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Study of the emission performance of high-power klystrons: SLAC XK-5

Description: There are hundreds of high power klystrons operated in the Linac gallery and about fifty to sixty tubes fail every year. The lifetime ranges from a few thousand up to seventy thousand hours except those which fail during an early period. The overall percentage of failures due to emission problems is approximately 25%. It is also noted that a 10% increase in mean lifetime of klystrons will reduce the overall cost per hour as much as a 10% increase in efficiency. Therefore, it is useful to find some method to predict the expected life of an individual tube. The final goal has not been attained yet, but some useful information was obtained. It is thought that this information might be helpful for those people who will study this subject further.
Date: July 1, 1981
Creator: Zhao, Y.
Partner: UNT Libraries Government Documents Department

The waveform analysis for Zarem type high voltage pulse generator

Description: The project of the cluster klystron requires a 30 to 40 kV pulse generator to drive the mod-anode. A 30--40 kV pulse generator using Zarem type was developed. A pulse distortion showing a deficiency on the rear top was frequently encountered. This note describes the detail of the pulse forming principle. The encountered distortion was analyzed. Simulations demonstrate the same result. The feature of the spark gap was also addressed. A solution of this problem is given.
Date: October 1, 1995
Creator: Zhao, Y.
Partner: UNT Libraries Government Documents Department


Description: This note addresses the general concerns for the design of a ferrite cavity. The parameters are specified for the RCMS, for which the frequency ramp is in the range of 1.27 MHz to 6.44 MHz, or a ratio of 1:5.
Date: April 19, 2002
Creator: ZHAO, Y.
Partner: UNT Libraries Government Documents Department

A new structure of linear collider

Description: A new scheme is proposed for the muon collider cooling RF, on which the cavity is almost a simple pillbox. The principle is to divide the accelerating cells into three separate channels with a phase difference of 2{pi}/3 between each other. A special structure is designed in which each channel is like a side-coupled cavity structure operating at {pi}/2-mode, but an extra phase shift of {pi} is introduced so that the phase difference between two cells is 2{pi}. Therefore, the beam sees a 2{pi}/3-mode implying a high interaction between cavities and beam, while the RF system sees a {pi}/2-mode implying a high stability. In other words, it combines the advantages of both traveling wave and standing wave. The mechanical structure is also simple and compact because the side-coupled cavity is formed by a uniform rectangular-like waveguide, which is simply an arc section attached on the main cavities. The principle and the preliminary simulation are addressed in detail. This principle is also applicable for a 2{pi}/4 mode and other machine provided the coupling due to aperture is weak enough.
Date: July 1, 1998
Creator: Zhao, Y.
Partner: UNT Libraries Government Documents Department


Description: The Muon Collider and Neutrino Factory projects require low frequency rf cavities because the size and emittance of the muon beam is much larger than is usual for electron or proton beams. The range of 30 MHz to 200 MHz is of special interest. However, the size of an accelerator with low frequency will be impractically large if it is simply scaled up from usual designs. In addition, to get very high peak power in this range is difficult. Presented in this paper is an alternative structure that employs a quasi-lumped inductance that can significantly reduce the transverse size while keeping high gradient. Also addressed is a power compression scheme with a thyratron. This gives a possible solution to provide very high peak power.
Date: June 18, 2001
Creator: ZHAO, Y.
Partner: UNT Libraries Government Documents Department


Description: An FFAG moot likely requires rapid cavity tuning. The cavity must also have a very high gradient. To satisfy both the high power and rapid tuning requirements is a big challenge. Detailed investigation of the possibility is addressed. Included are general thoughts, dual-loop and simple loop analyses, and a study of using ferrite or PIN diodes. Also proposed is a phase control scheme, which may be a better solution if the needed components can be developed. Finally, an energy analysis reveals the difficult of high power tuning.
Date: July 12, 2001
Creator: ZHAO, Y.
Partner: UNT Libraries Government Documents Department


