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EFFECT OF PARTICLE SOURCES ON THE STRUCTURE OF THE H-MODE PEDESTAL

Description: Techniques of dimensional analysis have been applied to deuterium and hydrogen plasmas in DIII-D to test the postulate that the edge particle source plays a role in forming the edge H-mode density profile. These experiments show that the pedestal density scale length is typically a factor of two to three larger in hydrogen plasmas than in deuterium plasmas with dimensionally similar ion parameters. These results are in agreement with the postulate [1,2] that the density scale length is primarily determined by the local particle source, rather than by the shape of a hypothetical particle transport barrier. The electron temperature scale length displays a similar trend, albeit with a weaker density dependence. Thus the pedestal pressure gradient scale length is larger in hydrogen. It is also observed that the frequency of a coherent mode, localized within the pedestal, increases with the local density (i.e. inversely with the local density scale length) irrespective of the working gas species. This frequency is a factor of two lower in a hydrogen discharge than in a dimensionally similar deuterium plasma, a result which cannot be explained solely in terms of plasma physics variables.
Date: July 1, 2002
Creator: MAHDAVI, M.A.; R.J.GROEBNER; LEONARD, A.W.; LUCE, T.C.; McKEE, G.R.; MOYER, R.A. et al.
Partner: UNT Libraries Government Documents Department

A proton driver for the muon collider source with a tunable momentum compaction lattice

Description: The future Muon Collider will have a luminosity of the order of 10{sup 35} cm{sup {minus}2{minus}1} during 1,000 turns when the muons decay. This requires 10{sup 12} muons per bunch. The muon source is a 30 GeV proton driver with 2.5 10{sup 13} protons per pulse. The proton bunch length should be of the order of 1 ns. Short bunches could be created by a tunable momentum compaction lattice which would bring the momentum compaction to zero in a short time. This isochronous conduction would allow bunches to shear and become very short in time. The authors present a lattice where the momentum compaction is a tunable parameter at fixed horizontal and vertical betatron tunes. The values of the maxima of the dispersion function are kept small. They examine two kinds of lattices, with combined function as well as normal dipole and quadrupole magnets.
Date: July 1, 1997
Creator: Trbojevic, D.; Brennan, J.M.; Courant, E.D.; Roser, T.; Peggs, S.; Ng, K.Y. et al.
Partner: UNT Libraries Government Documents Department

Gyrokinetic Calculations of Microinstabilities and Transport During RF H-Modes on Alcator C-Mod

Description: Physics understanding for the experimental improvement of particle and energy confinement is being advanced through massively parallel calculations of microturbulence for simulated plasma conditions. The ultimate goal, an experimentally validated, global, non-local, fully nonlinear calculation of plasma microturbulence is still not within reach, but extraordinary progress has been achieved in understanding microturbulence, driving forces and the plasma response in recent years. In this paper we discuss gyrokinetic simulations of plasma turbulence being carried out to examine a reproducible, H-mode, RF heated experiment on the Alcator CMOD tokamak3, which exhibits an internal transport barrier (ITB). This off axis RF case represents the early phase of a very interesting dual frequency RF experiment, which shows density control with central RF heating later in the discharge. The ITB exhibits steep, spontaneous density peaking: a reduction in particle transport occurring without a central particle source. Since the central temperature is maintained while the central density is increasing, this also suggests a thermal transport barrier exists. TRANSP analysis shows that ceff drops inside the ITB. Sawtooth heat pulse analysis also shows a localized thermal transport barrier. For this ICRF EDA H-mode, the minority resonance is at r/a * 0.5 on the high field side. There is a normal shear profile, with q monotonic.
Date: June 18, 2002
Creator: Redi, M.H.; Fiore, C.; Bonoli, P.; Bourdelle, C.; Budny, R.; Dorland, W.D. et al.
Partner: UNT Libraries Government Documents Department

Longitudinal Density Modulation and Energy Conversion in Intense Beams

Description: Density modulation of charged particle beams may occur as a consequence of deliberate action, or may occur inadvertently because of imperfections in the particle source or acceleration method. In the case of intense beams, where space charge and external focusing govern the beam dynamics, density modulation may under some circumstances be converted to velocity modulation, with a corresponding conversion of potential energy to kinetic energy. Whether this will occur depends on the properties of the beam and the initial modulation. This paper describes the evolution of discrete and continuous density modulations on intense beams, and discusses three recent experiments related to the dynamics of density-modulated electron beams.
Date: February 17, 2006
Creator: Harris, J; Neumann, J; Tian, K & O'Shea, P
Partner: UNT Libraries Government Documents Department

