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Disruption effects on the beam size measurement

Description: At the SLC Final Focus with higher currents and smaller beam sizes, the disruption parameter D{sub y} is close to one and so the pinch effect should produce a luminosity enhancement. Since a flat beam-beam function is fit to deflection scan data to measure the beam size, disruption can affect the measurement. Here the authors discuss the quantitative effects of disruption for typical SLC beam parameters. With 3.5 10{sup 10} particles per pulse, bunch length of 0.8 mm and beam sizes of 2.1 {mu}m horizontally and 0.55 {mu}m vertically, the measured vertical size can be as much as 25% bigger than the real one. Furthermore during the collision the spot size actually decrease, producing an enhancement factor H{sub D} of about 1.25. This would yield to a true luminosity which is 1.6 times that which is estimated from the beam-beam deflection fit.
Date: June 1, 1995
Creator: Raimondi, P.; Decker, F.J. & Chen, P.
Partner: UNT Libraries Government Documents Department

Simulation studies of the LAMPF proton linac

Description: The LAMPF accelerator consists of two 0.75-MeV injectors, one for H{sup +} and the other for H{sup {minus}}, a separate low-energy beam transport (LEBT) line for each beam species, a 0.75 to 100-MeV drift-tube linac (DTL) operating at 201.25-MHz, a 100-MeV transition region (TR), and a 100 to 800-MeV side-coupled linac (SCL) operating at 805-MHz. Each LEBT line consists of a series of quadrupoles to transport and transversely match the beam. The LEBT also contains a prebuncher, a main buncher, and an electrostatic deflector. The deflector is used to limit the fraction of a macropulse which is seen by the beam diagnostics throughout the linac. The DTL consists of four rf tanks and uses singlet FODO transverse focusing. The focusing period is doubled in the last two tanks by placing a quadrupole only in every other drift-tube. Doublet FDO transverse focusing is used in the SCL. The TR consists of separate transport lines for the H{sup +} and H{sup {minus}} beams. The pathlengths for the two beams differ, by introducing bends, so as to delay arrival of one beam relative to the other and thereby produce the desired macropulse time structure. Peak beam currents typically range from 12 to 18-mA for varying macropulse lengths which give an average beam current of 1-mA. The number of particles per bunch is of the order 10{sup 8}. The work presented here is an extension of previous work. The authors have attempted to do a more complete simulation by including modeling of the LEBT. No measurements of the longitudinal structure of the beam, except phase-scans, are performed at LAMPF. The authors show that, based on simulation results, the primary causes of beam spill are inefficient longitudinal capture and the lack of longitudinal matching. Measurements to support these claims are not presently made at LAMPF. ...
Date: May 1, 1995
Creator: Garnett, R.W.; Gray, E.R.; Rybarcyk, L.J. & Wangler, T.P.
Partner: UNT Libraries Government Documents Department

High power beam profile monitor with optical transition radiation

Description: A simple monitor has been built to measure the profile of the high power beam (800 kW) delivered by the CEBAF accelerator at Jefferson Lab. The monitor uses the optical part of the forward transition radiation emitted from a thin carbon foil. The small beam size to be measured, about 100 {mu}m, is challenging not only for the power density involved but also for the resolution the instrument must achieve. An important part of the beam instrumentation community believes the radiation being emitted into a cone of characteristic angle 1/{gamma} is originated from a region of transverse dimension roughly {lambda}{gamma}; thus the apparent size of the source of transition radiation would become very large for highly relativistic particles. This monitor measures 100 {mu}m beam sizes that are much smaller than the 3.2 mm {lambda}{gamma} limit; it confirms the statement of Rule and Fiorito that optical transition radiation can be used to image small beams at high energy. The present paper describes the instrument and its performance. The authors tested the foil in, up to 180 {mu}A of CW beam without causing noticeable beam loss, even at 800 MeV, the lowest CEBAF energy.
Date: June 1, 1997
Creator: Denard, J.C.; Piot, P.; Capek, K. & Feldl, E.
Partner: UNT Libraries Government Documents Department

Stability and halo formation in axisymmetric intense beams

Description: Beam stability and halo formation in high-intensity axisymmetric 2D beams in a uniform focusing channel are analyzed using particle-in-cell simulations. The tune depression-mismatch space is explored for the uniform (KV) distribution of the particle transverse-phase-space density, as well as for more realistic ones (in particular, the water-bag distribution), to determine the stability limits and halo parameters. The numerical results show an agreement with predictions of the analytical model for halo formation.
Date: October 1, 1997
Creator: Gluckstern, R.L. & Kurennoy, S.S.
Partner: UNT Libraries Government Documents Department


