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Beam energy absolute measurement using K-edge absorption spectrometers

Description: A method is presented of absolute energy measurement with an accuracy of {triangle}{Epsilon} {approximately} 10{sup {minus}4}{Epsilon}{sub o} by direct measurement of the bend angle in a high-precision magnetic dipole using two opposite-direction short (about 2 mm long) high-field-intensity magnets ({bar {Beta}} {sub dipole} {much_lt} {Beta}{sub short mag}) installed at each end and two K-edge absorption spectrometers. Using these spectrometers and the hard x-ray synchrotron radiation created by the short magnets, a bend angle of 4.5 arc deg for the CEBAF energy bandwidth can be measured with an accuracy of a few units of 10{sup {minus}6} rad, and the main sources of systematic errors are the absolute measurement of the field integral and the determination of the centroid of the synchrotron beam at a wavelength equal to the K-edge absorption of the chosen substance.
Date: May 1, 1994
Creator: Karabekov, I.P. & Neil, G.
Partner: UNT Libraries Government Documents Department

Amplitude and phase beam characterization using a two-dimensional wavefront sensor

Description: We have developed a two-dimensional Shack-Hartman wavefront sensor that uses binary optic lenslet arrays to directly measure the wavefront slope (phase gradient) and amplitude of the laser beam. This sensor uses an array of lenslets that dissects the beam into a number of samples. The focal spot location of each of these lenslets (measured by a CCD camera) is related to the incoming wavefront slope over the lenslet. By integrating these measurements over the laser aperture, the wavefront or phase distribution can be determined. Since the power focused by each lenslet is also easily determined, this allows a complete measurement of the intensity and phase distribution of the laser beam. Furthermore, all the information is obtained in a single measurement. Knowing the complete scalar field of the beam allows the detailed prediction of the actual beam`s characteristics along its propagation path. In particular, the space- beamwidth product M{sup 2}, can be obtained in a single measurement. The intensity and phase information can be used in concert with information about other elements in the optical train to predict the beam size, shape, phase and other characteristics anywhere in the optical train. We present preliminary measurements of an Ar{sup +} laser beam and associated M{sup 2} calculations.
Date: September 1996
Creator: Neal, D. R.; Alford, W. J.; Gruetzner, J. K. & Warren, M. E.
Partner: UNT Libraries Government Documents Department

Developments on the Toroid Ion Trap Analyzer

Description: Investigations into several areas of research have been undertaken to address the performance limitations of the toroid analyzer. The Simion 3D6 (2) ion optics simulation program was used to determine whether the potential well minimum of the toroid trapping field is in the physical center of the trap electrode structure. The results (Figures 1) indicate that the minimum of the potential well is shifted towards the inner ring electrode by an amount approximately equal to 10% of the r0 dimension. A simulation of the standard 3D ion trap under similar conditions was performed as a control. In this case, the ions settle to the minimum of the potential well at a point that is coincident with the physical center (both radial and axial) of the trapping electrodes. It is proposed that by using simulation programs, a set of new analyzer electrodes can be fashioned that will correct for the non- linear fields introduced by curving the substantially quadrupolar field about the toroid axis in order to provide a trapping field similar to the 3D ion trap cross- section. A new toroid electrode geometry has been devised to allow the use of channel- tron style detectors in place of the more expensive multichannel plate detector. Two different versions have been designed and constructed - one using the current ion trap cross- section (Figure 2) and another using the linear quedrupole cross- section design first reported by Bier and Syka (3).
Date: June 13, 1999
Creator: Lammert, S.A.; Thompson, C.V. & Wise, M.B.
Partner: UNT Libraries Government Documents Department

Laser-heterodyne interferometry with streak camera detection

Description: The spatial interference pattern between a cw laser local oscillator and a pulsed laser (40 to 80 ns pulsewidth) is recorded by an electronic streak camera. Analysis yields time dependent wavefront and frequency chirp characteristics of single laser pulses. 2 refs., 3 figs.
Date: January 1, 1988
Creator: Feldman, M.; Salmon, J.T. & Mockler, D.
Partner: UNT Libraries Government Documents Department