PAPERS PRESENTED AT THE EIGHTH ANNUAL MEETING ON BIO-ASSAY AND ANALYTICAL CHEMISTRY, AUGUSTA, GEORGIA, OCTOBER 18-19, 1962

Description: Nine papers are included which treat the determination of cesium, tritium, americium-241, plutonium, thoron, and other radionuclides under a variety of conditions. One treats the preparation of standard alpha sources. Separate abstracts were prepared for six of the papers; the reraaining three papers were previously abstracted in NSA. (D.L.C.)
Date: October 31, 1963
Partner: UNT Libraries Government Documents Department

TRAJECTORIES FOR A RECTANGULAR MAGNET WITH UNIFORM FIELD

Description: To aid in orientation of a hodoscope system using a rectangular magnet with a uniform field, projections of the trajectory of particles in the horizontal and ventical planes are calculated approximately. Fringing field effects are represented by adding a correction to the length of the magnet and assuming the field to be uniform over the total effective length. The assumption that the source lies in the median plane of the magnet is also used in treating the vertical motion. (D.C.W.)
Date: February 1, 1963
Creator: Sternheimer, R.M.
Partner: UNT Libraries Government Documents Department

VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific

Description: The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean's 'twilight zone' (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3 week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiency (T{sub eff}) of particulate organic carbon (POC), POC flux 500/150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150 m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500 m fluxes to deep moored traps, both sites lose about half of the sinking POC by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking ...
Date: June 10, 2008
Creator: Buesseler, K.O.; Trull, T.W.; Steinberg, D.K.; Silver, M.W.; Siegel, D.A.; Saitoh, S.-I. et al.
Partner: UNT Libraries Government Documents Department

Report of the Snowmass T4 working group on particle sources: Positron sources, anti-proton sources and secondary beams

Description: This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 was charged with examining the most challenging aspects of positron sources for linear colliders and antiproton sources for proton-antiproton colliders, and the secondary beams of interest to the physics community that will be available from the next generation of high-energy particle accelerators. The leading issues, limiting technologies, and most important R and D efforts of positron production, antiproton production, and secondary beams are discussed in this paper. A listing of T4 Presentations is included.
Date: December 5, 2002
Creator: al., N. Mokhov et
Partner: UNT Libraries Government Documents Department

RF parameter curves for a proton driver synchrotron

Description: High average beam power proton synchrotrons in the medium energy range are under consideration at several laboratories for intense and specialized secondary particle sources like muon colliders and {nu} factories. A 12-16 GeV machine with a 15 Hz cycle and 3 {center_dot} 10{sup 13} p/pulse capability called the Proton Driver (PD) has been studied as a replacement for the Fermilab Booster and as a base for future facilities.[1] A staged development is proposed, initially using 20 modified 53 MHz Booster cavities in 12 GeV operation.[2] A second stage would allow 16 GeV top energy using a 7.5 MHz rf system consisting of 100 15 kV low-Q cavities.[3] This paper discusses the choices of rf system parameters made in the design study. The limited number of existing Booster cavities has led to consideration for stage 1 of an inductive insert in the ring to aid initial beam capture by compensating longitudinal space charge, an admittedly speculative expedient requiring followup with further calculation and some beam experiments. This report is one of nineteen papers at this conference by members of the Proton Driver design team; it relies on these others to help establish the general context.
Date: July 12, 2001
Creator: James A. MacLachlan, Z. Qian and J.E. Griffin
Partner: UNT Libraries Government Documents Department

Muon collider overview: Progress and future plans

Description: Besides continued work on the parameters of a 3--4 and 0.5 TeV center of mass (CoM) collider, many studies are now concentrating on a machine near 100 GeV (CoM) that could be a factor for the s-channel production of Higgs particles. The authors mention the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ({pi} {r_arrow} {mu}{nu}{sub {mu}}) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. The authors also mention theoretical and experimental R and D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This note is a summary of a report updating the progress on the R and D since the Feasibility Study of Muon Colliders presented at the Workshop Snowmass `96.
Date: June 1998
Creator: Palmer, R.; Sessler, A.; Tollestrup, A.; Gallardo, J. & Collaboration, Muon Collider
Partner: UNT Libraries Government Documents Department

