In this paper we present a detailed and unified theoretical treatment of secondary electron cascades that follow the absorption of an X-ray photon. A Monte Carlo model has been constructed that treats in detail the evolution of electron cascades induced by photoelectrons and by Auger electrons following inner shell ionizations. Detailed calculations are presented for cascades initiated by electron energies between 0.1-10 keV. The present paper expands our earlier work by extending the primary energy range, by improving the treatment of secondary electrons, especially at low electron energies, by including ionization by holes, and by taking into account their coupling to the crystal lattice. The calculations describe the three-dimensional evolution of the electron cloud, and monitor the equivalent instantaneous temperature of the free-electron gas as the system cools. The dissipation of the impact energy proceeds predominantly through the production of secondary electrons whose energies are comparable to the binding energies of the valence (40-50 eV) and of the core electrons (300 eV). The electron cloud generated by a 10 keV electron is strongly anisotropic in the early phases of the cascade (t {le} 1 fs). At later times, the sample is dominated by low energy electrons, and these are scattered …

Experiments are described that have increased understanding of the transport and stability physics that set the H-mode edge pedestal width and height, determine the onset of Type-I edge localized modes (ELMs), and produce the nonlinear dynamics of the ELM perturbation in the pedestal and scrape-off layer (SOL). Predictive models now exist for the n{sub e} pedestal profile and the p{sub e} height at the onset of Type-I ELMs, and progress has been made toward predictive models of the T{sub e} pedestal width and nonlinear ELM evolution. Similarity experiments between DIII-D and JET suggested that neutral penetration physics dominates in the relationship between the width and height of the n{sub e} pedestal while plasma physics dominates in setting the T{sub e} pedestal width. Measured pedestal conditions including edge current at ELM onset agree with intermediate-n peeling-ballooning (P-B) stability predictions. Midplane ELM dynamics data show the predicted (P-B) structure at ELM onset, large rapid variations of the SOL parameters, and fast radial propagation in later phases, similar to features in nonlinear ELM simulations.

Optimization of the non-scaling FFAG lattice for the specific application of the muon acceleration with respect to the minimum orbit offsets, minimum path length and smallest circumference is described. The short muon lifetime requires fast acceleration. The acceleration is in this work assumed to be with super-conducting cavities. This sets up a condition of acceleration at the top of the sinusoidal RF wave.

Because of the highly repetitive nature and simple cell structure of FFAG lattices, it is possible to automatically design these lattices. In designing an FFAG lattice, one will try to meet certain constraints and then minimize some cost function by varying any remaining free parameters. I will first review previously published work on optimized FFAG design. Then I will describe recent advances in the understanding of linear non-scaling FFAG design that have come from these optimization techniques. I will describe how the lattice designs depend on some input parameters to the design. Finally, I will present a set of FFAG lattices that are optimized for muon acceleration using these techniques.

In an earlier report they have reviewed four major rules to design the lattice of Fixed-Field Alternating-Gradient (FFAG) accelerators. One of these rules deals with the search of the Adjusted Field Profile, that is the field non-linear distribution along the length and the width of the accelerator magnets, to compensate for the chromatic behavior, and thus to reduce considerably the variation of betatron tunes during acceleration over a large momentum range. The present report defines the method for the search of the Adjusted Field Profile.

There are two major issues that are to be confronted in the design of a Fixed-Field Alternating-Gradient (FFAG) accelerator, namely: (1) the stability of motion over the large momentum range needed for the beam acceleration, and (2) the compactness of the trajectories over the same momentum range to limit the dimensions of the magnets. There are a numbers of rules that need to be followed to resolve these issues. In particular, the magnet arrangement in the accelerator lattice and the distribution of the bending and focusing fields are to be set properly in accordance with these rules. In this report they describe four of these rules that ought to be applied for the optimum design of a FFAG accelerator, especially in the case of proton beams.

We present seven separate Chandra observations of the 2001 superoutburst of WZ Sge. The high-energy outburst was dominated by intense EUV emission lines, which we interpret as boundary layer emission scattered into our line of sight in an accretion disc wind. The direct boundary layer emission was hidden from view, presumably by the accretion disc. The optical outburst orbital hump was detected in the EUV, but the common superhump was not, indicating a geometric mechanism in the former and a dissipative mechanism in the latter. X-rays detected during outburst were not consistent with boundary layer emission and we argue that there must be a second source of X-rays in dwarf novae in outburst.

Proton accelerators producing beam powers of up to 1 MW are presently either operating or under construction and designs for Multi-Megawatt facilities are being developed. High beam power has applications in the production of high intensity secondary beams of neutrons, muons, kaons and neutrinos as well as in nuclear waste transmutation and accelerator-driven sub-critical reactors. Each of these applications has additional requirements on beam energy and duty cycle. This paper will review how present designs for future Multi-Megawatt facilities meet these requirements and will also review the experience with present high power facilities.