Analyzing gigahertz bunch length instabilities with a digital signal processor

Description: A bunch length instability, nicknamed the ``sawtooth``, because of its transient behavior, has been observed at high current running in the Stanford Linear Collider (SLC) electron damping ring. The incompatibility of this instability with successful SLC naming prompted its study using a high bandwidth real-time spectrum analyzer, the Tektronix 3052 digital signal processor (DSP) system. This device has been used to study energy ramping in storage rings but this is the first time it has been used to study transient instability phenomena. It is a particularly valuable tool for use in understanding non-linear, multiple frequency phenomena. The frequency range of this device has been extended through the use of radio frequency (RF) down converters. This paper describes the measurement setup and presents some of the results.
Date: November 1, 1992
Creator: Stege, R. E. Jr.; Krejcik, P. & Minty, M. G.
Partner: UNT Libraries Government Documents Department

High resolving power spectrometer for beam analysis

Description: We describe a system designed to analyze the high energy, closely spaced bunches from individual RF pulses. Neither a large solid angle nor momentum range is required so this allows characteristics that appear useful for other applications such as ion beam lithography. The spectrometer is a compact, double-focusing QBQ design whose symmetry allows the Quads to range between F or D with a correspondingly large range of magnifications, dispersion and resolving power. This flexibility insures the possibility of spatially separating all of the bunches along the focal plane with minimal transverse kicks and bending angle for differing input conditions. The symmetry of the system allows a simple geometric interpretationof the resolving power in terms of thin lenses and ray optics. We discuss the optics and the hardware that is proposed to measure emittance, energy, energy spread and bunch length for each bunch in an RF pulse train for small bunch separations. We also discuss how to use such measurements for feedback and feedforward control of these bunch characteristics as well as maintain their stability. 2 refs.
Date: March 1, 1992
Creator: Moshammer, H. W. & Spencer, J. E.
Partner: UNT Libraries Government Documents Department

Latency differences and effects of selective attention to gratings in the central and right visual fields: II

Description: The goals were to examine the temporal sequence in which visual information (such as visual field, spatial frequency) are processed and to determine whether different neural sources are activated when such features are attended versus not attended. These issues are basic to current models of visual selective attention. 10 refs., 4 figs.
Date: January 1, 1987
Creator: Aine, C.J.; George, J.S. & Flynn, E.R.
Partner: UNT Libraries Government Documents Department

Bragg reflection transmission filters for variable resolution monochromators

Description: There are various methods for improving the angular and spectral resolution of monochromator and analyzer systems. The novel system described here, though limited to higher x-ray energies (>20keV), is based on a dynamical effect occurring on the transmitted beam with a thin perfect crystal plate set in the Bragg reflection case. In the case of Bragg reflection from a perfect crystal, the incident beam is rapidly attenuated as it penetrates the crystal in the range of reflection. This extinction length is of the order of microns. The attenuation length, which determines the amount of normal transmission through the plate is generally much longer. Thus, in the range of the Bragg reflection the attenuation of the transmitted beam can change by several orders of magnitude with a small change in energy or angle. This thin crystal plate cuts a notch in the transmitted beam with a width equal to its Darwin width, thus acting as a transmission filter. When used in a non-dispersive mode with other monochromator crystals, the filter when set at the Bragg angle will reflect the entire Darwin width of the incident beam and transmit the wings of the incident beam distribution. When the element is offset in angle by some fraction of the Darwin width, the filter becomes useful in adjusting the angular width of the transmitted beam and removing a wing. Used in pairs with a symmetric offset, the filters can be used to continuously adjust the intrinsic angular divergence of the beam with good wing reduction. Instances where such filters may be useful are in improving the angular resolution of a small angle scattering camera. These filters may be added to a Bonse-Hart camera with one pair on the incident beam to reduce the intrinsic beam divergence and a second pair on the analyzer arm ...
Date: January 1, 1989
Creator: Chapman, D. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

Microchannel plate based detector for a heavy ion beam spectrometer

Description: The design parameters and operating characteristics of the detector used in the Brutus and Fannie heavy ion beam spectrometers at the SuperHILAC facility are described. The detector utilizes a 25 mm diameter microchannel plate array to obtain gains of 10/sup 2/ to 10/sup 8/ with a linear dynamic range of 10/sup 3/. It has had over three years of almost maintenance-free service, detecting ion beams from carbon to xenon with energies between 1.2 and 8.5 MeV per nucleon.
Date: October 1, 1979
Creator: Green, M.I.
Partner: UNT Libraries Government Documents Department

