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RF properties of periodic accelerating structures for linear colliders

Description: With the advent of the SLAC electron-positron linear collider (SLC) in the 100 GeV center-of-mass energy range, research and development work on even higher energy machines of this type has started in several laboratories in the United States, Europe, the Soviet Union and Japan. These linear colliders appear to provide the only promising approach to studying e/sup /plus//e/sup /minus// physics at center-of-mass energies approaching 1 TeV. This thesis concerns itself with the study of radio frequency properties of periodic accelerating structures for linear colliders and their interaction with bunched beams. The topics that have been investigated are: experimental measurements of the energy loss of single bunches to longitudinal modes in two types of structures, using an equivalent signal on a coaxial wire to simulate the beam; a method of canceling the energy spread created within a single bunch by longitudinal wakefields, through appropriate shaping of the longitudinal charge distribution of the bunch; derivation of the complete transient beam-loading equation for a train of bunches passing through a constant-gradient accelerator section, with application to the calculation and minimization of multi-bunch energy spread; detailed study of field emission and radio frequency breakdown in disk-loaded structures at S-, C- and X-band frequencies under extremely high-gradient conditions, with special attention to thermal effects, radiation, sparking, emission of gases, surface damage through explosive emission and its possible control through RF-gas processing. 53 refs., 49 figs., 9 tabs.
Date: July 1, 1989
Creator: Wang, J.W.
Partner: UNT Libraries Government Documents Department

Some problems on rf breakdown in room temperature accelerator structure, a possible criterion

Description: The discussion is confined to high gradient, room-temperature accelerators which have clean well-finished cavity surfaces and good vacuum conditions. Breakdown-initiating mechanisms due to ''cold'' field electron emission occurring at isolated sites on broad-area cavity surfaces, where the field is enhanced, are described. The influences of an alternating field and transition time tunneling are taken into account. The thermal instability resulting in vacuum voltage breakdown is hypothesized to derive a new criterion for room-temperature accelerator structure. 18 refs., 5 figs. (DWL)
Date: April 1, 1986
Creator: Wang, J.W.
Partner: UNT Libraries Government Documents Department

Common transverse feedback damper for two beams during a stacking cycle

Description: During the stacking cycle at a proton-storage ring, it often occurs that coasting and bunched beams coexist, rotating in the same direction. The problem of the two beams oscillating coherently with each other is formulated and discussed. It is demonstrated that when the tune distribution is dominated by the sextupole contribution, one common transverse dipole feedback system is enough to damp both the coasting-beam and the bunched-beam instabilities.
Date: January 1, 1983
Creator: Wang, J.M.
Partner: UNT Libraries Government Documents Department

Environmental impact of a teratogenic actinide: a case study of americium-241

Description: Americium-241 is widely used as a radiation source, but it also has some potential risk if taken into the body. Although the radiotoxicity of americium-241 is small compared to other transuranic actinides, its effects on the reproductive system and on development of the placenta are more damaging than the effects of plutonium-239. A previous report based on a worst-case scenario involving a hypothetical fire accident in a contaminated facility indicated that there could have been a significant impact on nearby residents from a unit release of americium-241 via atmospheric dispersion. However, because the facility is located in a rural region where most drinking water supplies are drawn from private wells, it is believed that deposition of americium-241 from the atmosphere might also have impacts via the groundwater pathway by infiltration of rainwater. In this analysis, a three-dimensional analytical mathematical model is used to assess several aspects of americium-241 contamination of groundwater, including radioactive transformation, advection, dispersion, and soil sorption. Simulation results indicate that no significant radiological impacts would occur to the nearby residents via the groundwater pathway. 15 refs., 2 figs., 2 tabs.
Date: October 16, 1985
Creator: Wang, J. & Yang, J.Y.
Partner: UNT Libraries Government Documents Department

