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Acoustic radiation from two-dimensional rectangular cutouts in aerodynamic surfaces

Description: From Introduction: "The experiments in high-speed flow showed that an intense, high-frequency acoustic radiation is an essential feature of the problem. Consequently, a study of the acoustic field (involving schlieren observations and frequency and intensity measurements) was undertaken. This report presents the salient features of the study, which was mainly exploratory."
Date: August 1955
Creator: Krishnamurty, K
Partner: UNT Libraries Government Documents Department

Nb3Sn for Radio Frequency Cavities

Description: In this article, the suitability of Nb3Sn to improve theperformance of superconducting Radio-Frequency (RF)cavities is discussed.The use of Nb3Sn in RF cavitiesis recognized as an enabling technology toretain a veryhigh cavity quality factor (Q0) at 4.2 K and tosignificantly improve the cavity accelerating efficiency per unitlength(Eacc). This potential arises through the fundamental properties ofNb3Sn. The properties that are extensively characterized in theliterature are, however, mainly related to improvements in currentcarrying capacity (Jc) in the vortex state. Much less is available forthe Meissner state, which is of key importance to cavities. Relevantdata, available for the Meissner state is summarized, and it is shown howthis already validates the use of Nb3Sn. In addition, missing knowledgeis highlighted and suggestions are given for further Meissner statespecific research.
Date: December 18, 2006
Creator: Godeke, A.
Partner: UNT Libraries Government Documents Department


Description: CEBAF at JLab is in the process of an energy upgrade from 6 GeV to 12 GeV. The existing setup of the RF separator cavities in the 5th pass will not be adequate to extract the highest energy (11 GeV) beam to any two existing halls (A, B or C) while simultaneously delivering to the new hall D in the case of the proposed 12 GeV upgrade of the machine. To restore this capability, we are exploring the possibility of extension of existing normal conducting 499 MHz TEM-type rf separator cavities. Detailed numerical studies suggest that six 2-cell normal conducting structures meet the requirements; each 2-cell structure will require up to 4 kW RF input power in contrast with the current nominal operating power of 1.0 to 2.0 kW. A high power test of 4 kW confirms that the cavity meet the requirement.
Date: July 1, 2012
Creator: Ahmed, S.; Wissmann, M.; Mammosser, J.; Hovater, C.; Spata, M.; Krafft, G. et al.
Partner: UNT Libraries Government Documents Department


Description: Because the time of flight in a linear non-scaling FFAG depends on the transverse amplitude, motion in the longitudinal plane will be different for different transverse particle amplitudes. This effect, if not considered, will lead the failure of a substantial portion of the beam to be accelerated. I will first briefly review this effect. Then I will outline some techniques for addressing the problems created by the effect. In particular, I will discuss partially correcting the chromaticity and increasing the energy gain per cell. I will discuss potential problems with another technique, namely the introduction of higher harmonic cavities.
Date: November 6, 2006
Creator: Berg, J. S.
Partner: UNT Libraries Government Documents Department

Techniques for Identifying and Measuring High Order Modes in RF Cavities

Description: We report on a number of techniques which can be used to unravel the higher-order-mode spectrum of an RF cavity. Most of these techniques involve the application of basic symmetry principles and require for their application only that the cavity exhibit some basic symmetry, possibly broken by the presence of couplers, apertures, etc., which permits a classification of these modes in terms of some property characterized by that symmetry, e.g., multipolarity for a cavity which is basically a figure of revolution. Several examples of the application of these techniques are given.
Date: May 1, 1997
Creator: Goldberg, D.A. & Rimmer, R.A.
Partner: UNT Libraries Government Documents Department

High-Frequency Limit of Longitudinal Impedance

Description: A method of iterations which takes into account finite widths of resonances is developed and used to calculate the longitudinal impedance for a cylindrical cavity with side pipes. In the high-frequency limit the dependence of the real part of the impedance on the frequency is omega^(-1/2) in agreement with the estimate for the average impedance obtained by G. Do^me.
Date: August 1, 1987
Creator: Heifets, Sam & Heifets, Sam
Partner: UNT Libraries Government Documents Department

The Loss Parameters for Very Short Bunches

Description: Semi-empirical formulas for the transverse and longitudinal loss factors generated by cavity and step discontinuities are given in the limit of short bunch length.The parametric transition between the cavity and step approximations is considered.The differences between the impedances offered by periodic structures and isolated single cavities are also discussed.
Date: June 1, 1988
Creator: Yunn, Byung; Bisognano, Joseph & Heifets, Sam
Partner: UNT Libraries Government Documents Department