Environment, safety, and health considerations for a neutrino source based on a muon storage ring

Description: The Neutrino Source presents a number of challenges in the general area of environment, safety, and health. It is the intent of this paper to identify these challenges and make a preliminary, but not detailed assessment of how they might be addressed and of their potential impact on the project. Some of the considerations which must be taken into account are very similar to those that have been encountered and solved during the construction and operation of other facilities at Fermilab and at similar laboratories elsewhere in the US and worldwide. Other considerations have not been encountered previously in connection with the construction and operation of accelerator laboratories. These novel issues will require particular attention as such a project proceeds to assure their timely resolution in a manner that is cost-effective and that meets the approval of the public. In this paper, both the conventional and the novel issues are discussed, with more emphasis on the latter. It is concluded here that with adequate planning in the design stages, these problems can be adequately addressed in a manner that merits the support of the Laboratory, the Department of Energy, and the public. An abbreviated version of this paper appears as Chapter 14 in the report of a recent feasibility study (Ho 00)and the figures have come from that work.
Date: May 15, 2000
Creator: Cossairt, J. Donald
Partner: UNT Libraries Government Documents Department

Focused Ion beam source method and Apparatus

Description: A focused ion beam having a cross section of submicron diameter, a high ion current, and a narrow energy range is generated from a target comprised of particle source material by laser ablation. The method involves directing a laser beam having a cross section of critical diameter onto the target, producing a cloud of laser ablated particles having unique characteristics, and extracting and focusing a charged particle beam from the laser ablated cloud. The method is especially suited for producing focused ion beams for semiconductor device analysis and modification.
Date: August 17, 1998
Creator: Pellin, Michael J.; Lykke, Keith R. & Lill, Thorsten B.
Partner: UNT Libraries Government Documents Department

Edge Recycling and Heat Fluxes in L- and H-mode NSTX Plasmas

Description: Introduction Edge characterization experiments have been conducted in NSTX to provide an initial survey of the edge particle and heat fluxes and their scaling with input power and electron density. The experiments also provided a database of conditions for the analyses of the NSTX global particle sources, core fueling, and divertor operating regimes.
Date: August 5, 2003
Creator: Soukhanovskii, V.A.; Maingi, R.; Raman, R.; Kugel, H.; LeBlanc, B.; Roquemore, A.L. et al.
Partner: UNT Libraries Government Documents Department

Core Fueling and Edge Particle Flux Analysis in Ohmically and Auxiliary Heated NSTX Plasmas

Description: The Boundary Physics program of the National Spherical Torus Experiment (NSTX) is focusing on optimization of the edge power and particle flows in b * 25% L- and H-mode plasmas of t {approx} 0.8 s duration heated by up to 6 MW of high harmonic fast wave and up to 5 MW of neutral beam injection. Particle balance and core fueling efficiencies of low and high field side gas fueling of L-mode homic and NBI heated plasmas have been compared using an analytical zero dimensional particle balance model and measured ion and neutral fluxes. Gas fueling efficiencies are in the range of 0.05-0.20 and do not depend on discharge magnetic configuration, density or poloidal location of the injector. The particle balance modeling indicates that the addition of HFS fueling results in a reversal of the wall loading rate and higher wall inventories. Initial particle source estimates obtained from neutral pressure and spectroscopic measurements indicate that ion flux into the divertor greatly exceeds midplane ion flux from the main plasma, suggesting that the scrape-off cross-field transport plays a minor role in diverted plasmas. Present analysis provides the basis for detailed fluid modeling of core and edge particle flows and particle confinement properties of NSTX plasmas. This research was supported by the U.S. Department of Energy under contracts No. DE-AC02-76CH03073, DE-AC05-00OR22725, and W-7405-ENG-36.
Date: June 12, 2002
Creator: Soukhanovskii, V.A.; Maingi, R.; Raman, R.; Kugel, H.W.; LeBlanc, B.P.; Roquemore, L. et al.
Partner: UNT Libraries Government Documents Department

Neutron generator instrumentation at the Department 2350 Neutron Generator Test Facility