Description: In the Relativistic Heavy ion Collider (RHIC) much larger background signals were occurring at BRAMS, one of the four experiments. This was especially pronounced at the time when vacuum conditions deteriorated due to the beam ionization profile monitor replacements. Recording the beam intensities during the store provided the beam lifetime. Predictions from the beam gas interactions to the above measured values are compared The ionization gauges simultaneously recorded the vacuum pressure data.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Cumulative Beam Breakup in Linear Accelerators with Arbitrary Beam Current Profile

Description: An analytic formalism for the solution of cumulative beam breakup in linacs with arbitrary beam current profile is developed. It is applied to obtain an expression for the transverse displacement of trains of bunches of finite length.The same formalism is used to investigate the beam breakup-enhanced displacement of beams caused by the misalignment of the deflecting structures or focusing elements.
Date: June 1, 2001
Creator: Delayen, J.R.
Partner: UNT Libraries Government Documents Department


Description: During the year 2000 run a total of eight beam scans (Vernier Scans) were performed at various interaction points (IF) at RHIC. During a Vernier Scan the experimental collision rates are recorded while the beams are stepwise scanned across each other. Vernier Scans yield transverse beam sizes as well as maximum luminosity and thus the absolute cross section, which with the limited data from the 2000 run we measured to be {sigma} = 8.9 {+-} 0.3 barn at ({radical}s{sub NN}) = 130 GeV. Also, Vernier Scans permit performance studies of the beam orbit control and local coupling.
Date: June 18, 2001
Creator: DREES,A. & XU,Z.
Partner: UNT Libraries Government Documents Department


Description: The 6.7-MeV, 100-mA proton beam being produced in the Low Energy Demonstration Accelerator (LEDA) RFQ will be injected into a 52-magnet lattice in order to study the formation of beam halo [1]. The LEDA RFQ beam has a rms size of 1 mm. At nine longitudinal locations along the lattice an assembly that incorporates both a wire scanner and a halo-scraper assembly will be placed to make current density measurements of the beam.
Date: October 1, 2000
Partner: UNT Libraries Government Documents Department

Status of flat electron beam production

Description: Last year at LINAC2000 [1] the authors reported their initial verification of the round beam (comparable transverse emittances) to flat beam (high transverse emittance ratio) transformation described by Brinkmann, Derbenev, and Floettmann [2]. Further analysis of the data has confirmed that a transverse emittance ratio of approximately 50 was observed. Graphics representing observational detail are included here, and future plans outlined.
Date: August 24, 2001
Creator: al., Donald A. Edwards et
Partner: UNT Libraries Government Documents Department

Roll bar x-ray spot size measurement technique

Description: A time dependent x-ray spot size measurement is critical to understanding beam target physics such as target plasma generated beam instabilities. The so-called roll bar measurement uses a heavy metal material which is optically thick to X-rays, to form a 1D shadow of the x-ray origination spot. This spot is where an energetic electron beam interacts with a high Z target to produce the x-rays. The material (the �roll bar�) has a slight radius to avoid alignment problems. If a beam profile is assumed (or measured by other means), the equivalent x-ray spot size can be calculated from the x-ray shadow cast by the roll bar. Typically a radiographic film is exposed over the duration of the beam pulse, and the shadow is analyzed for a time integrated measurement. This paper explores various techniques to convert the x-rays to visible photons which can be imaged using a gated camera or streak camera for time evolved x-ray spot size. Data will be presented from the measurements on the ETA II induction linac.
Date: August 14, 1998
Creator: Houck, T L & Richardson, R A
Partner: UNT Libraries Government Documents Department


Description: Two different parameters for the quantitative description of beam halo are introduced, both based on moments of the particle distribution. One parameter is a measure of spatial halo formation and has been defined previously by Wangler and Crandall [3], termed the profile parameter. The second parameter relies on kinematic invariants to quantify halo formation in phase space; we call it the halo parameter. The profile parameter can be computed from experimental beam profile data. The halo parameter provides a theoretically more complete description of halo in phase space, but is difficult to obtain experimentally.
Date: June 1, 2001
Creator: ALLEN, C.K. & WANGLER, T.P.
Partner: UNT Libraries Government Documents Department


