This paper presents an initial study that is intended to explore the development of a scalable fully-implicit stabilized unstructured finite element (FE) capability for low-Mach-number resistive MHD. The discussion considers the development of the stabilized FE formulation and the underlying fully-coupled preconditioned Newton-Krylov nonlinear iterative solver. To enable robust, scalable and efficient solution of the large-scale sparse linear systems generated by the Newton linearization, fully-coupled algebraic multilevel preconditioners are employed. Verification results demonstrate the expected order-of-acuracy for the stabilized FE discretization of a 2D vector potential form for the steady and transient solution of the resistive MHD system. In addition, this study puts forth a set of challenging prototype problems that include the solution of an MHD Faraday conduction pump, a hydromagnetic Rayleigh-Bernard linear stability calculation, and a magnetic island coalescence problem. Initial results that explore the scaling of the solution methods are presented on up to 4096 processors for problems with up to 64M unknowns on a CrayXT3/4. Additionally, a large-scale proof-of-capability calculation for 1 billion unknowns for the MHD Faraday pump problem on 24,000 cores is presented.

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We present studies of space-charge-induced beam profile broadening at high intensities in the Proton Storage Ring (PSR) at Los Alamos National Laboratory. Previous work has associated the observed broadening in the vertical direction with the coherent half integer resonance. Here, we study the effect of the space charge environment on this resonance; specifically, we investigate the strength of the resonance versus beam intensity, longitudinal bunching factor, transverse lattice tune, and two different beam injection scenarios. For each case, detailed particle-in-cell simulations are combined with experimental results to elucidate the behavior and sensitivity of the beam resonance response.

In current waste packaging design, Alloy 22 (Ni-22Cr-13Mo-3W-3Fe) has been chosen as the candidate materials to fabricate a 2 cm outer layer of the high-level nuclear waste containers, as part of proposed geological repository at Yucca Mountain, Nevada. During the repository period, the container materials will be subject to the corrosion due to its exposure to the multi-ionic aqueous environments. Although Alloy 22 has demonstrated excellent corrosion resistance, but accumulation of small yearly corrosion rate for 10,000 or more years can be significant enough. The goal of this research is to seek alternative techniques to obtain a reasonably confident corrosion rate determination, since the conventional weight loss technique requires many years to achieve a detectable weight loss in Alloy 22 samples. This paper will discuss the latest experiment results in using potentiostatic technique to determine passive dissolution rates.

The Rapid Cycling Medical Synchrotron (RCMS) accelerator is under conceptual design at BNL. We report the results of the beam dynamics studies in the current design RCMS ring lattice with simulation program ORBIT++. In this paper, the designed RCMS ring lattice, the important physical parameters and the simulation program employed in this study are overviewed. The major elements and the numerical parameters included in the simulations are listed and discussed. The evolution of longitudinal beam properties, such as bunch length, bunch height and particle distributions, under RF voltage ramping are studied. The simulation results of the 6D beam dynamics during acceleration including phase space and emittance evolution are presented. Finally, the space charge effects such as tune shift and emittance growth in the RCMS ring are investigated and discussed.

The Spallation Neutron Source (SNS) extraction kicker system brings the proton beam from the accumulator ring through a beam transfer line into the target area. The 14 kicker magnets are located in one straight section. The kicker magnets are energized by 14 Blumlein type Pulse Forming Networks (BPFN). The first article of the SNS extraction kicker BPFN was assembled and tested at this laboratory. This paper describes the kicker BPFN system arrangement and parameters. The first article BPFN design and its main components used are explained. High voltage BPFN test results and the load current waveform are illustrated in this paper. Temperature measurements of the kicker ferrite blocks at full power showed only small or no heating. This paper discusses the modifications to the BPFN design, such as a saturating inductor and 25 Q termination, to minimize the transverse coupling impedance.

We study the influence of space charge on the crossing of the second-order resonance and the associated space-charge limit in high-intensity rings. Two-dimensional simulation studies are compared and found to agree with the envelope models in the finding of an increased intensity limit due to the coherent frequency shift. We also discuss application of this effect to bunched beams and multi-turn injection painting, and the effect of high-order resonances and issues of the envelope instability.

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The Spallation Neutron Source (SNS) Accumulator ring extraction system includes 14 modules of ferrite kicker magnets with window-frame geometry. Among all ring components, the extraction kickers make the single largest contribution to the coupling impedance budget. A prototype was constructed and various design options impacting the transverse coupling impedance have been thoroughly studied. Bench as well as system measurements were performed to determine the benefits from an external circuit resistance, from using different ferrites material, and from adding a novel ferrite winding. The results presented in this paper confirm that a resistive termination in the external circuit yields a solution with sufficiently reduced transverse coupling impedance. In order to determine the total contribution of all modules, an equivalent circuit and a simple scaling law was derived from measurements of full and half size magnets.

