitability of the new setup and the advantages provided by the larger flexibility in choosing both the proper particle with an extended energy available will be illustrated by discussing latest results of studies recently led on Roman gilding techniques on cultural heritage artifacts by means of “High-Energy” alpha backscattering spectrometry combined with PIXE.

Optical measurements of single CdTe self-assembled quantum dots grown on ZnTe/GaSb

The CdTe quantum dots (QDs) grown on a ZnTe epilayer deposited directly on a GaSb substrate are studied by transmission electron microscopy (TEM) and near-field scanning optical microscopy. High resolution TEM images show CdTe QD of planoconvex shape. Near-field photoluminescence (NPL) in an applied magnetic field is used to measure the Zeeman splitting and diamagnetic shift of single CdTe QDs. Finally, time resolved NPL measurements suggest that the higher energy lines in the CdTe QD NPL spectra correspond to exciton transitions occurring in larger CdTe QDs and have shorter exciton lifetimes.

ICONE19-43390 INVESTIGATIONS ON PRESSURE DROP CHARACTERISTICS AND DISPOSAL OPTIMIZATION OF CONFLUX CHANNELS OF CONTAINMENT SUMP STRAINERS

In the event of LOCA (Loss-of-Coolant Accident) or HELB (High Energy Line Break) within the containment of a light-water reactor (LWR), some debris will be transported to and accumulate on the containment sump strainers by the steam/water flows induced by the break and by the containment sprays. And pressure loss will be introduced by the accumulated debris, which will decrease the available net positive suction head (NPSH) of circulating pumps of emergency core cooling system (ECCS) and containment spray system (CSS). Then cavitations may occur to induce the failure of ECCS and CSS pumps. Consequently it is necessary to carry out calculation and experiment to investigate the pressure drop characteristics of containment sump strainers. In the event of LOCA or HELB, the pressure drop of containment sump strainers is mainly composed of the pressure drop introduced by debris bed, strainer screen and the conflux channels. The authors established 3-D computational simulations to conduct investigations on the velocity field distribution and the pressure field distribution of water flow in the conflux channels. By analyzing pressure drop characteristics, the design optimization and disposal optimization were brought forward to minimize the pressure loss.

The methanol lines and hot core of OMC2-FIR4, an intermediate-mass protostar, withHerschel/HIFI

In contrast with numerous studies on the physical and chemical structure of low- and high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel SurveyS of star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10^-6 is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is consistent with abundances previously seen in low-mass hot cores. Furthermore, the highest energy lines at the highest frequencies display asymmetric profiles, which may arise from infall around the hot core.

Pulse compression below 40fs at 1μm: The first step towards a short-pulse, high-energy beam line at LULI

We present the upgrading project ELFIE (Equipement Laser de Forte Intensité et Energie) based on the "100TW" mixed Nd:glass CPA laser system at 1μm at LULI, which includes an energy enhancement and the development of a short-pulse, high-energy, good temporal contrast beam line (50fs/5J). We report the first experimental step towards the short-pulse, high-energy beam line: spectral broadening above 60nm from 7nm and temporal pulse compression below 40fs from 300fs at 1μm through a Krypton-filled hollow fiber compressor.

Annulus pressurization load evaluation after high energy line break

In Light Water Reactor design, it is required by the US Nuclear Regulatory Commission (NRC) that a conservative method must be used to estimate the loads on the Reactor Pressure Vessel (RPV) and components in the analysis of the loss of coolant accident (LOCA). As part of the safety design of the containment for light water reactors, jet forces resulting from the postulated rupture of high-pressure piping are accounted for in the design of internal structures. Traditionally, the jet force was estimated using ANS 58.2. However, it does not address the compressibility, reflection, and feedback amplification of the pressure forces as directed by NRC. In this paper, a numerical method is developed to estimate the annulus pressurization caused by the high-energy line break in the Economic Simplified Boiling Reactor (ESBWR). The pressure loading time history caused by the blast wave was predicted by the method. From the prediction, the maximum pressure loading was obtained. The method and the results have been submitted to the NRC as the supporting documents for the ESBWR certification.

Transmission of Shielding Materials for Particle Therapy Facilities

A typical particle therapy facility consists of an injector, a cyclotron or a synchrotron, a high-energy transport beam line, several treatment rooms including fixed-beam and gantry rooms, and even a research area. During the operation of these facilities, radiation is produced with neutrons being the dominant component outside the shielding. These facilities have large amounts of shielding with concrete thicknesses ranging up to ~5 m or more. Space required for shielding can be minimized by using composite shielding or high-density material such as Ledite® (manufactured by Atomic International, Frederick, Pennsylvania). Transmission data for radiation from protons and carbon ions incident on tissue targets with energies in the therapeutic energy range of interest were derived using the Monte Carlo code FLUKA for three different compositions of Ledite. Use of Ledite® or composite shielding results in space savings when compared to concrete.