Description: In the Spallation Neutron Source (SNS) ring, multi-turn injection is employed to obtain a large transverse beam size which significantly reduces the space-charge tune shift of the accumulated beam. Careful choice of the painting scheme and bump function is required to obtain the desired beam profile together with low beam loss. In this paper we examine, both analytically and numerically, the effect of the space charge on the beam profile during multi-turn injection painting.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department


Description: A method to split off a few percent of the 6 x 10{sup 13} AGS beam delivered to the Slow External Beam (SEB) lines and send it down the Fast External Beam line (FEB) has been developed. The mission is to feed a counter experiment off the FEB that directly measures the neutrino mass using the muon storage ring. The use of normal thin septum splitters would have an excessive loss overhead and been optically difficult. The AGS Slow Extraction uses a third integer resonance with sextuple strength so the resonance width is a few percent of the beam width. This results in a low density tail which will be clipped by a bent crystal and deflected into the FEB channel. This clipping off of the tail should reduce losses in the SEB transport line. Details of modeled orbits, particle distribution and extraction trajectories into and out off the crystal will be given.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department


Description: A new diagnostic has been designed and commissioned that measures the profile of the beam in the halo channel of the Low Energy Demonstration Accelerator at the Los Alamos National Laboratory. This paper describes the algorithms written to analyze the data from that diagnostic, a combined wire scanner and halo scraper. These algorithms determine the safe insertions limit of the scrapers, spatially differentiate the scraper signal, amalgamate the wire scanner data with the differentiated scraper data, determine when both the core and combined distributions rise above the noise floor, and compute the moments of the combined distribution. Results of applying the algorithms to data acquired during experiments matching the beam into the halo channel are presented.
Date: May 1, 2001
Partner: UNT Libraries Government Documents Department


Description: In this paper we review the present picture of km halo in proton linacs. Space-charge forces acting in mismatched beams have been identified as a major cause of beam-halo. We present a definition of halo based on a ratio of moments of the distribution of the beam coordinates. We find from our initial studies that for halo detined in this way, a beam can have rms emittance growth without halo growth, but halo growth is always accompanied by rms emittance growth. We describe the beam-halo experiment that is in preparation at Los Alamos, which will address questions about the beam profiles, maximum particle amplitudes, and rms emittance growth associated with the halo.
Date: August 1, 2000
Partner: UNT Libraries Government Documents Department


Description: Four ionization beam profile monitors (IPM's) are in RHIC to measure vertical and horizontal profiles in the two rings. Each IPM collects and measures the distribution of electrons in the beamline resulting from residual gas ionization during bunch passage. The IPM's performed well during the 1999 commissioning run and early in the 2000 run. However as the bunch intensity increased there was a beam-induced ringing that increased in amplitude until it saturated the amplifiers and made the IPM's unusable. Near the end of the run the cause of the ringing was found and one IPM was fixed. At the start of the 2001 run all four IPM have EM1 shielding installed.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

A high-precision cryogenically-cooled crystal monochromator for the APS diagnostics beamline

Description: A high-precision cryogenically-cooled crystal monochromator has been developed for the APS diagnostics beamline. The design permits simultaneous measurements of the particle beam size and divergence. It provides for a large rotation angle, {minus}15{degree} to 180{degree}, with a resolution of 0.0005{degree}. The roll angle of the crystal can be adjusted by up to {+-}3{degree} with a resolution of 0.0001{degree}. A vertical translational stage, with a stroke of {+-}25 mm and resolution of 8 {micro}m, is provided to enable using different parts of the same crystal or to retract the crystal from the beam path. The modular design will allow optimization of cooling schemes to minimize thermal distortions of the crystal under high heat loads.
Date: July 24, 2000
Creator: Rotela, E.; Yang, B.; Sharma, s. & Barcikowski, A.
Partner: UNT Libraries Government Documents Department

Multipass beam position, profile and polarization measurements using intense photon target

Description: The Compton scattering of a circularly polarized laser beam condensed by an optical resonator can be used for multipass measurement of beam profile, position, and polarization in CEBAF's 250-m-long linac straight sections. The position and profile of the beam will be measured with an accuracy of {approximately}10 {mu}m in about 200 seconds and beam polarization with 10% accuracy in 100 seconds when the lowest beam energy is 500 MeV and the beam current is 100 {mu}A. For higher energies the times for measurement are much less. The photon target is within an optical resonator having a quality factor of 50. The Nd:Yag 5 W CW laser photon beam at wavelength {lambda} = 0.532 nm will have a waist {omega}{sub o} {approximately}30 {mu}m and a Rayleigh range of about 10 mm. Scanning the electron beams in the linac sections by this photon beam at a crossing angle of 0.1 rad will send to a proportional detector installed after the spreader magnet scattered photons with energies sharply correlated with the energy of the electrons.
Date: May 1, 1994
Creator: Karabekov, I.P.; Neil, G.; Karabekian, S. & Musakhanian, V.
Partner: UNT Libraries Government Documents Department