Description: The computer and waveform digitizing capability at the test facility has allowed several changes in the techniques used to test neutron generators. These changes include methods used to calibrate the instrumentation and changes in the operation of the test facility. These changes have increased the efficiency of the test facility as well as increasing both timing and amplitude accuracy of neutron generator waveforms.
Date: June 1, 1979
Creator: Bryant, T.C. & Mowrer, G.R.
Partner: UNT Libraries Government Documents Department

Advanced Neutron Source: The designer's perspective

Description: The Advanced Neutron Source (ANS) is a research facility based on a 350 MW beam reactor, to be brought into service at the Oak Ridge National Laboratory at the end of the century. The primary objective is to provide high-flux neutron beams and guides, with cold, thermal, hot, and ultra-cold neutrons, for research in many fields of science. Secondary objectives include isotopes production, materials irradiation and activation analysis. The design of the ANS is strongly influenced by the historical development of research and power reactor concepts, and of the regulatory infrastructure of the Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC). Current trends in reactor safety also impact the climate for the design of such a reactor.
Date: January 1, 1990
Creator: Peretz, F.J.
Partner: UNT Libraries Government Documents Department

A REVIEW OF GLOVE BOX CONSTRUCTION AND EXPERIMENTATION

Description: A series of fires and explosions in U. S. Atomic Energy Commission facilities handling alpha -active materiais during the last five years resulted in reconsideration of safety problems associated with glove boxes and other equipment used to contain these materials. The literature on construction and operation of glove boxes for work with toxic inorganic materials not requiring biological shielding is reviewed as a contribution to this re-examination, with special emphasis on methods and equipment for working safely with plutonium and other alpha -active materials. An effort was made to point out the direction of current trends in this field. Detailed discussions of glove box designs and methods of experimentation in these enclosures are not included in this report but sufficient information is furnished for finding needed details in the referenced material. Methods for the detection and measurement of alpha -active materials and of impurities in controlled atmospheres are discussed. In addition, the literature on controlled atmosphere enclosures, glove boxes for non- toxic inorganic materials, and the technique of experimenting with such enclosures is reviewed. Some previously unpublished developments are reported. (auth)
Date: June 14, 1961
Creator: Barton, C.J.
Partner: UNT Libraries Government Documents Department

GROUNDING OF BETA SOURCES BY AN AUXILIARY ALPHA SOURCE

Description: A Po/sup 210/ source was used to furnish a reliab1e ground for both electron and positron sources. This was done to prevent the electron and positron sources from charging during BETA spectral studies in magnetic lens spectrometers. An approximately 20- mu c Po/sup 210/ source was placed 1.2 in. behind a 4- mu c Na/sup 2 / 2>s positron emitter backed by 20- mu g/cm/sup 2/ Formvar in the spectrometer; this arrangement resulted in a charging rate decrease of approximately 80%. When the source was placed 0.5 in. away, no charging was detectable over a period of more than one week. The discharge is attributed mainly to the loss of electrons from the source and backing caused by ionization of alpha particles since few alpha particles are stopped near the source. (B.O.G.)
Date: December 1, 1960
Creator: Nichols, R.T. & Jensen, E.N.
Partner: UNT Libraries Government Documents Department

LOCA mitigation studies for the advanced neutron source: The inertial flow diode concept

Description: This paper documents a study of the consequences of loss of coolant accidents in the Advanced Neutron Source reactor, and it introduces the concept of an inertial flow diodes to mitigate the effect of large cold leg breaks. 2 refs., 1 fig.
Date: January 1, 1991
Creator: Khayat, M.I.; Perez, R.B. (Tennessee Univ., Knoxville, TN (USA)) & March-Leuba, J. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department

Optimization of the particle pusher in a diode simulation code

Description: The particle pusher in Sandia's particle-in-cell diode simulation code has been rewritten to reduce the required run time of a typical simulation. The resulting new version of the code has been found to run up to three times as fast as the original with comparable accuracy. The cost of this optimization was an increase in storage requirements of about 15%. The new version has also been written to run efficiently on a CRAY-1 computing system. Steps taken to affect this reduced run time are described. Various test cases are detailed.
Date: September 1, 1979
Creator: Theimer, M.M. & Quintenz, J.P.
Partner: UNT Libraries Government Documents Department