Semisolid Metal Processing Consortium

Description: Mathematical modeling and simulations of semisolid filling processes remains a critical issue in understanding and optimizing the process. Semisolid slurries are non-Newtonian materials that exhibit complex rheological behavior. There the way these slurries flow in cavities is very different from the way liquid in classical casting fills cavities. Actually filling in semisolid processing is often counter intuitive
Date: January 10, 2002
Creator: Apelian,Diran
Partner: UNT Libraries Government Documents Department

Synchro-betatron resonances in the 8 GeV proton driver

Description: The major difference of these two versions is the size (circumference) and the maximum energy. In the first study, the circumference is chosen to be 711.3m, which is 1.5 times the present Booster, with the maximum energy of 16 GeV. In the second version, it is mandated to be the same as Booster together with the same maximum energy of 8 GeV. One of the major impacts of the reduced size of the ring is the inevitable reduction in the total length of available space for injection/collimation/extraction systems and for rf cavities, 14 slots of 7.43m each in the smaller ring compared with 24 slots of 6.15m each in the larger ring. Since each cavity occupies a slot of 2.35m and 22 cavities are desirable, seven or eight slots out of 14 in the smaller ring must be reserved for rf, only six or seven remaining for all other systems. The constraint in space is particularly troublesome for the extraction system since the beam loss at extraction (at the highest beam energy) is the major concern of any high intensity proton machines.
Date: December 2, 2002
Creator: Ohnuma, Shoroku
Partner: UNT Libraries Government Documents Department

Final Report for "Compact Crab Cavity Design"

Description: The goal of this project is to provide an innovative, new crab cavity design relevant to the MEIC. Through this work, we will provide comprehensive modeling of this new cavity design, including electromagnetic, thermal, and microphonic effects. One most likely candidate configuration is the design put forward by JLab and Lancaster University, UK, researchers known as the four-rod configuration. In the Phase I, Tech-X Corporation researchers performed analysis and design optimization and iteration, utilizing their state-of-the art time-domain particle-in-cell software, on a 400 MHz design for the LHC by JLab and Lancaster University, UK, researchers known as the four-rod design.
Date: November 8, 2012
Creator: Smithe, David N
Partner: UNT Libraries Government Documents Department

Fast Ferroelectric L-Band Tuner for Superconducting Cavities

Description: Analysis and modeling is presented for a fast microwave tuner to operate at 700 MHz which incorporates ferroelectric elements whose dielectric permittivity can be rapidly altered by application of an external voltage. This tuner could be used to correct unavoidable fluctuations in the resonant frequency of superconducting cavities in accelerator structures, thereby greatly reducing the RF power needed to drive the cavities. A planar test version of the tuner has been tested at low levels of RF power, but at 1300 MHz to minimize the physical size of the test structure. This test version comprises one-third of the final version. The tests show performance in good agreement with simulations, but with losses in the ferroelectric elements that are too large for practical use, and with issues in bonding of ferroelectric elements to the metal walls of the tuner structure.
Date: March 1, 2011
Creator: Hirshfield, Jay L.
Partner: UNT Libraries Government Documents Department

Individual RF Test Results of the Cavities Used in the First US-built ILC-type Cryomodule

Description: Eight 1.3-GHz, nine-cell SRF cavities have been installed in a cryomodule intended to demonstrate the ILC design goal of 31.5 MV/m. These cavities all underwent two types of individual RF testing: a low-power continuous-wave test of the 'bare' cavity and a high-power pulsed test of the 'dressed' cavity. Presented here is a discussion of the results from these tests and a comparison of their performance in the two configurations.
Date: July 2012
Creator: Hocker, A; Harms, E R; Lunin, A; Sergatskov, D A; Sukhanov, A I; Eremeev, G V et al.
Partner: UNT Libraries Government Documents Department

Investigations on Absorber Materials at Cryogenic Temperatures

Description: In the framework of the 12 GeV upgrade project for the Continuous Electron Beam Accelerator Facility (CEBAF) improvements are being made to refurbish cryomodules housing Thomas Jefferson National Accelerator Facility’s (JLab) original 5-cell cavities. Recently we have started to look into a possible simplification of the existing Higher Order Mode (HOM) absorber design combined with the aim to find alternative material candidates. The absorbers are implemented in two HOM-waveguides immersed in the helium bath and operate at 2 K temperature. We have built a cryogenic setup to perform measurements on sample load materials to investigate their lossy characteristics and variations from room temperature down to 2 K. Initial results are presented in this paper.
Date: May 1, 2009
Creator: Frank Marhauser, Thomas Elliott, Robert Rimmer
Partner: UNT Libraries Government Documents Department