Evaluation of round colliding beams for Tevatron

Description: This paper presents investigation of round beams for increasing the luminosity in colliders. The main idea of round beams is briefly discussed. Numerical simulations of round colliding beams for the Tevatron are much in favor of round beams, because they provide reduction of harmful impact of beam-beam forces on beam sizes particles diffusion and better stability with respect to errors and imperfections.
Date: June 11, 1997
Creator: Danilov, V.V.
Partner: UNT Libraries Government Documents Department

A low diffraction beam technique for scanning in the shallow ocean

Description: The Localized Wave pulse project has created the concept of highly localized, pulsed wave energy. We have confirmed, and developed the technique in a series of experimental and numerical tests. This technique generates radiation, mechanical or electromagnetic, from an array. LW generation sends a broad frequency bandwidth pulse of energy along the array axis. The pulse has no sidelobes and maintains the frequency bandwidth and pulse amplitude better than any other method proposed to date. Confirmation of the theory by acoustic experiments show that the effect is real, and that the advantages of the technique can be realized in a laboratory environment. Numerical studies have shown that this effect is extendible to the microwave (vector field) and elastodynamic (tensor field) regimes as well as the stratified ocean environment. The main features of the LW beam are (1) the pulses are broad bandwidth and maintain that bandwidth over their entire working range; (2) the beam generates no side lobes; (3) the LW effect is accomplished in the linear regime, so that small errors in beam generation result in a less effective beam not the loss of the effect; and (4) the beam can be generated using present technology in the acoustic realm. The LW beam has a wide range of applications. As an active source, it offers a unique method of variable beam forming from spatially wide to the narrowest possible beam. Its uses include oceanographic sound velocity profile estimation and attenuation measurements. Since the pulse characteristics are changeable through the source signal parameters, it also offers the possibility of adaptive beam forming in real time. Passively, the LW array can use a wide spatial width listening pattern until something of interest occurs. Instantaneously, the listening pattern could be changed to a very narrow, steerable beam with a broad bandwidth. These ...
Date: December 1, 1994
Creator: Lewis, D.K.
Partner: UNT Libraries Government Documents Department

Multivideo image processing for beam profile monitoring system

Description: Some experiments at Jefferson Lab demand tight beam size ({approx} 100 {mu}m) and very low energy spread (< 5 x 10{sup {minus}5}). These experiments also require simultaneous and continuous monitoring of these quantities. This paper focuses on the development of the image processing aspects of the beam profile monitoring system. A pipelined image processor, Datacube's MaxVideo MV200, calculates beam sizes and positions from two beam profile monitors simultaneously at 10 Hz rate. Multiplexing software in the EPICS environment allows a single digitizer to process several input channels at high speed. This system makes the profile monitors usable for tuning the accelerator, as well as delivering critical information to the end stations. This paper discusses the issues related to the daily operational use of the system. The availability and reliability of the monitoring system became acceptable only after the implementation of programs that automatically setup and periodically check the monitors and digitizer. The system permits additional video channels without significant additional hardware cost.
Date: May 1, 2000
Creator: Hardy, D.; Chevstov, P.; Denard, J-C. & Dickson, R.
Partner: UNT Libraries Government Documents Department

Bunched beam echos in the AGS

Description: Beam echos have been measured at FNAL and CERN in coasting beams. A coherent oscillation introduced by a short RF burst decoheres quickly, but a coherent echo of this oscillation can be observed if the decohered oscillation is bounced off a second RF burst. In this report the authors describe first longitudinal echo measurements of bunched beam in the AGS accelerator. They applied a method proposed by Stupakov for transverse beam echos, where the initial oscillation is produced by a dipole kick and is bounced off a quadrupole kick. In the longitudinal case the dipole and quadrupole kicks are produced by cavities operating at a 90 and 0{degree} phase shift, respectively.
Date: August 1, 1998
Creator: Kewisch, J. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department