High resolving power spectrometer for beam analysis

Description: We describe a system designed to analyze the high energy, closely spaced bunches from individual RF pulses. Neither a large solid angle nor momentum range is required so this allows characteristics that appear useful for other applications such as ion beam lithography. The spectrometer is a compact, double-focusing QBQ design whose symmetry allows the Quads to range between F or D with a correspondingly large range of magnifications, dispersion and resolving power. This flexibility insures the possibility of spatially separating all of the bunches along the focal plane with minimal transverse kicks and bending angle for differing input conditions. The symmetry of the system allows a simple geometric interpretationof the resolving power in terms of thin lenses and ray optics. We discuss the optics and the hardware that is proposed to measure emittance, energy, energy spread and bunch length for each bunch in an RF pulse train for small bunch separations. We also discuss how to use such measurements for feedback and feedforward control of these bunch characteristics as well as maintain their stability. 2 refs.
Date: March 1, 1992
Creator: Moshammer, H.W. & Spencer, J.E.
Partner: UNT Libraries Government Documents Department

Visual evoked responses to sinusoidal gratings presented in central and right visual fields: I

Description: The present study applies neuromagnetic measurement techniques to probe the neurophysiological processing of spatial frequency (SF) by normal human observers. By exploiting the temporal and spatial resolution of neuromagnetic measurements, we hope to discriminate and characterize underlying neural functions and explore their correlation with perceptual or behavioral performance measures. Spatial frequency analysis has proven a useful paradigm for the study of visual perception and has been applied in psychophysical studies as well as invasive anatomical and physiological studies of experimental animals. These approaches have produced evidence of specialized neural activity and network structure for the analysis of spatial frequency information. Because the encoding of spatial frequency is a function of neuronal receptive-field size and since receptive-field size varies as a function of retinal location, we have also examined effects of visual field on responses to stimuli of defined spatial frequency content. 10 refs., 3 figs.
Date: January 1, 1987
Creator: George, J.S.; Aine, C.J. & Flynn, E.R.
Partner: UNT Libraries Government Documents Department

Analyzing gigahertz bunch length instabilities with a digital signal processor

Description: A bunch length instability, nicknamed the sawtooth'', because of its transient behavior, has been observed at high current running in the Stanford Linear Collider (SLC) electron damping ring. The incompatibility of this instability with successful SLC naming prompted its study using a high bandwidth real-time spectrum analyzer, the Tektronix 3052 digital signal processor (DSP) system. This device has been used to study energy ramping in storage rings but this is the first time it has been used to study transient instability phenomena. It is a particularly valuable tool for use in understanding non-linear, multiple frequency phenomena. The frequency range of this device has been extended through the use of radio frequency (RF) down converters. This paper describes the measurement setup and presents some of the results.
Date: November 1, 1992
Creator: Stege, R.E. Jr.; Krejcik, P. & Minty, M.G.
Partner: UNT Libraries Government Documents Department

Gaussian optics calculations of the parameters of a magnetic sector energy analyzer

Description: The design of a magnetic deflection system for use as an electron energy loss spectrometer can be a complex process if one takes the most general approach. However, for application to materials research the design process can be reduced to three basic steps. First, the qualitative features of the overall system are defined--i.e., incident electron energy, required resolution, type of magnet, the desired focal properties, etc. Secondly, the design parameters necessary to meet these requirements are calculated using the appropriate equations. Finally, once the magnetic field has been specified, ray-tracing techniques can be employed to verify the system response to the conditions defined in the first two steps. The calculation of the parameters of a uniform field magnetic sector analyzer capable of energy resolutions of 20 ppM or better are considered. Higher resolution is attainable; however, for most materials work, more important considerations are the attainment of double focusing to improve S/N, the minimization of aberrations and the achievement of a flat image plane to facilitate parallel data recording.
Date: January 1, 1978
Creator: Zaluzec, N.J.
Partner: UNT Libraries Government Documents Department