Heat flow and sub-surface temperatures in the Great Valley, California

Description: The Great Valley of California is located between the Coastal Ranges and the Sierra Nevada and geologically is a structural trough with a thick sequence of sediments. Preliminary investigations of heat flow indicates that this region is characterized by a low-to-normal heat flow of 0.6 to 1.3 HFU. A number of shallow holes for water supply and deep holes for oil and gas exploration have been drilled. Temperature measurements were made in most of these holes. Unfortunately, core and drill cuttings were available from only a few holes for thermal conductivity measurements. Here, three new heat-flow values, a gradient map, and an isotherm map of temperatures at 200 meters are presented.
Date: January 1, 1982
Creator: Wang, J. & Munroe, R.J.
Partner: UNT Libraries Government Documents Department

Minimizing the energy spread within a single bunch by shaping its charge distribution

Description: When electrons or positrons in a bunch pass through the periodic structure of a linear accelerator, they leave behind them energy in the form of longitudinal wake fields. The longitudinal fields left behind by early particles in a bunch decrease the energy of later particles. For a linear collider, the energy spread introduced within the bunches by this beam loading effect must be minimized because it limits the degree to which the particles can be focused to a small spot due to chromatic effects in the final focus system. For example, for the SLC, the allowable energy spread is +-0.5%. It has been known for some time that partial compensation of the longitudinal wake field effects can be obtained for any bunch by placing it ahead of the accelerating crest (in space), thereby letting the positive rising sinusoidal field offset the negative beam loading field. The work presented in this report shows that it is possible to obtain complete compensation, i.e., to reduce the energy spread essentially to zero by properly shaping the longitudinal charge distribution of the bunch and by placing it at the correct position on the wave.
Date: June 1, 1984
Creator: Loew, G.A. & Wang, J.
Partner: UNT Libraries Government Documents Department

Environmental assessments for the existing radioactive materials in the Weldon Spring raffinate pits. [Various radioactive residues and wastes from processing of uranium and thorium between 1957 and 1966]

Description: Various radioactive residues (raffinates) and wastes from the processing of uranium and thorium between 1957 and 1966 are stored in four pits at Weldon Spring, Missouri. The US Department of Energy (DOE) plans to stabilize all the contaminated materials on a long-term (more than 1000-year) basis. The effectiveness of stabilization measures are evaluated by estimating radioactive releases under two options: (1) no action, and (2) improved containment using the existing raffinate pits. Two major pathways of radiation exposure are examined: (1) airborne radioactive gases and particulates, and (2) seepage into near-surface groundwater. The relative reductions of releases into the air and groundwater for a reference stabilization option (improved containment) are analyzed using mathematical models for radioactive and particulate gas fluxes and atmospheric dispersion, as well as groundwaterr transport and dispersion. The consequent health risks for nearby individuals and the general public are also evaluated. This study focuses on the migration of radionuclides under existing conditions and evaluates the effectiveness of proposed stabilization measures at the pits. Results indicate that the potential effects to the general public would be insignificant. 22 refs., 2 figs., 6 tabs.
Date: January 1, 1985
Creator: Yang, J.Y. & Wang, J.
Partner: UNT Libraries Government Documents Department

Tranverse beam break up in a periodic linac

Description: The problem of cumulative beam break up in a periodic linac for a general impedance is discussed, with the effects of acceleration included. The transverse equations of motion for a set of identical point like bunches moving along the length of the linac are cast into a simple form using a smooth approximation. This results in a working formula that is used to analyze beam breakup. Explicit expressions for the transverse motion in the case of a single resonance impedance are found using saddle point integration. This is done first with no external focusing, and again in the strong focusing limit.
Date: January 1, 1987
Creator: Decker, G. & Wang, J.M.
Partner: UNT Libraries Government Documents Department

