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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

Intracavity Frequency Doubling of a Diode-Pumped, External Cavity, Surface Emitting Semiconductor Laser

Description: The authors present a compact, robust, solid-state blue light (490 nm) source capable of greater than 5 mW of output in a TEM{sub 00} mode. This device is an optically pumped, vertical external-cavity surface-emitting laser (VECSEL) with an intracavity frequency doubling crystal.
Date: April 22, 1999
Creator: Alford, W.J.; Allerman, A.A.; Crawford, M.H. & Raymond, T.D.
Partner: UNT Libraries Government Documents Department

Toward a simple molecular understanding of sum frequency generation at air-water interfaces

Description: Second-order vibrational spectroscopies successfully isolate signals from interfaces, but they report on intermolecular structure in a complicated and indirect way. Here we adapt a perspective on vibrational response developed for bulk spectroscopies to explore the microscopic fluctuations to which sum frequency generation (SFG), a popular surface-specific measurement, is most sensitive. We focus exclusively on inhomogeneous broadening of spectral susceptibilities for OH stretching of HOD as a dilute solute in D{sub 2}O. Exploiting a simple connection between vibrational frequency shifts and an electric field variable, we identify several functions of molecular orientation whose averages govern SFG. The frequency-dependence of these quantities is well captured by a pair of averages, involving alignment of OH and OD bonds with the surface normal at corresponding values of the electric field. The approximate form we obtain for SFG susceptibility highlights a dramatic sensitivity to the way a simulated liquid slab is partitioned for calculating second-order response.
Date: January 13, 2009
Creator: Noah-Vanhoucke, Joyce; Smith, Jared D. & Geissler, Phillip L.
Partner: UNT Libraries Government Documents Department

Observations involving broadband impedance modelling

Description: Results for single- and multi-bunch instabilities can be significantly affected by the precise model that is used for the broadband impendance. This paper discusses three aspects of broadband impendance modeling. The first is an observation of the effect that a seemingly minor change in an impedance model has on the single-bunch mode coupling threshold. The second is a successful attempt to construct a model for the high-frequency tails of an r.f cavity. The last is a discussion of requirements for the mathematical form of an impendance which follow from the general properties of impendances.
Date: August 1, 1995
Creator: Berg, J. S.
Partner: UNT Libraries Government Documents Department

Observations of collective effects at the Advanced Light Source

Description: We present a summary of measurements of single beam collective effects in the Advanced Light Source (ALS). We describe measurements of coupled-bunch instabilities, including some recent results using the newly commissioned feedback systems and the results of an initial search for the fast ion instability. Single bunch effects include bunch lengthening, energy spread increase, HOM loss measurements, head-tail damping rates, current dependent tune shifts, and transverse mode coupling instability threshold. The longitudinal measurements are consistent with a broadband impedance {vert_bar}{Zeta}{sub {parallel}}/{eta}{vert_bar}{sub eff} = 0.22{plus_minus}0.07 {Omega} and transverse measurements indicate broadband impedances of {Zeta}{sub y,eff} = 155 k{Omega}/m and Z{sub x,eff} = 58 k{Omega}/m.
Date: October 1, 1995
Creator: Byrd, J.M.; Barry, W.; Corlett, J.N.; Fox, J. & Teytelman, D.
Partner: UNT Libraries Government Documents Department

Development and integration of applique decoupling capacitors

Description: For high-speed integrated circuit applications, it is important to interconnect decoupling capacitors and integrated circuits (ICs) as intimately as possible, to minimize parasitic impedances. This can be achieved by mounting free-standing, thin film capacitors directly onto ICs as part of a chip-scale packaging approach. These applique capacitors utilize a chemically-prepared PLZT dielectric, which is nominally 1 {micro}m thick. The small size and weight of applique capacitors can be used to improve packaging efficiency. Applique capacitors, which are initially fabricated on silicon wafers, have high permittivity ({var_epsilon} {approx_equal} 1,000), low loss (tan{delta} {approx_equal} 0.01) and high breakdown strength (E{sub b} {approx_equal} 1 MV/cm) and leakage resistance ({rho} > 10{sup 14} {Omega}-cm {at} 125 C). Various processes being developed to remove the capacitors from the silicon substrate and reattach them to ICs is described. In addition, a concept for interconnecting the capacitors using a repatterning process is discussed.
Date: October 1, 1996
Creator: Garino, T.J.; Dimos, D. & Lockwood, S.J.
Partner: UNT Libraries Government Documents Department