THE PHOTOIONIZED ACCRETION DISK IN HER X-1

We present an analysis of several high-resolution Chandra grating observations of the X-ray binary pulsar Her X-1. With a total exposure of 170 ks, the observations are separated by years and cover three combinations of orbital and super-orbital phases. Our goal is to determine distinct properties of the photoionized emission and its dependence on phase-dependent variations of the continuum. We find that the continua can be described by a partial covering model which above 2 keV is consistent with recent results from \rxte studies and at low energies is consistent with recent \xmm and \sax studies. Besides a powerlaw with fixed index, an additional thermal blackbody of 114 eV is required to fit wavelengths above 12 \AA ($\sim$ 1 keV). We find that likely all the variability is caused by highly variable absorption columns in the range (1 -- 3)$\times 10^{23}$ cm$^{-2}$. Strong Fe K line fluorescence in almost all observations reveals that dense, cool material is present not only in the outer regions of the disk but interspersed throughout the disk. Most spectra show strong line emission stemming from a photoionized accretion disk corona. We model the line emission with generic thermal plasma models as well as with the photoionization code XSTAR and investigate changes of the ionization balance with orbital and superorbital phases. Most accretion disk coronal properties such as disk radii, temperatures, and plasma densities are consistent with previous findings for the low state. We find that these properties change negligibly with respect to orbital and super-orbital phases. A couple of the higher energy lines exhibit emissivities that are significantly in excess of expectations from a static accretion disk corona.

Optical polarization anisotropy of a-plane GaN/AlGaN multiple quantum well structures grown on r-plane sapphire substrates

A series of nonpolar a-plane GaN/AlGaN multiple quantum well structures of varying quantum well width have been studied by polarization resolved photoluminescence and photoluminescence excitation spectroscopy at low temperature. The photoluminescence spectra from all the structures show two features that are observed to blueshift with reducing well width. The lower energy feature is associated with the recombination of carriers in regions of the wells intersected by basal-plane stacking faults, while the higher energy line is attributed to localized exciton recombination involving only the quantum wells. Using excitation spectroscopy with polarized light, we were able to resolve exciton features associated with both the |Y⟩ and |Z⟩ valence sub-bands. The observed polarization dependence of the transitions is consistent with a modification to the valence band-edge states due to anisotropic biaxial compressive strain in the quantum well. We were also able to determine the exciton binding energies directly from the photoluminescence excitation spectra, which were found to increase from 36 to 76 meV as the quantum well width reduced from 60 to 35 Å.

Constraints on the kinematics of the ${^{44}}$Ti ejecta of Cassiopeia A from INTEGRAL/SPI

The medium-lived 44Ti isotope is synthesised by explosive Si-burning in core-collapse supernovae. It is extremely sensitive to the dynamics of the explosion and therefore can be used to indirectly probe the explosion scenario. The young supernova remnant Cassiopeia A is to date the only source of gamma-ray lines from 44Ti decay. The emission flux has been measured by CGRO/COMPTEL, BeppoSAX/PDS and INTEGRAL/IBIS. The high-resolution spectrometer SPI on-board the INTEGRAL satellite can provide spectrometric information about the emission. The line profiles reflect the kinematics of the 44Ti in Cassiopeia A and can thus place constraints on its nucleosynthesis and potentially on the associated explosion process. Using 4 years of data from INTEGRAL/SPI, we have searched for the gamma-ray signatures from the decay of the 44Ti isotope. The overwhelming instrumental background noise required an accurate modelling and a solid assessment of the systematic errors in the analysis. Due to the strong variability of the instrumental background noise, it has not been possible to extract the two lines at 67.9 and 78.4keV. Regarding the high-energy line at 1157.0keV, no significant signal is seen in the 1140-1170keV band, thereby suggesting that the line signal from Cassiopeia A is broadened by the Doppler effect. From our spectrum, we derive a ~ 500km/s lower limit at 2sigma on the expansion velocity of the 44Ti ejecta. Our result does not allow us to constrain the location of 44Ti since the velocities involved throughout the remnant, derived from optical and X-ray studies, are all far above our lower limit.

Erratum: “An Extensive Collection of Stellar Wind X‐Ray Source Region Emission Line Parameters, Temperatures, Velocities, and Their Radial Distributions as Obtained fromChandraObservations of 17 OB Stars” (ApJ, 668, 456 [2007

Erratum: “An Extensive Collection of Stellar Wind X‐Ray Source Region Emission Line Parameters, Temperatures, Velocities, and Their Radial Distributions as Obtained from<i>Chandra</i>Observations of 17 OB Stars” (ApJ, 668, 456 [2007