Longitudinal instabilities with a non-harmonic rf potential

Description: We consider the longitudinal instabilities of a bunched beam subject to a non-harmonic rf potential. Assuming the unperturbed bunch to be described by a Maxwell-Boltzmann distribution, our treatment is based upon the linearized Vlasov equation. The formalism developed is exact, and in particular, correctly describes the effect of the dependence on amplitude of the synchrotron oscillation frequency. We discuss the fast blowup limit, and extend Wang and Pellegrini's treatment of the microwave instability to include the case of a non-Gaussian bunch. Next, within the short bunch approximation, we derive the dispersion relation describing the Landau damping of the coupled bunch modes, resulting from the use of a Landau cavity.
Date: January 1, 1983
Creator: Krinsky, S. & Wang, J.M.
Partner: UNT Libraries Government Documents Department

Longitudinal instabilities of long Gaussian bunches

Description: We present an overview of the longitudinal instabilities of Gaussian bunches subject to a harmonic RF potential. Our emphasis is on the behavior of long bunches having lengths greater than the wavelength of the perturbing electromagnetic fields. We exhibit the crossover between the dominance of the synchrotron modes and the coasting-beam-like distortions of the bunch distribution, which occurs as the real or imaginary part of the coherent oscillation frequency becomes large compared to the synchrotron oscillation frequency. For a narrow band impedance the growth rate of the coasting-beam-like modes is determined by the average beam current, and for a broad band impedance the growth rate is determined by the peak current. We discuss the transition between these two regimes by considering the growth rate as a function of the bandwidth of the impedance.
Date: January 1, 1983
Creator: Krinsky, S. & Wang, J.M.
Partner: UNT Libraries Government Documents Department

Theoretical treatment of transverse feedback systems with memory

Description: The differential equation of the dipole moment of coherent oscillations in the presence of a feedback system is derived. The analysis, which starts in the time domain, is extended to the frequency domain; this allows a straightforward derivation of the damping rate for both coasting and bunched beams. The damping rate is expressed in terms of the transfer function of the feedback system and in a general form which takes into account the ..beta..-function and betatron phase modulation along the beam trajectory, the effect of memory arising from the finiteness of the system bandwidth, the effect of the time delay and of the betatron phase advance between detector and kicker. Some examples of the dependence of the damping rate on the feedback parameters are given.
Date: January 1, 1981
Creator: Cornacchia, M. & Wang, J.M.
Partner: UNT Libraries Government Documents Department

AN INNOVATIVE TECHNIQUE FOR THIN FILM INTERFACE TOUGHNESS RESEARCH

Description: A material configuration of central importance in microelectronics, optoelectronics, and thermal barrier coating technology is a thin or thick film of one material deposited onto a substrate of a different material. Fabrication of such a structure inevitably gives rise to stress in the film due to lattice mismatch, differing coefficients of thermal expansion, chemical reactions, or other physical effects. Therefore, in general, the weakest link in this composite system often resides at the interface between the film and substrate. In order to make multi-layered electronic devices and structural composites with long-term reliability, the fracture behavior of the material interfaces must be known. Unfortunately, none of the state-of-the-art testing methods for evaluating interface fracture toughness is fully conformed to fracture mechanics theory, as is evident from the severe scatter in the existing data and the procedure dependence in film/coating evaluation methods. This project is intended to address the problems associated with this deficiency and offers an innovative testing procedure for the determination of interface fracture toughness applicable to coating materials in general. This new approach and the associated bi-material fracture mechanics development proposed for evaluating interface fracture toughness are described herein. The effort includes development of specimen configuration and related instrumentation set-up, testing procedures, postmortem examination, and analytical evaluation. A spiral notch torsion fracture toughness test system was utilized. The objective of the testing procedure described is to enable the development of new coating materials by providing a reliable method for use in assessing their performance. This innovative technology for measuring interface toughness was demonstrated for oxide scales formed on high-temperature alloys of MA956. The estimated energy release rate (in terms of J-integral) at the interface of the alumina scale and MA956 substrate is 3.7 N-m/m{sup 2}, and the estimated equivalent Mode I fracture toughness is 1.1 MPa {radical}m. This innovative ...
Date: November 1, 2004
Creator: Wang, J.J.
Partner: UNT Libraries Government Documents Department