Design of Electron and Ion Crabbing Cavities for an Electron-Ion Collider

Description: Beyond the 12 GeV upgrade at the Jefferson Lab a Medium Energy Electron-Ion Collider (MEIC) has been considered. In order to achieve the desired high luminosities at the Interaction Points (IP), the use of crabbing cavities is under study. In this work, we will present to-date designs of superconducting cavities, considered for crabbing both ion and electron bunches. A discussion of properties such as peak surface fields and higher-order mode separation will be presented. Keywords: super conducting, deflecting cavity, crab cavity.
Date: July 1, 2012
Creator: Alejandro Castilla Loeza, Geoffrey Krafft, Jean Delayen
Partner: UNT Libraries Government Documents Department

Progress of ILC High Gradient SRF Cavity R&D at Jefferson Lab

Description: Latest progress of ILC high gradient SRF cavity R&D at Jefferson Lab will be presented. 9 out of 10 real 9-cell cavities reached an accelerating gradient of more than 38 MV/m at a unloaded quality factor of more than 8 {center_dot} 109. New understandings of quench limitation in 9-cell cavities are obtained through instrumented studies of cavities at cryogenic temperatures. Our data have shown that present limit reached in 9-cell cavities is predominantly due to localized defects, suggesting that the fundamental material limit of niobium is not yet reached in 9-cell cavities and further gradient improvement is still possible. Some examples of quench-causing defects will be given. Possible solutions to pushing toward the fundamental limit will be described.
Date: September 1, 2011
Creator: R.L. Geng, J. Dai, G.V. Eremeev, A.D. Palczewski
Partner: UNT Libraries Government Documents Department

SRF Cavity High-Gradient Study at 805 MHz for Proton and Other Applications

Description: 805 MHz elliptical SRF cavities have been used for SNS as the first application for protons. At LANL, an R&D started to explore a capability of getting high-gradient cavities (40-50 MV/m) at this frequency for the future applications such as proton and muon based interrogation testing facility added to the LANSCE accelerator and a power upgrade of the LANSCE accelerator for the fission and fusion material test station. Optimized cell designs for “standard”, “low-loss” and “re-entrant” shapes, cavity test results for “standard” single-cell cavities with temperature mapping as well as surface inspection results will be presented.
Date: May 1, 2009
Creator: Tajima, T; Chacon, P; Edwards, R L; Eremeev, G V; Krawczyk, F L; Roybal, R J et al.
Partner: UNT Libraries Government Documents Department


Description: CEBAF 12GeV upgrade project includes 80 new 7-cell cavities to form 10 cryomodules. Each cavity underwent RF qualification at 2.07K using a high power accelerating gradient test and an HOM survey in Jefferson Lab's Vertical Testing Area (VTA) before cavity string assembly. In order to ensure consistently high quality data, updated cavity testing procedures and analysis were implemented and used by a group of VTA operators. For high power tests, a cavity testing procedure was developed and used in conjunction with a LabVIEW program to collect the test data. Additionally while the cavity was at 2.07K, an HOM survey was performed using a network analyzer and a combination of Excel and Mathematica programs. Data analysis was standardized and an online logbook, Pansophy, was used for data storage and mining. The Pansophy system allowed test results to be easily summarized and searchable across all cavity tests. In this presentation, the CEBAF 12GeV upgrade cavity testing procedure, method for data analysis, and results reporting results will be discussed.
Date: July 1, 2012
Creator: Tiffany Bass, G. Davis, Christiana Wilson, Mircea Stirbet
Partner: UNT Libraries Government Documents Department

Recirculating Beam Breakup Study for the 12 GeV Upgrade at Jefferson Lab

Description: Two new high gradient C100 cryomodules with a total of 16 new cavities were installed at the end of the CEBAF south linac during the 2011 summer shutdown as part of the 12-GeV upgrade project at Jefferson Lab. We surveyed the higher order modes (HOMs) of these cavities in the Jefferson Lab cryomodule test facility and CEBAF tunnel. We then studied recirculating beam breakup (BBU) in November 2011 to evaluate CEBAF low energy performance, measure transport optics, and evaluate BBU thresholds due to these HOMs. This paper discusses the experiment setup, cavity measurements, machine setup, optics measurements, and lower bounds on BBU thresholds by new cryomodules.
Date: July 1, 2012
Creator: Ilkyoung Shin, Todd Satogata, Shahid Ahmed, Slawomir Bogacz, Mircea Stirbet, Haipeng Wang, Yan Wang, Byung Yunn, Ryan Bodenstein
Partner: UNT Libraries Government Documents Department