Optical diagnostics in the advanced test accelerator (ATA) environment

Description: The ATA is a 50-MeV, 10-kA, 70-ns pulsed electron beam accelerator that generates an extremely harsh environment for diagnostic measurements. Diagnostic targets placed in the beamline are subject to damage, frequently being destroyed by a single pulse. High radiation (x-ray, gamma, and neutron) and electromagnetic interference levels preclude placing components near the beamline that are susceptible to radiation damage. Examples of such components are integrated circuit elements, hydrocarbons such as Teflon insulation, and optical components that darken, resulting in transmission loss. Optical diagnostics play an important part in measuring experimental parameters such as the beam current density profile. A large number of optical lines of sight (LOS) are routinely deployed along the experimental beamlines that use the ATA beam. Gated TV cameras are located outside the accelerator tunnel, because the tunnel is inaccessible during operations. We will describe and discuss the difficulties, problems, and solutions encountered in making optical measurements in the ATA environment.
Date: May 1, 1987
Creator: Chong, Y.P.; Cornish, J.P. & Donnelly, D.
Partner: UNT Libraries Government Documents Department

A novel method for measuring beam energies by time-of-flight

Description: A novel time-of-flight (TOF) technique is reported for the measurement of ion beam energies. This technique was used, along with a more conventional nuclear reaction technique, to measure the calibration function of the Holifield Heavy Ion Research Facility tandem accelerator energy-analyzing magnet. The technique to be described is based on the use of a variable frequency buncher and two identical capacitive pickup units (CPU) to measure the velocity of ions selected by the energy-analyzing magnet. The CPUs were separated by a distance of 6166.2 +- 0.4 mm and were connected by equal length cables to wide band HP-8447F preamplifiers which in turn were connected to a dual trace oscilloscope. The beam was bunched using the first harmonic element of the double-drift bunching system which is located in the tandem accelerator injection line.
Date: January 1, 1986
Creator: Olsen, D.K.; Erb, K.A.; Jones, C.M.; Milner, W.T. & Ziegler, N.F.
Partner: UNT Libraries Government Documents Department

Large-acceptance-angle gridded analyzers in an axial magnetic field

Description: Electrostatic retarding-potential gridded analyzers have been used to measure the current and the axial energy distributions of ions escaping along magnetic field lines in the 2XIIB magnetic mirror fusion experiment at Lawerence Livermore National Laboratory (LLNL). Three analyzers are discussed: a large scanning analyzer with a movable entrance aperture that can measure ion or electron losses from a different segment of the plasma diameter on each shot, a smaller analyzer that mounts in 5-cm-diam ports, and a multicollector analyzer that can continuously measure losses from the entire plasma diameter.
Date: June 1, 1981
Creator: Molvik, A.W.
Partner: UNT Libraries Government Documents Department

An improved time-of-flight ion charge state diagnostic

Description: A time-of-flight diagnostic for analysis of relatively low energy ion beams is described. The system incorporates several novel features which improve its performance in a number of ways. The technique is simple and can provide an alternative to magnetic analysis of ion beams for the determination of ion charge state and beam composition.
Date: March 1, 1987
Creator: Brown, I.G.; Galvin, J.E.; MacGill, R.A. & Wright, R.T.
Partner: UNT Libraries Government Documents Department

An interference wiggler for precise diagnostics of electron beam energy

Description: Relativistic electrons passing through two identical magnetic sections generate synchrotron radiation whose spectrum is strongly modulated as the photon energy varies. The modulation is caused by the interference of radiation from each section, and has been observed in the spectrum of spontaneous radiation from transverse optical klystron which utilizes two undulators. In this paper, another device based on two simple wigglers is analyzed. The device, which will be called the interference wiggler, can be used for precise diagnostics of electron beam energy; by analyzing the modulated spectrum with a monochromator, the electron energy can be determined up to an accuracy of 10/sup -3/ or 10/sup -4/. General design criteria for interference wigglers are developed. Several example designs are given for measurement of the electron energy for the planned electron beam facility at CEBAF for the 1 to 2 GeV Light Source at Berkeley.
Date: March 1, 1987
Creator: Kim, Kwang-Je
Partner: UNT Libraries Government Documents Department