International X-Band Linear Collider Accelerator Structure R&D

Description: For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.
Date: March 4, 2009
Creator: Wang, J. W.
Partner: UNT Libraries Government Documents Department

R&D of Accelerator Structures at SLAC

Description: The research activities for accelerator structures at SLAC are reviewed including the achievement via the main linac design for the Next Linear Collider (NLC), the program adjustment after the decision of the International Linear Collider (ILC) to be based on superconducting technology, and the work progress for the ILC, photon science at SLAC and basic accelerator structure studies.
Date: January 17, 2007
Creator: Wang, J.W.
Partner: UNT Libraries Government Documents Department

TOUGH: a numerical model for nonisothermal unsaturated flow to study waste canister heating effects

Description: The physical processes modeled and the mathematical and numerical methods employed in a simulator for non-isothermal flow of water, vapor, and air in permeable media are briefly summarized. The simulator has been applied to study thermo-hydrological conditions in the near vicinity of high-level nuclear waste packages emplaced in unsaturated rocks. The studies reported here specifically address the question whether or not the waste canister environment will dry up in the thermal phase. 13 references, 8 figures, 2 tables.
Date: December 1, 1983
Creator: Pruess, K. & Wang, J.S.Y.
Partner: UNT Libraries Government Documents Department

Design and test results of kicker units for the positron accumulator ring at the APS

Description: Three fast kicker units have been designed, tested, and installed in the positron accumulator ring (PAR) at the Advanced Photon Source (APS) for beam injection and extraction. The performance of these kicker units has been satisfactory. This presents the design and test results.
Date: June 1, 1995
Creator: Wang, J.
Partner: UNT Libraries Government Documents Department

Hydrologic mechanisms governing fluid flow in partially saturated, fractured, porous tuff at Yucca Mountain

Description: In contrast to the saturated zone where fluid moves rapidly along fractures, the fractures (with apertures large relative to the size of matrix pores) will desaturate first during drainage process and the bulk of fluid flow would be through interconnected pores in the matrix. Within a partially drained fracture, the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture. The residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small. Normal to the fracture surfaces, the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block. A general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions. Results are obtained from an aperture distribution model for fracture saturation, hydraulic conductivity, and effective matrix-fracture flow areas as functions of pressure. Drainage from a fractured tuff column is simulated. The parameters for the simulations are deduced from fracture surface characteristics, spacings and orientations based on core analyses, and from matrix characteristics curve based on laboratory measurements. From the cases simulated for the fractured, porous column with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account, it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties. However, the quasi-steady changes of the fluid flow of a partially saturated, fractured, porous system could be approximately simulated without taking the fractures into account. 22 references, 16 figures.
Date: October 1, 1984
Creator: Wang, J.S.Y. & Narasimhan, T.N.
Partner: UNT Libraries Government Documents Department

GROA AIRBORNE RELEASE DISPERSION FACTOR CALCULATION

Description: The purpose of this document is to calculate airborne release dispersion factors ({chi}/Q) for the surface and subsurface facilities at the Geological Repository Operations Area (GROA). The calculated {chi}/Q values may be used to estimate radiological consequences to workers for potential releases from normal operations and event sequences for License Application. The scope of this document is to provide estimates of {chi}/Q values at potential onsite receptors from facility releases, under normal operating conditions and event sequences.
Date: March 21, 2005
Creator: Wang, J.
Partner: UNT Libraries Government Documents Department