Description: It was found that the measured Q value of a tape resonator has a large difference with that calculated with MAFIA. This difference is recognized to be mainly due to the error in the simulation, which is unable to handle a sharp edge. This note addresses the 2-dimensional MAFIA simulation and conformal mapping. It shows the error could be as high as 60 %. Reasonable caution should be exercised in the use of MAFIA, and other codes as well, in calculating Q value if a sharp edge exists in the problem.
Date: October 1, 1999
Creator: ZHAO,Y.
Partner: UNT Libraries Government Documents Department

The pulse modulator for the mod-anode of the cluster klystron

Description: A high voltage pulse generator using a Zarem type modulator was developed. The Zarem type circuit doesn`t require a matched load, making it suitable to drive the mod-anode of the cluster klystron, which has a capacitive load. The principle and the experiments, as well as the analyses and the simulations of the observed phenomena, (ringing, pulse {open_quotes}skirt{close_quotes} and {open_quotes}deficiency{close_quotes}) are presented.
Date: May 1, 1996
Creator: Zhao, Y.; Palmer, R. & Wang, H.
Partner: UNT Libraries Government Documents Department


Description: This note addresses the various options for the Rapid Cycling Medical Synchrotron (RCMS) RF. The study was divided into three cases, namely non-tuning, tuning and filter. Each case also includes a few options. The primary study was focused on the non-tuning options. However, it was found that it requires too much driver power to cover the wide band and thus causes the cost being too high to be competitive. The proposal of RCMS is not yet clear if it can be approved or not. The results of this study might be useful to other similar machines.
Date: January 22, 2003
Creator: ZHAO,Y.
Partner: UNT Libraries Government Documents Department


Description: A superconducting cavity used in a microwave gun requires that the launcher and the pickup probes be on the same side of the cavity, which causes direct coupling between them, or crosstalk. At room temperature, the crosstalk causes serious distortion of the RF response. This note addresses the phenomenon, the simulation results and the analysis, so that one can extract the desired information from the confusing signal.
Date: October 21, 2002
Creator: ZHAO, Y.
Partner: UNT Libraries Government Documents Department

Parameterizing loop fusion for automated empirical tuning

Description: Traditional compilers are limited in their ability to optimize applications for different architectures because statically modeling the effect of specific optimizations on different hardware implementations is difficult. Recent research has been addressing this issue through the use of empirical tuning, which uses trial executions to determine the optimization parameters that are most effective on a particular hardware platform. In this paper, we investigate empirical tuning of loop fusion, an important transformation for optimizing a significant class of real-world applications. In spite of its usefulness, fusion has attracted little attention from previous empirical tuning research, partially because it is much harder to configure than transformations like loop blocking and unrolling. This paper presents novel compiler techniques that extend conventional fusion algorithms to parameterize their output when optimizing a computation, thus allowing the compiler to formulate the entire configuration space for loop fusion using a sequence of integer parameters. The compiler can then employ an external empirical search engine to find the optimal operating point within the space of legal fusion configurations and generate the final optimized code using a simple code transformation system. We have implemented our approach within our compiler infrastructure and conducted preliminary experiments using a simple empirical search strategy. Our results convey new insights on the interaction of loop fusion with limited hardware resources, such as available registers, while confirming conventional wisdom about the effectiveness of loop fusion in improving application performance.
Date: December 15, 2005
Creator: Zhao, Y; Yi, Q; Kennedy, K; Quinlan, D & Vuduc, R
Partner: UNT Libraries Government Documents Department