A gamma-ray spectrometer (GRS) has been built and delivered to the Mercury MESSENGER spacecraft which launched on August 3, 2004, from Cape Canaveral, Florida. The GRS, a part of seven scientific instruments on board MESSENGER, is based on a coaxial high-purity germanium detector. Gamma-ray detectors based on germanium have the advantage of providing excellent energy resolution, which is critical to achieving the science goals of the mission. However, germanium has the disadvantage that it must operate at cryogenic temperatures (typically {approx}80 K). This requirement is easy to satisfy in the laboratory but difficult near Mercury, which has an extremely hot thermal radiation environment. To cool the detector, a Stirling cycle mechanical cooler is employed. In addition, radiation and conduction techniques a are used to reduce the GRS heat load. Before delivering the flight sensor, a complete thermal prototype was built and tested. The results of these test, including thermal design, radiative and conductive heat loads, and cooler performance are described.

The antiproton beam in the 1.5-15 GeV storage ring HESR., in part designed at Juelich for the FAIR complex at GSI, will contain a section with electron cooling. The electron beam in this section generates a radial electric field that produces a marked defocusing of the antiprotons in both transverse planes. This note presents a model of the cooling beam and describes the corresponding perturbation of the optics.

The paper discusses the issues, the consequences and the methods for controlling the edge effects caused by particles entering and leaving magnets with trajectories at non-vanishing angles with the edges in FFAG accelerators made of Non-Scaling Lattices.

While ''greenhouse gases'' have been the focus of climate change research for a number of years, DOE's ''Aerosol Initiative'' is now examining how aerosols (small particles of approximately micron size) affect the climate on both a global and regional scale. Scientists in the Atmospheric Science Division at Lawrence Livermore National Laboratory (LLNL) are using NERSC's IBM supercomputer and LLNL's IMPACT (atmospheric chemistry) model to perform simulations showing the historic effects of sulfur aerosols at a finer spatial resolution than ever done before. Simulations were carried out for five decades, from the 1950s through the 1990s. The results clearly show the effects of the changing global pattern of sulfur emissions. Whereas in 1950 the United States emitted 41 percent of the world's sulfur aerosols, this figure had dropped to 15 percent by 1990, due to conservation and anti-pollution policies. By contrast, the fraction of total sulfur emissions of European origin has only dropped by a factor of 2 and the Asian emission fraction jumped six fold during the same time, from 7 percent in 1950 to 44 percent in 1990. Under a special allocation of computing time provided by the Office of Science INCITE (Innovative and Novel Computational Impact on Theory …

Climate and the global carbon cycle are a tightly coupled system where changes in climate affect exchange of atmospheric CO{sup 2} with the land biosphere and the ocean, and vice-versa. In particular, the response of the land biosphere to the ongoing increase in atmospheric CO{sup 2} is not well understood. To evaluate the approximate upper and lower limits of land carbon uptake, we perform simulations using a comprehensive climate-carbon model. In one case the land biosphere is vigorously fertilized by added CO{sup 2} and sequesters carbon throughout the 21st century. In a second case, CO{sup 2} fertilization saturates in year 2000; here the land becomes an additional source of CO{sup 2} by 2050. The predicted atmospheric CO{sup 2} concentration at year 2100 differs by 40% between the two cases. We show that current uncertainties preclude determination of whether the land biosphere will amplify or damp atmospheric CO{sup 2} increases by the end of the century.

Nonlinear simulations of plasma discharges in the Sustained Spheromak Physics Experiment demonstrate the role of transient effects in establishing a toroidal magnetic structure that confines internal energy. The magnetohydrodynamics-based model includes collisional anisotropic thermal energy transport and temperature-dependent electrical resistivity that are realistic for the open-field regions of the plasma. The modeling shows that while dynamo activity is responsible for generating net poloidal flux during the formation current pulse, it is insufficient to sustain the configuration during the quiescent phase. The second current pulse improves confinement by keeping the q-profile from falling significantly below the value of 1/2, thereby suppressing resonant m=1, n=2 magnetohydrodynamic activity. Direct comparisons of laboratory observations and simulation results validate essential aspects of the model.

Wick's limit is an inequality that relates the zero-degree differential elastic scattering cross section to the total cross section. The deviation of Wick's limit from an exact equality is small over a wide range of incident energies and target masses. Under these circumstances we show that Wick's limit can be used to correlate the uncertainties in the two terms of the reaction (nonelastic) cross section expressed as the difference between the total and angle-integrated elastic cross sections. When suitable elastic angular distributions are available, we show that the reaction cross section may be obtained with small errors (typically 1.5-3%). Examples are shown for {sup 208P}b, {sup 54-56}Fe, {sup 232}Th, and {sup 238}U.