Force-limited vibration tests aplied to the FORTE` satellite

Description: A force limited random vibration test was conducted on a small satellite called FORTE{prime}. This type of vibration test reduces the over testing that can occur in a conventional vibration test. Two vibration specifications were used in the test: The conventional base acceleration specification, and an interface force specification. The vibration level of the shaker was controlled such that neither the table acceleration nor the force transmitted to the test item exceeded its specification. The effect of limiting the shake table vibration to the force specification was to reduce (or ``notch``) the shaker acceleration near some of the satellite`s resonance frequencies. This paper describes the force limited test conducted for the FORTE{prime} satellite. The satellite and its dynamic properties are discussed, and the concepts of force limiting theory are summarized. The hardware and setup of the test are then described, and the results of the force limited vibration test are discussed.
Date: February 1, 1996
Creator: Stevens, R.R. & Butler, T.A.
Partner: UNT Libraries Government Documents Department

Self-stressing structures for wafer-level oxide breakdown to 200 MHz

Description: We have demonstrated for the first time high frequency (210 MHz) oxide breakdown at the wafer-level using on-chip, self-stressing test structures. This is the highest frequency oxide breakdown that has been reported. We used these structures to characterize the variation in oxide breakdown with frequency (from 1 Hz to over 200 MHz) and duty cycle (from 10% to 90%). Since the stress frequency, duty cycle and temperature are controlled by DC signals in these structures, we used conventional DC wafer-level equipment without any special modifications (such as high frequency cabling). This self-stressing structure significantly reduces the cost of performing realistic high frequency oxide breakdown experiments necessary for developing reliability models and building-in-reliability.
Date: February 1, 1995
Creator: Snyder, E.S.; Tanner, D.M.; Bowles, M.R.; Swanson, S.E.; Anderson, C.H. & Perry, J.P.
Partner: UNT Libraries Government Documents Department

Localized wave pulses in the keyport experiment

Description: Localized wave (LW) pulses were produced using a standard Navy array in the anechoic tank at Navy Underwater Weapons Center (NUWC) Keyport. The LW pulses used were the MPS pulse first derived by Ziolkowski, and a new type of pulse based on a superposition of Gaussian beam modes. This new type is motivated by a desire to make a comparison of the MPS pulse with another broad band pulse built from solutions to the wave equation. The superposed Gaussian pulse can be described by parameters which are analogous to those describing the MPS pulse. We compare the directivity patternsand the axial energy decay between the pulses. We find the behavior of the pulses to be similar so that the superposed Gaussian could be another candidate in the class of low diffractive pulses known as localized waves.
Date: February 17, 1998
Creator: Chambers, D.H. & Lewis, D.K.
Partner: UNT Libraries Government Documents Department

Characterization and equalization of the AC responses of the corrector magnets for the APS local orbit feedback system

Description: Local feedback for the APS storage ring uses local bumps to control the position and angle of the positron beam through each x-ray source point. Induced eddy currents in the aluminum vacuum chamber dominate the AC characteristics of the corrector magnetic fields. Small differences in the geometries at each magnet location change the eddy current effects and result in bump closure errors which must be reduced in order to minimize the coupling between each of the many local loops and the global control loop. By a combination of flux-damping coils, flux-shielding copper sheets, and a set of steel laminations for end-flux clamping, the differences of the eddy current effects between two corrector magnets were reduced from 0.18 Gm/A to 0.035 Gm/A in the frequency span of 0.1-100 Hz.
Date: August 1, 1997
Creator: Doose, C. & Kim, S.H.
Partner: UNT Libraries Government Documents Department

Analysis and application of microwave radiation from the damping manifolds of the SLAC Damped Detuned Structures (DDS)

Description: The power spectrum emerging from the damping manifolds of a DDS provides valuable quasi-local information on the displacement of a drive beam from the axis of individual cells, where the displacement may be due to beam offset, small cell misalignment, or a combination of the two. The degree of localization and the indexing of frequency to cell number is determined directly from the spectral function theory. Examples for specific DDS designs will be presented. These relations can be used to determine geometrical misalignment patterns.
Date: May 1, 1997
Creator: Jones, R.M.; Seidel, M. & Miller, R.H.
Partner: UNT Libraries Government Documents Department

