1,016 Matching Results

Search Results

Advanced search parameters have been applied.

Chromaticity measurement via the fourier spectrum of transverse oscillations

Description: Turn-by-turn data from a single BPM includes information on the chromaticity in sidebands displaced above and below the betatron frequency by an amount of the synchrotron frequency. It may be necessary to induce small amplitude synchrotron oscillation by giving the beam a small kick. Power spectrum of the BPM data gives clear chromatic sidebands, and they can be applied to the chromaticity measurement in the Fermilab Booster.
Date: August 13, 2004
Creator: Yang, Xi
Partner: UNT Libraries Government Documents Department

ON THE DENSITY OSCILLATIONS OF A WARM PARTICLE BUNCH

Description: The density oscillations of warm particle bunches is investigated theoretically. Two different mathematical approaches are employed to derive the basic equation describing density oscillations; one is a fluid approach and the second is a more general Green1s function formulation. The motion is analyzed in first order perturbation theory where it is shown, under the assumption of no degeneracy, that there are only stable oscillations. Second order perturbation theory gives damping of the motion. The perturbation theory is examined and a criterion is exhibited for its proper use. Thus, when the resistivity is small enough (but nonzero) then the motion is stable, but when the resistivity is large then the motion is essentially unstable with a growth rate which is that of an unbunched beam. The criterion is approximately evaluated using a model for a bunched beam.
Date: November 1, 1982
Creator: Channell, P.J.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Magnetomorphic Oscillations in Zinc

Description: In making this study it is important to search for ways to enhance and, if possible, make detection of MMO signals simpler in order that this technique for obtaining FS measurements may be extended to other materials. This attempt to improve measurement techniques has resulted in a significant discovery: the eddy-current techniques described in detail in a later section which should allow MMO to be observed and sensitively measured in many additional solids. The second major thrust of the study has been to use the newly discovered eddy-current technique in obtaining the first indisputable observation of MMO in zinc.
Date: August 1970
Creator: Waller, William Marvin
Partner: UNT Libraries

Motion-Dependent Fluid Forces Acting on a Tube Row in Crossflow

Description: Motion-dependent fluid forces acting on a tube row with a pitch-to-diameter ratio of 1.35 are measured for several flow velocities and a series of oscillation frequencies. Fluid-damping and fluid-stiffness coefficients are obtained from motion-dependent fluid forces as a function of reduced flow velocity. Fluid-force coefficients agree reasonably with published data. Based on the fluid-force coefficients, the critical flow velocity and instability characteristics of tube arrays in crossflow can be predicted.
Date: October 1986
Creator: Jendrzejczyk, J. A. & Chen, Shoei-Sheng
Partner: UNT Libraries Government Documents Department

MSW Effects in Vacuum Oscillations

Description: We point out that for solar neutrino oscillations with the mass-squared difference of Delta m^2 ~;; 10^-10 - 10^-9 eV^2, traditionally known as"vacuum oscillation'' range, the solar matter effects are non-negligible, particularly for the low energy pp neutrinos. One consequence of this is that the values of the mixing angle theta and pi/2-theta are not equivalent, leading to the need to consider the entire physical range of the mixing angle 0<=theta<=pi/2 when determining the allowed values of the neutrino oscillation parameters.
Date: February 6, 2000
Creator: Friedland, Alexander
Partner: UNT Libraries Government Documents Department

Performance of exponential coupler in the SPS with LHC type beam for transverse broadband instability analysis

Description: We present the performance and limitations of the SPS exponential coupler [1] for transverse instability measurements with LHC type beam. Data were acquired in 2008 in the SPS in the time domain with a bandwidth of up to 2.5 GHz. The data were filtered to extract the time evolution of transverse oscillations within the less than 5 ns long LHC type bunches. We describe the data filtering techniques and show the limitations of the pick-up due to propagating modes.
Date: May 25, 2009
Creator: de Maria,R.; Fox, J. D.; Hofle, W.; Kotzian, G.; Rumolo, G.; Salvant, B. et al.
Partner: UNT Libraries Government Documents Department

Enhanced Constraints on theta13 from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND

Description: We present new constraints on the neutrino oscillation parameters {Delta}m{sub 21}{sup 2}, {theta}{sub 12}, and {theta}{sub 13} from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of 3.49 x 10{sup 32} target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis ({theta}{sub 13} = 0) of the KamLAND and solar data yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.444{sub -0.030}{sup +0.036} and {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5} eV{sup 2}; a three-flavor analysis with {theta}{sub 13} as a free parameter yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.452{sub -0.033}{sup +0.035}, {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5}eV{sup 2}, and sin{sup 2} {theta}{sub 13} = 0.020{sub -0.016}{sup +0.016}. This {theta}{sub 13} interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global {theta}{sub 13} analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates sin{sup 2} {theta}{sub 13} = 0.017{sub -0.009}{sup +0.010}, a nonzero value at the 93% C.L. This finding will be further tested by upcoming accelerator and reactor experiments.
Date: September 24, 2010
Creator: Collaboration, The KamLAND; Gando, A.; Gando, Y.; Ichimura, K.; Ikeda, H.; Inoue, K. et al.
Partner: UNT Libraries Government Documents Department

On Nonlinear Self-interaction of Geodesic Acoustic Mode Driven by Energetic Particles

Description: It is shown that nonlinear self-interaction of energetic particle-driven Geodesic Acoustic Mode does not generate a second harmonic in radial electric field using the fluid model. However, kinetic effects of energetic particles can induce a second harmonic in the radial electric field. A formula for the second order plasma density perturbation is derived. It is shown that a second harmonic of plasma density perturbation is generated by the convective nonlinearity of both thermal plasma and energetic particles. Near the midplane of a tokamak, the second order plasma density perturbation (the sum of second harmonic and zero frequency sideband) is negative on the low field side with its size comparable to the main harmonic at low uctuation level. These analytic predictions are consistent with the recent experimental observation in DIII-D.
Date: June 4, 2010
Creator: Fu, G. Y.
Partner: UNT Libraries Government Documents Department

Some Notes on Wideband Feedback Amplifiers

Description: The extension of the passband of wideband amplifiers is a highly important problem to the designer of electronic circuits. Throughout the electronics industry and in many research programs in physics and allied fields where extensive use is made of video amplifiers, the foremost requirement is a passband of maximum width. This is necessary if it is desired to achieve a more faithful reproduction of transient wave forms, a btter time resolution in physical measurements, or perhaps just a wider band gain-frequency response to sine wave signals. The art of electronics is continually faced with this omnipresent amplifier problem. In particular, the instrumentation techniques of nuclear physics require amplifiers with short rise times, a high degree of gain stability, and a linear response to high signal levels. While the distributed amplifier{sup 1} may solve the problems of those seeking only a wide passband, the requirements of stability and linearity necessitate using feedback circuits. This paper considers feedback amplifiers from the standpoint of high-frequency performance. The circuit conditions for optimum steady-state (sinusoidal) and transient response are derived and practical circuits (both interstage and output) are presented which fulfill these conditions. In general, the results obtained may be applied to the low-frequency end. The fundamental limitation in feedback amplifiers arises from the over-all phase shift in the amplifier and in some cases, the feedback circuit as well. As the shift in phase approaches 180 degrees on either side of the mid-band, the feedback becomes positive, resulting in regeneration and possible oscillation. The relationships between attenuation and phase shift necessary for amplifier stability have been formulated and published{sup 2}. It is the phase shift and its attendant difficulties that make feeback over more than three stages impractical for video amplifiers; and while three-tube feedback{sup 3} is feasible on theoretical grounds, it is difficult to ...
Date: March 16, 1949
Creator: Fitch, V.
Partner: UNT Libraries Government Documents Department

LOW FREQUENCY AMPLIFIER IH-130-1

Description: The design of a transistorized d-c coupled amplifier having very good gain stability and low drift of the output d-c level is described. Low-frequency input signals from a low-impedance source are amplified by the system to an approximate peak-to-peak amplitude of 4 v. (J.R.D.)
Date: October 23, 1961
Creator: Llacer, J.
Partner: UNT Libraries Government Documents Department

Spectral analysis of reltivistic bunched beams

Description: Particles in a storage ring are oscillating in the longitudinal and transverse dimensions, and therefore, the frequency domain is natural for analyzing many beam generated signals. Information ranging from oscillation frequencies to beam phase space distributions can be extracted from the spectral content of these signals. The spectrum of a single particle is like a Green`s function, and it is the key to understanding the spectrum produced by a beam. Three separate cases are consider in an order of increasing complexity: (1) constant revolution frequency, (2) Frequency Modulation introduced by synchrotron oscillations, and (3) Amplitude Modulation introduced by betatron oscillations.
Date: May 1, 1996
Creator: Siemann, R.H.
Partner: UNT Libraries Government Documents Department