In Situ Field Testing of Processes

Description: The purpose of this Analysis/Model Report (AMR) is to update and document the data and subsequent analyses from ambient field-testing activities performed in underground drifts of the Yucca Mountain Site Characterization Project (YMP). This revision updates data and analyses presented in the initial issue of this AMR. This AMR was developed in accordance with the ''Technical Work Plan for Unsaturated Zone (UZ) Flow and Transport Process Model Report'' and ''Technical Work Plan for UZ Flow, Transport, and Coupled Processes Process Model Report. These activities were performed to investigate in situ flow and transport processes. The evaluations provide the necessary framework to: (1) refine and confirm the conceptual model of matrix and fracture processes in the unsaturated zone (UZ) and (2) analyze the impact of excavation (including use of construction water and effect of ventilation) on the UZ flow and transport processes. This AMR is intended to support revisions to ''Conceptual and Numerical Models for UZ Flow and Transport'' and ''Unsaturated Zone Flow and Transport Model Process Model Report''. In general, the results discussed in this AMR are from studies conducted using a combination or a subset of the following three approaches: (1) air-injection tests, (2) liquid-release tests, and (3) moisture monitoring using in-drift sensors or in-borehole sensors, to evaluate the impact of excavation, ventilation, and construction-water usage on the surrounding rocks. The liquid-release tests and air-injection tests provide an evaluation of in situ fracture flow and the competing processes of matrix imbibition. Only the findings from testing and data not covered in the ''Seepage Calibration Model and Seepage Testing Data'' are analyzed in detail in the AMR.
Date: December 14, 2001
Creator: Wang, J.
Partner: UNT Libraries Government Documents Department

The Optimum Plutonium Inert Matrix Fuel Form for Reactor-Based Plutonium Disposition

Description: The University of Florida has underway an ongoing research program to validate the economic, operational and performance benefits of developing an inert matrix fuel (IMF) for the disposition of the U.S. weapons plutonium (Pu) and for the recycle of reprocessed Pu. The current fuel form of choice for Pu disposition for the Department of Energy is as a mixed oxide (MOX) (PuO2/UO2). We will show analyses that demonstrate that a Silicon Carbide (SiC) IMF offers improved performance capabilities as a fuel form for Pu recycle and disposition. The reason that UF is reviewing various materials to serve as an inert matrix fuel is that an IMF fuel form can offer greatly reduced Pu and transuranic isotope (TRU) production and also improved thermal performance characteristics. Our studies showed that the Pu content is reduced by an order of magnitude while centerline fuel temperatures are reduced approximately 380 degrees centigrade compared to MOX. These reduced temperatures result in reduced stored heat and thermal stresses in the pellet. The reduced stored heat reduces the consequences of the loss of coolant accident, while the reduced temperatures and thermal stresses yield greatly improved fuel performance. Silicon Carbide is not new to the nuclear industry, being a basic fuel material in gas cooled reactors.
Date: October 6, 2004
Creator: Tulenko, J.S.; Wang, J. & Acosta, C.
Partner: UNT Libraries Government Documents Department

Environment Assessment, Resource Evaluation, and Underground Science in Southeastern California and Southwestern Nevada

Description: The geologically unique region of southeastern California and southwestern Nevada has both very high peaks and the lowest point, Death Valley, in the U.S. These features have significant effects on research in nuclear waste disposal, climate change, and evaluation of the potential for underground science in that region. These areas of scientific research can be further coordinated and expanded: (1) For nuclear waste, the studies of the Yucca Mountain site northeast of Death Valley contribute to the understanding of unsaturated and saturated flow and transport in an arid environment, with sensitivity to infiltration, under present-day and future climate conditions. (2) For climate research, water resources in hydrographic basins are being evaluated, in light of the prediction that there will be large decreases in snow accumulations (by 50%) in the 21st century. Further coupling of general circulation models with subsurface processes can increase understanding of hydrological responses to climate changes, with findings potentially applicable to other climate-stressed regions. (3) The combination of earth science testing and physics experimentation in underground laboratories signifies a promising research opportunity for the Death Valley region. Telescope Peak (along the western border of Death Valley), Boundary Peak (along the California-Nevada border), Mount Charleston (outside Las Vegas), and Mt. Tom (along the Pine Creek valley) are potential sites, with horizontal tunneling below peaks from valley floors to reach the depth required for low cosmic ray background. The use of existing mines in the region could also be explored for research in both earth science at different depths and the next generation of physics (e.g., neutrino mass measurements).
Date: May 12, 2004
Creator: Wang, J.
Partner: UNT Libraries Government Documents Department