Tune modulation due to synchrotron oscillations and chromaticity, and the dynamic aperture

Description: A tracking study was done of the effects of a tune modulations, due to synchrotron oscillations and the tune dependence on momentum (chromaticity), on the dynamic aperture. The studies were done using several RHIC lattices and tracking runs of about 1 {times} 10{sup 6} turns. The dynamic aperture was found to decrease roughly linearly with the amplitude of the tune modulation. Lower order non-linear resonances, like the 1/3 and 1/4 resonance are not crossed because of the tune modulation. Three different cases were studied, corresponding to RHIC lattices with different {beta}*, and with different synchrotron oscillation amplitudes. In each case, the tune modulation amplitude was varied by changing the chromaticity. In each case, roughly the same result, was found. The result found here for the effect of a tune modulation due to chromaticity may be compared with the result found for the effect of a tune modulation due to a gradient ripple in the quadrupoles. The effect of a tune modulation due to a gradient ripple appears to be about 4 times stronger than the effect of a tune modulation due to chromaticity and synchrotron oscillations.
Date: May 1, 1995
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Localized wave generation with a standard underwater array

Description: Recent work at the Navy Underwater Weapons Center Keyport test facility showed that existing Navy field equipment could generate Localized Waves. Results of angular scans show a narrowed beam pattern and lowered side lobes relative to standard beams. Results of axial range scans show evidence or an extended near field. Frequency analysis shows that the main beam is a decade wide while the surviving grating lobes are narrow band width, high frequency.
Date: February 17, 1998
Creator: Lewis, D.K.; Chambers, D.H.; Mullin, C.S. & Ziolkowski, R.W.
Partner: UNT Libraries Government Documents Department


Description: The frequency dependence of the longitudinal beam transfer function (BTF) in a storage ring, when expressed in a basis of azimuthal harmonics of the line density, is the Fourier transform of a causal function that depends on the radio-frequency potential well in which the bunch moves. The effect of all synchrotron harmonics are included in this function, which is derived from Krinsky and Wang's expression for the BTF expressed in the same basis (S. Krinsky and J.-M. Wang, Part. Accel. 17, 109-139 (1985)). Analytic properties of the terms of the BTF expressed in a series of synchrotron harmonics, which are approximately Shaposhnikova's BTF matrix elements (E. Shaposhnikova, CERN Report No. SL-94-19-RF (1994)), are studied through the large-argument asymptotics of corresponding causal functions.
Date: June 18, 2001
Creator: TOWNE, N.
Partner: UNT Libraries Government Documents Department

The Synthesis of Structural Responses Using Experimentally Measured Frequency Response Functions and Field Test Data

Description: This paper presents an analysis technique used to generate the structural response at locations not measured during the ejection of a captive-carried store. The ejection shock event is complicated by the fact that forces may be imparted to the store at eight distinct locations. The technique derives forcing functions by combining the initial field test data for a limited number of measurement locations with Frequency Response Functions (FRFs) measured using a traditional modal-type impact (tap) test at the same locations. The derived forcing functions were then used with tap test FRFs measured at additional locations of interest to produce the desired response data.
Date: November 17, 2000
Partner: UNT Libraries Government Documents Department


Description: Using a single particle dynamics approach: the major magnetic non-linearities of the SNS accumulator ring are studied. Frequency maps are employed in order to display the global dynamics of the beam, for several working points. By means of diffusion maps the major resonances are explored and their bandwidth is estimated. The global tune diffusion coefficient is finally used to compare and choose the best working point.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department


Description: The chromatic nonlinearity parameter, {alpha}{sub 1}, has a strong impact on longitudinal dynamics in the vicinity of transition [1,2,3]. Measurements of the synchrotron frequency as a function of radius are used to constrain the value of {alpha}{sub 1}.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Force Reduction Factors for the Structural Design and Evaluation of Facilities Containing Nuclear and Hazardous Materials