General Cause of Sheath Instability Identified for Low Collisionality Plasma in Devices with Secondary Electron Emission

Description: A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ~20MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport.
Date: May 11, 2012
Creator: M.C. Campanell, A. Khrabrov and I Kaganovich
Partner: UNT Libraries Government Documents Department

Simulation of Non-resonant Internal Kink Mode with Toroidal Rotation in NSTX

Description: Plasmas in spherical and conventional tokamaks, with weakly reversed shear q pro le and minimum q above but close to unity, are susceptible to an non-resonant (m, n ) = (1, 1) internal kink mode. This mode can saturate and persist and can induce a (2; 1) seed island for Neoclassical Tearing Mode (NTMs)1 . The mode can also lead to large energetic particle transport and signi cant broadening of beam-driven current. Motivated by these important e ects, we have carried out extensive nonlinear simulations of the mode with nite toroidal rotation using parameters and pro les of an NTSX plasma with a weakly reversed shear pro le. The numerical results show that, at the experimental level, plasma rotation has little e ect on either equilibrium or linear stability. However, rotation can signi cantly inuence the nonlinear dynamics of the (1, 1) mode and the the induced (2, 1) magnetic island. The simulation results show that a rotating helical equilibrium is formed and maintained in the nonlinear phase at nite plasma rotation. In contrast, for non-rotating cases, the nonlinear evolution exhibits dynamic oscillations between a quasi-2D state and a helical state. Furthermore, the e ects of rotation are found to greatly suppress the (2, 1) magnetic island even at a low level.
Date: July 16, 2013
Creator: Fu, Guoyong
Partner: UNT Libraries Government Documents Department

Direct focusing error correction with ring-wide TBT beam position data

Description: Turn-By-Turn (TBT) betatron oscillation data is a very powerful tool in studying machine optics. Hundreds and thousands of turns of free oscillations are taken in just few tens of milliseconds. With beam covering all positions and angles at every location TBT data can be used to diagnose focusing errors almost instantly. This paper describes a new approach that observes focusing error collectively over all available TBT data to find the optimized quadrupole strength, one location at a time. Example will be shown and other issues will be discussed. The procedure presented clearly has helped to reduce overall deviations significantly, with relative ease. Sextupoles, being a permanent feature of the ring, will need to be incorporated into the model. While cumulative effect from all sextupoles around the ring may be negligible on turn-to-turn basis it is not so in this transfer line analysis. It should be noted that this procedure is not limited to looking for quadrupole errors. By modifying the target of minimization it could in principle be used to look for skew quadrupole errors and sextupole errors as well.
Date: March 1, 2011
Creator: Yang, M.J.
Partner: UNT Libraries Government Documents Department

Ambient beam motion and its excitation by ghost lines in the Tevatron

Description: Transverse betatron motion of the Tevatron proton beam is measured and analyzed. It is shown that the motion is coherent and excited by external sources of unknown origins. Observations of the time-varying 'ghost lines' in the betatron spectrum are reported. The direct measurement of the rms betatron oscillations amplitude estimates it at about 110 nm at {beta}{sub y} {approx} 900 m. Correspondingly, at the amplitudes at the average beta function location with {beta}{sub y} {approx} 50 m is about 25 nm. Given that such direct measurements with clearly observable betatron peak were not repeatedly reproducible, one can conclude that well know 'ghost lines' are the reason for that - as they are come and go without any obvious regularity. Our analysis of these 'ghost lines' shows that (a) besides slow motion across frequencies, they also exhibit oscillatory movements with period varying from 15-20 min to few hours; (b) for the stores analysed, the lines add about factor of 2 to average - over colliding store duration - Schottky power in the betatron bands. The latter allows to estimate that they contribute about half to the previously determined the rms normalized emittance growth rate of some 0.06 {pi} mm mrad/hr. The Tevatron 'ghost lines' look very similar to infamous 'humps' recently observed in the LHC. Those 'humps' are unwanted oscillations seen repeatedly in the LHC beams (mostly in the vertical plane) and also believed to be caused by external excitations.
Date: March 1, 2011
Creator: Shiltsev, V.
Partner: UNT Libraries Government Documents Department