E/parallels/B end-loss-ion analyzer for TMX-U

Description: We are constructing and testing a diagnostic intrument to investigate, in detail, ions emanating along magnetic-field lines from the plasma region of the TMX-U tandem-mirror experiment. This analyzer (of TFTR design) contains parallel electric and magnetic fields, which yield ion mass and energy spatial separation, respectively. A two-dimensional array of 128 copper collector plates detects the particles. The entering ion flux is first well collimated and then focused onto the detector plane during the 180/sup 0/ bending in the magnetic field. This instrument is designed to measure higher particle energies than the present gridded end-loss analyzers as well as determine the energy spectra more accurately. Tandem-mirror plasma parameters to be investigated with this analyzer include end-plug potential, average central-cell-ion energy, and plasma potential in the thermal-barrier and nearby regions. We plan a time resolution of up to 2 kHz for each detector.
Date: September 14, 1984
Creator: Foote, J.H.; Coutts, G.W.; Pedrotti, L.R.; Schlander, L. & Wood, B.E.
Partner: UNT Libraries Government Documents Department

Tune measurement in the APS ring

Description: The APS system will contain three rings. The first is a positron accumulator ring (PAR). Its function is to coalesce 24, 30-ns-long positron bunches into one 290-ps bunch. The second is the injector synchrotron (IS). It accelerates the 450-MeV positron bunches to 7 Gev for injection into the storage ring (SR). Betatron and synchrotron motion frequently occurs in circular machines, without any deliberate excitation. However, the amplitudes of this motion cannot be predicted. Therefore, it is desirable to have controlled ways to excite these modes. Two types of devices will be used to excite the beam. One will be a magnetic kicker or bumper. All rings already have these devices planned for the horizontal direction for injecting and extracting beams. Some of these magnets will be used for exiting horizontal betatron motion. In the storage ring, a special kicker will be installed to produce up to 1 mm amplitude motion in the vertical direction. Two 8.4-in striplines (SL) (1/4 wavelength at 352 MHz) will be installed on all rings. One stripline in each ring will be used to drive all three tunes, and the other stripline will be used as a pickup. In the PAR and IS, the pickup stripline will be in a dispersive region. This will allow observation of both betatron and synchrotron motions. In the SR, the stripline will be in a nondispersive region because it is not practical to install it in a dispersive region. To do synchrotron tune measurements in the SR, one of the button BPMs located in a dispersive region will be used. To minimize development effort, as much of the BPM system electronics as possible will be used in the tune measurement system. The BPM electronics uses the AMP/PM conversion technique. This system operates at 352 MHz. Thus, tune measurement components were ...
Date: July 1, 1993
Creator: Sellyey, W.; Kahana, E. & Wang, X.
Partner: UNT Libraries Government Documents Department

A criterion for the dynamical to kinematical transition of x-ray diffraction on a bent crystal

Description: It is well known that the peak reflectivity of a bent crystal, generally speaking, is smaller than that of a plane crystal, and it goes to zero when the crystal curvature goes to infinity. The reason for this is the transition between dynamical and kinematical diffraction that takes place as the crystal curvature increases. The physical explanation is as follows: the deviation from exact Bragg position along the beam changes so fast that the thickness over which the beam is within a Darwin width becomes too small to reflect the beam. Bent crystals are widely used as focusing elements in X-ray optics, and estimation of whether or not a bent crystal is still perfect enough to provide good reflectivity is of great importance. Currently the Advanced Photon Source (APS) is considering a number of bent crystals as focusing elements for future APS beamlines, including a sagittaly focusing monochromator and bent backscattering analyzer for inelastic X-ray scattering experiments. A criterion is given in answer to the question: To what extent is it possible to bend a crystal without loss of X-ray peak reflectivity? An expression based on the work of Chukhovskii, Gabrielyan and Petrashen, is formulated that applies to anisotropic cubic crystal and that can be used not only for conventional asymmetric Bragg diffraction, but also for inclined crystal diffraction. The following special cases are treated as examples: isotropic crystal, standard symmetrical Bragg diffraction, extremely asymmetric diffraction, and backscattering with Bragg angles near 90{degree}. In addition, an asymptotic behavior for high energies is detailed.
Date: September 1, 1993
Creator: Kushnir, V. I. & Macrander, A. T.
Partner: UNT Libraries Government Documents Department