Description: This report examines significant contributions to inelastic behavior of common building systems and develops frequency dependent force reduction factors that may be used with the results from linear elastic analyses models.
Date: July 26, 2001
Creator: Mertz, G.E.
Partner: UNT Libraries Government Documents Department

Calculation of the coupling impedances of holes and slots on the liner using MAFIA and scaling

Description: The location of a liner inside the beam tube is one of the options considered for the Super Colliders. The liner could serve as a synchrotron radiation intercept and also help enhance the vacuum. A definite distribution of holes or slots is required to be located on the liner for pumping out the desorbing gases. There will be wake fields propagating within the liner due to diffraction at discontinuities following the incident beam fields. The effect of these wake fields can be minimized by adopting the least number of pumping holes/slots required and through an optimal choice of hole/slot shape and size. The effect of the wake fields on the beam may be expressed through coupling impedances defined proportional to the corresponding forces integrated through distance per unit charge. It is necessary to compute the impedance of holes and slots and determine the scaling of the impedance with the dimensions of the hole/slot and the liner, in order to optimize the choice of pumping holes/slots. The coupling impedances of slots and holes have been calculated here using the code MAFIA and the scaling assessed. The results compare favorably with existing analytical results.
Date: November 1, 1993
Creator: Thiagarajan, V.; Barts, T.; Kurennoy, S. & Chou, W.
Partner: UNT Libraries Government Documents Department

Application of frequency map analysis to the ALS

Description: Frequency map analysis is a numerical method based on Fourier techniques which provides a clear representation of the global dynamics of many multi-dimensional systems, and which is particularly useful for systems of 3 degrees of freedom and more. The frequency dependence with time also allows refined estimates of the diffusion of the orbits. Here are presented the theoretical foundation of the method, and some applications to the Advanced Light Source, demonstrating how frequency map analysis can be used to understand the limits of the dynamic aperture under various lattice conditions and predict more favorable working points.
Date: January 1, 1996
Creator: Laskar, J. & Robin, D.
Partner: UNT Libraries Government Documents Department

Dynamic modulus estimation and structural vibration analysis.

Description: Often the dynamic elastic modulus of a material with frequency dependent properties is difficult to estimate. These uncertainties are compounded in any structural vibration analysis using the material properties. Here, different experimental techniques are used to estimate the properties of a particular elastomeric material over a broad frequency range. Once the properties are determined, various structures incorporating the elastomer are analyzed by an interactive finite element method to determine natural frequencies and mode shapes. Then, the finite element results are correlated with results obtained by experimental modal analysis.
Date: November 18, 1998
Creator: Gupta, A.
Partner: UNT Libraries Government Documents Department

High frequency breakdown voltage

Description: This report contains information about the effect of frequency on the breakdown voltage of an air gap at standard pressure and temperature, 76 mm Hg and O{degrees}C, respectively. The frequencies of interest are 47 MHz and 60 MHz. Additionally, the breakdown in vacuum is briefly considered. The breakdown mechanism is explained on the basis of collision and ionization. The presence of the positive ions produced by ionization enhances the field in the gap, and thus determines the breakdown. When a low-frequency voltage is applied across the gap, the breakdown mechanism is the same as that caused by the DC or static voltage. However, when the frequency exceeds the first critical value f{sub c}, the positive ions are trapped in the gap, increasing the field considerably. This makes the breakdown occur earlier; in other words, the breakdown voltage is lowered. As the frequency increases two decades or more, the second critical frequency, f{sub ce}, is reached. This time the electrons start being trapped in the gap. Those electrons that travel multiple times across the gap before reaching the positive electrode result in an enormous number of electrons and positive ions being present in the gap. The result is a further decrease of the breakdown voltage. However, increasing the frequency does not decrease the breakdown voltage correspondingly. In fact, the associated breakdown field intensity is almost constant (about 29 kV/cm).The reason is that the recombination rate increases and counterbalances the production rate, thus reducing the effect of the positive ions` concentration in the gap. The theory of collision and ionization does not apply to the breakdown in vacuum. It seems that the breakdown in vacuum is primarily determined by the irregularities on the surfaces of the electrodes. Therefore, the effect of frequency on the breakdown, if any, is of secondary importance.
Date: March 1, 1992
Creator: Chu, Thanh Duy
Partner: UNT Libraries Government Documents Department