Microchannel Heat Exchangers with Carbon Dioxide

Description: The objective of the present study was to determine the performance of CO{sub 2} microchannel evaporators and gas coolers in operational conditions representing those of residential heat pumps. A set of breadboard prototype microchannel evaporators and gas coolers was developed and tested. The refrigerant in the heat exchangers followed a counter cross-flow path with respect to the airflow direction. The test conditions corresponded to the typical operating conditions of residential heat pumps. In addition, a second set of commercial microchannel evaporators and gas coolers was tested for a less comprehensive range of operating conditions. The test results were reduced and a comprehensive data analysis, including comparison with the previous studies in this field, was performed. Capacity and pressure drop of the evaporator and gas cooler for the range of parameters studied were analyzed and are documented in this report. A gas cooler performance prediction model based on non-dimensional parameters was also developed and results are discussed as well. In addition, in the present study, experiments were conducted to evaluate capacities and pressure drops for sub-critical CO{sub 2} flow boiling and transcritical CO{sub 2} gas cooling in microchannel heat exchangers. An extensive review of the literature failed to indicate any previous systematic study in this area, suggesting a lack of fundamental understanding of the phenomena and a lack of comprehensive data that would quantify the performance potential of CO{sub 2} microchannel heat exchangers for the application at hand. All experimental tests were successfully conducted with an energy balance within {+-}3%. The only exceptions to this were experiments at very low saturation temperatures (-23 C), where energy balances were as high as 10%. In the case of evaporators, it was found that a lower saturation temperature (especially when moisture condensation occurs) improves the overall heat transfer coefficient significantly. However, under such conditions, ...
Date: September 15, 2001
Creator: Zhao, Y.; Ohadi, M.M. & Radermacher, R.
Partner: UNT Libraries Government Documents Department

Minerals of the earth's deep interior

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project addresses the major geophysical issue of the nature of the seismic velocity and density discontinuity at 670 km depth (the boundary between upper and lower mantle with temperature about 1,900 K and pressure about 23 GPa). A phase change at this depth would represent a relatively small barrier to mantle convection through the discontinuity, but compositional change would inhibit thermal convection throughout the mantle. To address this problem the authors measured equation of state parameters in mantle minerals as functions of high P-T using single crystal x-ray diffraction with a unique, new diamond-anvil cell (DAC) at simultaneous high temperature and pressure. Single-crystal diffraction improves absolute accuracy in lattice constants over those from powder diffraction by a factor of 5 to 10. The authors have measured equations of state of orthoenstatite MgSiO{sub 3} and hexagonal boron nitride hBN.
Date: November 1, 1998
Creator: Schiferl, D.; Zhao, Y. & Shankland, T.J.
Partner: UNT Libraries Government Documents Department

Experiment of electrical conductivity at low temperature (preliminary measurement)

Description: A muon collider needs very large amount of RF power, how to reduce the RF power consumption is of major concern. Thus the application of liquid nitrogen cooling has been proposed. However, it is known that the electrical conductivity depends on many factors and the data from different sources vary in a wide range, especially the data of conductivity of beryllium has no demonstration in a real application. Therefore it is important to know the conductivity of materials, which are commercially available, and at a specified frequency. Here, the results of the preliminary measurement on the electrical conductivity of copper at liquid nitrogen temperature are summarized. Addressed also are the data fitting method and the linear expansion of copper.
Date: July 1, 1998
Creator: Zhao, Y. & Wang, H.
Partner: UNT Libraries Government Documents Department


Description: The electrical conductivity of beryllium at radio frequency (800 MHz) and liquid nitrogen temperature were investigated and measured. This summary addresses a collection of beryllium properties in the literature, an analysis of the anomalous skin effect, the test model, the experimental setup and improvements, MAFIA simulations, the measurement results and data analyses. The final results show that the conductivity of beryllium is not as good as indicated by the handbook, yet very close to copper at liquid nitrogen temperature.
Date: March 31, 2000
Creator: ZHAO,Y. & WANG,H.
Partner: UNT Libraries Government Documents Department

Stability and Electronic Structures of CuxS Solar Cell Absorbers: Preprint

Description: Cu{sub x}S is one of the most promising solar cell absorber materials that has the potential to replace the leading thin-film solar cell material Cu(In,Ga)Se{sub 2} for high efficiency and low cost. In the past, solar cells based on Cu{sub x}S have reached efficiency as high as 10%, but it also suffers serious stability issues. To further improve its efficiency and especially the stability, it is important to understand the stability and electronic structure of Cu{sub x}S. However, due to the complexity of their crystal structures, no systematic theoretical studies have been carried out to understand the stability and electronic structure of the Cu{sub x}S systems. In this work, using first-principles method, we have systematically studied the crystal and electronic band structures of Cu{sub x}S (1.25 < x {le} 2). For Cu{sub 2}S, we find that all the three chalcocite phases, i.e., the low-chalcocite, the high-chalcocite, and the cubic-chalcocite phases, have direct bandgaps around 1.3-1.5 eV, with the low-chalcocite being the most stable one. However, Cu vacancies can form spontaneously in these compounds, causing instability of Cu{sub 2}S. We find that under Cu-rich condition, the anilite Cu{sub 1.75}S is the most stable structure. It has a predicted bandgap of 1.4 eV and could be a promising solar cell absorber.
Date: July 1, 2012
Creator: Wei, S. H.; Xu, Q.; Huang, B.; Zhao, Y.; Yan, Y. & Noufi, R.
Partner: UNT Libraries Government Documents Department

