Results 1 - 10 of 853
Results 1 - 10 of 853. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] The National High Magnetic Field Laboratory's Pulsed Field Facility at Los Alamos National Laboratory is one of few research centers in the world that can create and use ultrahigh pulsed magnetic field for scientific research. The facility houses several types of nondestructive pulsed magnets which can provide the peak fields ranging from 60 to 100 T for users. This study will report the status of the user magnets and recent magnet developments to improve the quality and magnetic fields of our user magnets. In particular, this paper will present a new cooling technique that significantly reduces the cooling time without affecting the mechanical performance of the magnets. A possible upgrade of our facility with a new duplex magnet that is powered by a 4-MJ capacitor bank to deliver 80 T for users will be also reported. Finally, in addition, we will discuss some valuable lessons learned from magnet failures at our facility and possible further magnet design improvements to increase the magnet longevity or peak magnetic fields.
[en] An outline of this presentation of what a Differential Die-Away (DDA) instrument can do are: (1) Principle of operation of DDA instrument; (2) Determination of initial enrichment (IE) (σ < 5%); (3) Determination of burn up (BU) (σ ∼ 6%); (4) Determination of cooling time (CT) (σ ∼ 20-50%); and (5) DDA instrument as a standalone device. DDA response (fresh fuel vs. spent fuel) is: (1) Fresh fuel => DDA response increases (die-away time is longer) with increasing fissile content; and (2) Spent fuel => DDA response decreases (die-away time is shorter) with higher burn-up (i.e. more neutron absorbers present).
[en] The Rayleigh–Taylor instability which is responsible for the occurrence of narrow upward jets is studied in the scope of the nonhydrostatic model with horizontally nonuniform density and the Newtonian cooling. As analysis shows, the total hierarchy of instabilities in this model consists of three regimes—collapse, algebraic instability, and inertial motion. Realization of these stages, mutual transitions, and interference depend on a ratio between two characteristic time scales—collapse time and cooling time.
[en] The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied. The results show that the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well as with the decrease in cooling rate. Iron addition alone is more effective than either Si or Fe+Si additions in producing intermetallics. The binary Al-Fe phases predominate at low cooling rates and a high Fe: Si ratio; the β-Al5FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-AI8Fe2Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al4FeSi2 intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt% and higher. Calculations of the solidification paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification paths The theoretical models of Brody and Flemings (24), and Clyne and Kurz (25) also fail to explain the departure from the Scheil behavior. An adjusted 500oC metastable isothermal section of the Al-Si-Fe phase diagram has been proposed (in place of the equilibrium one), that correctly predicts the intermetallic phases that occur in this part of the system at low cooling rates (∼0.2 oC/s). (author)
[en] The MARS15 code provides contact residual dose rates for relatively large accelerator and experimental components for predefined irradiation and cooling times. The dose rate at particular distances from the components, some of which can be rather small in size, is calculated in a post Monte-Carlo stage via special algorithms described elsewhere. The approach is further developed and described in this paper.
[en] Thermal Analysis (TA) is the measurement of changes in a physical property of a material that is heated through a phase transformation temperature range. The temperature changes in the material are recorded as a function of the heating or cooling time in such a manner that allows for the detection of phase transformations. In order to increase accuracy, characteristic points on the cooling curve have been identified using the first derivative curve plotted versus time. In this paper, an alternative approach to the analysis of the cooling curve has been proposed. The first derivative curve has been plotted versus temperature and all characteristic points have been identified with the same accuracy achieved using the traditional method. The new cooling curve analysis also enables the Dendrite Coherency Point (DCP) to be detected using only one thermocouple. (author)
[en] High-energy electron cooling of RHIC presents many unique features and challenges. An accurate estimate of the cooling times requires a detailed calculation of the cooling process, which takes place simultaneously with various diffusive mechanisms in RHIC. In addition, many unexplored effects of high-energy cooling in a collider complicate the task of getting very accurate estimates of cooling times. To address these high-energy cooling issues, a detailed study of cooling dynamics based on computer codes is underway at Brookhaven National Laboratory. In this paper, we present an update on code development and its application to the high-energy cooling dynamics studies for RHIC
[en] Pebble divertor concept is proposed for high-power density steady state fusion reactor. In this system, the dropping pebbles receive the divertor plasma and the pebbles are circulated to be cooled down. In this report, the total storage amount of pebble in the circulation system is estimated. That total amount depends on the pebble cooling time, which is the duration that the temperature of the pebbles after irradiation is recovered to the initial temperature before irradiation. The pebble cooling time is changed by how the pebbles are cooled. In this study, the pebbles are considered to be laid in the pebble cooling bed for the radiation sink and to be cooled at a concerned temperature. From the calculation, the desired pebble flow rate has been found to be 30 kg/s/m in toroidal direction at the slit width of 2.5 cm. The pebble cooling time becomes shorter when the pebble cooling bed is thinner or the initial temperature of pebbles before the irradiation is higher so that the storage amount of the pebble in the circulation system will be suppressed to small value
[en] Monte Carlo simulations were performed for the differential die-away (DDA) technique to quantify its capability to measure the fissile contents in spent fuel assemblies of 64 different cases in terms of initial enrichment, burnup, and cooling time. The DDA count rate varies according to the contents of fissile isotopes such as 235U, 239Pu, and 241Pu contained in the spent fuel assembly. The effective 239Pu concept was introduced to quantify the total fissile mass of spent fuel by weighting the relative signal contributions of 235U and 241Pu compared to that of 239Pu. The Monte Carlo simulation results show that the count rate of the DDA instrument for a spent fuel assembly of 4% initial enrichment, 45 GWD/MTU burnup, and 5 year cooling time is ∼ 9.8 x 104 counts per second (c/s) with the 100-Hz repeated interrogation pattern of 0 to 10 (micro)s interrogation, 0.2 ms to 1 ms counting time, and 1 x 109 n/s neutron source. The 244Cm neutron background count rate for this counting time scheme is ∼ 1 x 104 c/s, and thus the signal to background ratio is ∼10.
[en] This paper presents hot press forming of 22MnB5 steel blanks for high strength automotive components. The hot press forming was performed using Schenck press PEZ0673 machine with maximum press force of 1000 kN. Samples were square 22MnB5 blanks, of 50 × 60 mm dimension. A high temperature furnace was used to heat up the blanks to austenite temperature of 950°C. Samples were held at the austenite temperature prior to forming and quenching process. Three independent controlled parameters were cooling water temperature, press holding time and flow rate of water. Pressed samples were characterized for metallographic study, hardness properties and tensile properties. Metallographic study was conducted using Meiji optical microscope. Hardness was measured using Vickers indenter with load 1000gf. From metallographic study, the hot pressed 22MnB5 boron steel samples produced lath martensitic microstructure. Hardness of hot pressed samples increased with decreasing cooling time. The yield strength and the ultimate tensile strength of samples after hot forming were between 1546 and 1923 N/mm"2. These findings were important to design tailored ultra-high strength in automotive components at different process parameter settings