The accumulator ring of the Spallation Neutron Source (SNS) is designed to accept high-intensity H{sup -} beam of 1 GeV kinetic energy from the injecting LINAC, and to accumulate, in a time interval of 1 msec, 2 x 10{sup 14} protons in a single bunch of 700 nsec. In order to optimize the effective straight-section spaces for beam-injection, extraction and collimation, we have minimized the width of the large aperture quadrupoles which are located in the same straight sections of the accumulator ring with the injection and extraction systems. By minimizing the width of the quadrupoles to {+-}40.4 cm, the beam-injection and extraction angles are lowered to 8.75{sup o} and 16.8{sup o} respectively. Further optimization of the narrow quadrupole, minimizes the strength of the dodecapole multipole component of the quadrupole, thus reducing the width of the 12pole structure resonance and allowing a larger tune space for stability of the circulating beam. In this paper we present results derived from magnetic field calculations of 2D and 3D modeling, and discuss the method of optimizing the size of the quadrupole and minimizing its dodecapole multipole component.

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Bitmap indices are efficient data structures for querying read-only data with low attribute cardinalities. To improve the efficiency of the bitmap indices on attributes with high cardinalities, we present a new strategy to evaluate queries using bitmap indices. This work is motivated by a number of scientific data analysis applications where most attributes have cardinalities in the millions. On these attributes, binning is a common strategy to reduce the size of the bitmap index. In this article we analyze how binning affects the number of pages accessed during query processing, and propose an optimal way of using the bitmap indices to reduce the number of pages accessed. Compared with two basic strategies the new algorithm reduces the query response time by up to a factor of two. On a set of 5-dimensional queries on real application data, the bitmap indices are on average 10 times faster than the projection index.

The SNS Ring off-line parallel simulation environment based on the Unified Accelerator Libraries (UAL) has been implemented and used for extensive full-scale beam dynamics studies arising in high-intensity rings. The paper describes the structure of this environment and its application to the development and analysis of the SNS accumulator ring beam loss model including a complex combination of several physical effects.

One of the primary tasks in the design of the Spallation Neutron Source (SNS) ring is to control collective effects including space charge, transverse and longitudinal instabilities, and electron cloud. Transverse painting is used to alleviate space charge force; longitudinal painting along with chromatic sextupoles are used to enhance Landau damping; injection kicker vacuum pipes are carefully shielded, and extraction kicker impedances are measured in detail and optimized; beam halo, beam loss and electron production are minimized; finally, damping systems at various frequencies are planned. This paper summarizes these design implementations.

In the past, passive Nuclear Materials Identification System (NMIS) measurements on plutonium metal shells at VNIIEF have shown the sensitivity of the acquired covariance functions to shell mass and thickness for a variety of shell thicknesses from 6 to 30 mm and masses varying from 1829 to 4468g. The technique acquires the time-dependent coincidence distribution between plastic scintillators detecting radiation from the Pu. The measurements showed the sensitivity of the acquired signature to the different spontaneous emission, attenuation, and multiplication properties of the shells. In this work, the MCNP-POLIMI neutron and photon transport code was used to simulate passive measurements on plutonium metal and oxide. The code is a modified version of MCNP, which attempts to calculate more correctly quantities that depend on the second moment of the neutron and gamma distributions, and attempts to model detector pulses as closely as possible. MCNP-POLIMI, together with a post-processing code, can simulate all the time-dependent coincidence distributions measured by NMIS. In particular, the simulations evaluate the time-dependent coincidence distributions between detectors for plutonium samples having mass 2 and 4 kg, in metal and oxide form. This work shows that the time-dependent coincidence distributions between two scintillators measured by NMIS can be used …

Proton therapy is a treatment modality of increasing utility in clinical radiation oncology mostly because its dose distribution conforms more tightly to the target volume than x-ray radiation therapy. One important feature of proton therapy is that it produces a small amount of positron-emitting isotopes along the beam-path through the non-elastic nuclear interaction of protons with target nuclei such as {sup 12}C, {sup 14}N, and {sup 16}O. These radioisotopes, mainly {sup 11}C, {sup 13}N and {sup 15}O, allow imaging the therapy dose distribution using positron emission tomography (PET). The resulting PET images provide a powerful tool for quality assurance of the treatment, especially when treating inhomogeneous organs such as the lungs or the head-and-neck, where the calculation of the dose distribution for treatment planning is more difficult. This paper uses Monte Carlo simulations to predict the yield of positron emitters produced by a 250 MeV proton beam, and to simulate the productions of the image in a clinical PET scanner.