Solenoid fringe field compensation for the Cluster Klystron

Description: Optimization of the solenoid pancake currents so as to have a uniform axial magnetic field over an extended volume, is very important for the successful operation of the Cluster Klystron. By boosting the first and the last pancake currents by 35%, a uniform field Br/Bz {le} 0.1% at radius R {le} 2 cm can be extended from {+-} 7 cm to {+-} 16 cm. The result confirms simulations and the requirements for a 3-beam Cluster Klystron Experiment are achieved.
Date: April 1, 1996
Creator: Wang, H.; Fernow, R.C.; Kirk, H.G.; Palmer, R.B. & Zhao, Y.
Partner: UNT Libraries Government Documents Department

Requirements of a proton beam accelerator for an accelerator-driven reactor

Description: When the authors first proposed an accelerator-driven reactor, the concept was opposed by physicists who had earlier used the accelerator for their physics experiments. This opposition arose because they had nuisance experiences in that the accelerator was not reliable, and very often disrupted their work as the accelerator shut down due to electric tripping. This paper discusses the requirements for the proton beam accelerator. It addresses how to solve the tripping problem and how to shape the proton beam.
Date: December 31, 1997
Creator: Takahashi, H.; Zhao, Y.; Tsoupas, N.; An, Y. & Yamazaki, Y.
Partner: UNT Libraries Government Documents Department

Development of a 10-bit 500 Msample/sec Waveform Digitizcr

Description: The device reported is a simple, robust, low-cost device to sample fast analog signals and convert them into digital data. Goal is to utilize existingleCroy Front End developments and BNL previous efforts to: Extend the dynamic range from 8 to 9-10 bits; Extend the depth of memory; Lower the cost; and Increase availability to general research and industrial cornmunity.
Date: September 25, 1996
Creator: Atiya, M; Padrazo, D; Zhao, Y; Sumner, R; Untermeyer, U; Carlson, B et al.
Partner: UNT Libraries Government Documents Department

A role of accelerator-driven reactor to meet future energy demands

Description: Fissile fuel can be produced at a high rate using an accelerator driven Pu fueled fast reactor operated at deep subcriticality; this approach avoids encountering a shortage of Pu during a high rate of growth in the production of nuclear energy. Slightly reducing the acceleration field minimizes the tripping of the beam and the radiation dose from the accelerator; hence the accelerator can be operated as a highly reliable industrial machine. The usefulness of a windowless liquid jet target, which eliminates the spreading of the beam and problems of radiation damage is emphasized, in association with the small size of the target. The requirements for a proton beam accelerator for this system are discussed.
Date: March 1, 1998
Creator: Takahashi, H.; An, Y.; Yang, Y.; Zhao, Y. & Tsoupas, N.
Partner: UNT Libraries Government Documents Department

A normal conducting accelerator for a muon collider demonstration machine

Description: The authors present a 250 GeV linac arrangement using normal conducting cavities that could be used for a muon collider demonstration machine. One scenario consists of six 200 MHz linacs and rapid cycling pulsed magnets to be installed in a tunnel with six straight sections. The RF parameters of the cavities are given. Another scenario consists of 800 MHz. Also addressed is the possibility of using normal conducting cavities with liquid nitrogen cooling, which has several advantages.
Date: May 1, 1997
Creator: Zhao, Y.; Palmer, R.; Fernow, R.; Gallardo, J. & Kirk, H.
Partner: UNT Libraries Government Documents Department