TRANSVERSE COHERENT RESISTIVE INSTABILITIES OF AZIMUTHALLY BUNCHED BEAMS IN PARTICLE ACCELERATORS

Description: The transverse electromagnetic coupling of bunches of particles with each other is investigated theoretically, and shown to incorporate the possibility (due to the effect of nonperfectly conducting vacuum chamber walls) of coherent instability even when the longitudinal distance between bunches is much larger than the transverse dimensions of the vacuum tank. The modes of oscillation in which the bunches move rigidly are investigated; criteria for stability, and expressions for the small amplitude growth rates under unstable conditions are presented. The case of a single bunch is considered in detail and demonstrated to be stable (even in the absence of landau damping) provided {nu} lies between an integer and the next higher half-integer, where {nu} is the number of transverse free betatron oscillations occurring in one revolution; for many bunches which are sensibly different in intensity (a criterion for this is presented), all modes are stable provided {nu} satisfies the same restriction. For equally spaced bunches of equal numbers of particles, approximately half the modes are unstable without Landau damping. Numerical examples are presented covering some intermediate situations.
Date: April 1, 1966
Creator: Courant, Ernest D. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Three-dimensional Numerical Investigation of Electron Transport with Rotating Spoke in a Cylindrical Anode Layer Hall Plasma Accelerator

Description: The oscillation behavior described in [Tang et. al, Phys. Plasmas 19, 073519 (2012)] di ers too greatly from previous experimental and numerical studies to claim observation of the same phenomenon. Most signi cantly, the rotation velocity in [Tang et. al, Phys. Plasmas 19, 073519 (2012)] is three orders of magnitude larger than that of typical \rotating spoke" phenomena. Several physical and numerical considerations are presented to more accurately understand the numerical results of [Tang et. al, Phys. Plasmas 19, 073519 (2012)] in light of previous studies.
Date: August 27, 1012
Creator: Ellison, C. Leland; Matyash, K.; Parker, J. B.; Raitses, Y. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department

Polarized proton experiment in the AGS with a partial snake

Description: In three polarized proton runs at the AGS it was recently shown that the imperfection depolarizing resonances in the AGS can be overcome with a 5% partial snake and the intrinsic depolarizing resonances could be jumped with the pulsed tune-jump quadrupoles even in the presence of the partial snake. For the first time polarized proton beam was accelerated up to the required RHIC injection energy of 25 GeV. No polarization was lost due to the imperfection resonances and the depolarization from most intrinsic resonances was avoided with the tune-jump quadrupoles. However, significant amount of polarization was lost at 0+{nu}{sub y}, 12+{nu}{sub y} and 36+{nu}{sub y}, which is believed to be partially due to coupling resonances. A novel energy-jump method and other new schemes to overcome the coupling and intrinsic resonances are discussed.
Date: December 1, 1996
Creator: Huang, H.; Ahrens, L. & Alessi, J.G.
Partner: UNT Libraries Government Documents Department

Transverse modes of a bunched beam at space charge dominating impedance

Description: Coherent transverse oscillations of a bunched beam are considered at space charge dominated impedance and synchrotron motion taken into account. General equation for the bunch eigenmodes is derived, its exact analytical solution is found for a boxcar bunch at linear synchrotron oscillations, and numerical solutions are presented for other distributions. Both low and high synchrotron frequency approaches are considered and compared, fields of their application are established, and some estimations are proposed for the intermediate region.
Date: June 1, 2009
Creator: Balbekov, V.
Partner: UNT Libraries Government Documents Department

Stability of bunched beams against high order nonlinear resonances

Description: For a given tune, beams can be made stable against the effects of isolated high order resonances. However, in a system whose betatron tune is changing, there exists a mechanism for beam loss. This mechanism is discussed and applied to the case of bunched beams, where the synchrotron motion introduces a time variation of tune. A stability criterion for a system with varying tune is presented, together with a set of suggested parameter values. The basic constraint is that the linear tune spread in the bunches (arising through the chromaticity) be smaller than the nonlinear tune spread (arising from the nonlinearities of magnetic field as well as the beam-beam interaction). This can be achieved with a small chromaticity and a relatively large nonlinear term causing a tune spread with betatron amplitude. Specific values for chromaticity and nonlinearity are suggested. A limit on the resonance excitation strength is also given. Since the beam-beam interaction introduces a tune spread with amplitude, then in some range it is found to have a stabilizing influence insofar as isolated high order nonlinear resonances are concerned. This point is discussed together with a brief discussion on the onset of stochastic phenomena, which are due to the interaction of many resonances. It is concluded that with the given set of parameters, bunched beams stable against high order nonlinear resonances can be achieved. (auth)
Date: December 1, 1973
Creator: Month, M.
Partner: UNT Libraries Government Documents Department