We are developing a computer code, ORBIT, specifically for beam dynamics calculations in high-intensity rings. Our approach allows detailed simulation of realistic accelerator problems. ORBIT is a particle-in-cell tracking code that transports bunches of interacting particles through a series of nodes representing elements, effects, or diagnostics that occur in the accelerator lattice. At present, ORBIT contains detailed models for strip-foil injection including painting and foil scattering; rf focusing and acceleration; transport through various magnetic elements; longitudinal and transverse impedances; longitudinal, transverse, and three-dimensional space charge forces; collimation and limiting apertures; and the calculation of many useful diagnostic quantities. ORBIT is an object-oriented code, written in C++ and utilizing a scripting interface for the convenience of the user. Ongoing improvements include the addition of a library of accelerator maps, BEAMLINE/MXYZPTLK the introduction of a treatment magnet errors and fringe fields; the conversion of the scripting interface to the standard scripting language, Python; and the parallelization of the computations using MPI. The ORBIT code is an open source, powerful, and convenient tool for studying beam dynamics in high-intensity rings.

A proposal for an experiment to detect and measure with an array infrared detector either the infrared radiation from the beam-beam coherent bremsstrahlung or from the synchrotron light from the edge effect of large DX RHIC magnet is described. Predictions for the 100 GeV/nucleon gold and 250 GeV proton signals from both bremsstrahlung and synchtrotron radiation magnet edge effect are shown.

The initial performance goal for the SNS compressor ring is 1.4 MW with 1.0 GeV linac beam. During the design phase many considerations and provisions have been made to allow progressive increase in power level of the ring, ultimately to 3.0 MW and beyond after years of improvements. The most important provision for future higher power operation is an increase in beam energy from 1.0 to 1.3 GeV. Other possible upgrades covered in this report include ion source current, new stripper foil material, injection and extraction systems, transverse damper, barrier cavity, and electron clearing to avoid e-p instability.

The most demanding requirement in the design of the SNS accelerator chain is to keep the accelerator complex under hands-on maintenance. This requirement implies a hard limit for residual radiation below 100 mrem/hr at one feet from the vacuum pipe and four hours after shutdown for hundred days of normal operation. It has been shown by measurements as well as simulation [l] that this limit corresponds to 1-2 Watts/meter average beam losses. This loss level is achievable all around the machine except in specific areas where remote handling will be necessary. These areas have been identified and correspond to collimation sections and dumps where a larger amount of controlled beam loss is foreseen. Even if the average level of loss is kept under 1 W/m, there are circumstances under which transient losses occur in the machine. The prompt radiation or potential damage in the accelerator components can not be deduced from an average beam loss of 1 W/m. At the same time, controlled loss areas require a dedicated study to clarify the magnitude and distribution of the beam loss. From the front end to the target, we have estimated the most probable locations for transient losses and given an estimate …

The Spallation Neutron Source (SNS) is designed to reach an average proton beam power of 1.4 MW for pulsed neutron production. This paper summarizes design aspects and physical challenges to the project.

Ionization cooling is an essential component of a neutrino factory or a muon collider. Ionization cooling in the transverse dimensions is reasonably straightforward, and has been incorporated in published neutrino factory studies. Achieving cooling in the longitudinal dimensions is more difficult, but has the potential to greatly improve the performance of neutrino factories, and is essential to muon colliders. Much progress has recently been made in describing ring cooling lattices which achieve cooling in all three phase space planes, and in the design of the required, but difficult, injection systems. Ring cooling lattices also have the potential of significantly reduced cost compared to single-pass cooling systems with comparable performance. We will present some recent lattice designs, describing their theory, features, and performance, including injection and extraction systems.

The Integrated Materials Management System, when fully implemented, will provide the Y-12 National Security Complex with advanced inventory information and analysis capabilities and enable effective assessment, forecasting and management of nuclear materials, critical non-nuclear materials, and certified supplies. These capabilities will facilitate future Y-12 stockpile management work, enhance interfaces to existing National Nuclear Security Administration (NNSA) corporate-level information systems, and enable interfaces to planned NNSA systems. In the current national nuclear defense environment where, for example, weapons testing is not permitted, material managers need better, faster, more complete information about material properties and characteristics. They now must manage non-special nuclear material at the same high-level they have managed SNM, and information capabilities about both must be improved. The full automation and integration of business activities related to nuclear and non-nuclear materials that will be put into effect by the Integrated Materials Management System (IMMS) will significantly improve and streamline the process of providing vital information to Y-12 and NNSA managers. This overview looks at the kinds of information improvements targeted by the IMMS project, related issues, the proposed information architecture, and the progress to date in implementing the system.

Conventionally, the multiple and single particle scattering in a storage ring are considered to be independent. Such an approach is simple and often yields sufficiently accurate results. Nevertheless, there is a class of problems where such an approach is not adequate and the single and multiple scattering need to be considered together. This can be achieved by solving an integro-differential equation for the particle distribution function, which correctly treats particle Coulomb scattering in the presence of betatron motion. A derivation of the equation is presented in the article. A numerical solution for one practical case is also considered.