The Rare Isotope Accelerator will produce many isotopes at never before seen rates. This will allow for the first time measurements on isotopes very far from stability and new measurement opportunities for unstable nuclei near stability. In fact, the production rates are such that it should be possible to collect 10 micrograms of many isotopes with a half-life of 1 day or more. This ability to make targets of short-lived nuclei enables the possibility of making neutron cross-section measurements important to the astrophysics and the stockpile stewardship communities. But to fully realize this opportunity, the appropriate infrastructure must be included at the RIA facility. This includes isotope harvesting capabilities, radiochemical areas for processing collected material, and an intense, ''mono-energetic'', tunable neutron source. As such, we have been developing a design for neutron source facility to be included at the RIA site. This facility would produce neutrons via intense beams of deuterons and protons on a variety of targets. The facility would also include the necessary radiochemical facilities for target processing. These infrastructure needs will be discussed in addition to the methods that would be employed at RIA for measuring these neutron cross-sections.

It has been proposed recently to upgrade the Alternating-Gradient Synchrotron (AGS) of Brookhaven National Laboratory (BNL) to an average proton beam power of one MWatt at the top energy of 28 GeV. This is to be accomplished primarily by raising the AGS repetition rate from the present {approx} 1/3 to 2.5 pulses per second, and by a relatively modest increase of beam intensity from the present 0.7 to about 1.0 x 10{sup 14} protons per cycle. The present injector, the 1.5 GeV Booster, has a circumference a quarter of that of the AGS, and four successive beam pulses are required for a complete fill of the AGS. The filling time at injection is thus at least 0.5 seconds, and it ought to be eliminated if one desires to shorten the AGS cycle period. Moreover, holding the beam for such a long period of time during injection causes its quality to deteriorate and beam losses. This report is the summary of the results of a feasibility study of a 1.5 GeV Fixed-Field Alternating-Gradient (FFAG) Accelerator as a new possible injection to the AGS.

Trivalent cerium ions form the luminescence centers in several important families of scintillation materials including the rare earth oxyorthosilicates, pyrosilicates, and aluminates. When comparing the experimentally determined scintillation properties of cerium-doped scintillators to theoretical models of scintillation mechanisms, there is often speculation regarding the fraction of the total cerium that exists in the radiative trivalent charge state (Ce{sup 3+}) rather than the non-radiative tetravalent state (Ce{sup 4+}). Until now, however, no technique has been developed to quantitatively measure both Ce{sup 3+} and Ce{sup 4+}. We report here for the first time direct measurements of Ce{sup 3+} and Ce{sup 4+} in Lu{sub 2}SiO{sub 5}:Ce scintillators. Synchrotron radiation was used to measure the x x-ray absorption on the M{sub 4} and M{sub 5} edges of Ce, and the results were compared to model samples of Ce{sup 3+} (Ce{sub 2}O{sub 3}) and Ce{sup 4+} (CeO{sub 2}) which provided clear signatures of the two charge states. The spectra were obtained with a high-resolution superconducting tunnel junction spectrometer on beamline 4.0.2 at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The results clearly show 100% Ce{sup 3+}, independent of light yield and sample coloration. Therefore, energy migration to the luminescence centers appears to …

This paper is the summary of a feasibility study of a Fixed-Field Alternating-Gradient (FFAG) Accelerator for Protons in the one-to-few GeV energy range, and average beam power of several MWatt. The example they have adopted here is a beam energy of 1 GeV and an average power of 10 MWatt, but of course the same design approach can be used with other beam parameters. The design principles, merits and limitations of the FFAG accelerators have been described previously. In particular, more advanced techniques to minimize magnet dimension and field strength have been recently proposed. The design makes use of a novel concept by which it is possible to cancel chromatic effects, thus making betatron tunes and functions independent of the particle momentum, with an Adjusted Field Profile. The example given here assumes a pulsed mode of operation at the repetition rate of 1.0 kHz.

The Madden-Julian Oscillation (MJO) dominates tropical variability on timescales of 30-70 days. During the boreal winter/spring it is manifested as an eastward propagating disturbance, with a strong convective signature over the eastern hemisphere. The space-time structure of the MJO is analyzed using simulations with the ECHAM4 atmospheric general circulation model run with observed monthly mean sea-surface temperatures, and coupled to three different ocean models. The coherence of the eastward propagation of MJO convection is sensitive to the ocean model to which ECHAM4 is coupled. For ECHAM4/OPYC and ECHO-G, models for which {approx}100 years of daily data is available, Monte Carlo sampling indicates that their metrics of eastward propagation are different at the 1% significance level. The flux-adjusted coupled simulations, ECHAM4/OPYC and ECHO-G, maintain a more realistic mean-state, and have a more realistic MJO simulation than the non-adjusted SINTEX coupled runs. The SINTEX model exhibits a cold bias in Indian Ocean and tropical West Pacific Ocean sea-surface temperature of {approx}0.5 C. This cold bias affects the distribution of time-mean convection over the tropical Eastern Hemisphere. Furthermore, the eastward propagation of MJO convection in this model is not as coherent as in the two models that used flux adjustment or compared to …