100 Matching Results

Search Results

Advanced search parameters have been applied.

Beam parameters of a possible emittance-dynamics test area for NLC studies at the SLC

Description: A group at SLAC has studied the possibility of using the Stanford Linear Collider (SLC) to generate short-bunch small-emittance beams similar to those required for the Next Linear Collider (NLC). The conclusion is that such beams are feasible and that an experimental area for testing many concepts related to NLC beams can be provided with a reasonable addition of hardware to the existing SLC Linac. Some of the concepts that can be tested are: (1) effect tolerances of double bunch length compression, (2) wakefields of ultra-short bunches in accelerating structures, (3) the acceleration of short intense multiple bunches, (4) the generation and preservation of bunches with 100 to 1 emittances ratios, (5) beam deflections by collimators, (6) energy and energy spread control of multiple short bunches, and (7) vibration effects and trajectory stability for low emittance beams.
Date: August 1, 1992
Creator: Seeman, J. T.; Fieguth, T.; Kheifets, S.; Raubenheimer, T. & Yeremian, A. D.
Partner: UNT Libraries Government Documents Department

Over-compression, a method to shape the longitudinal bunch distribution for a reduced energy spread

Description: In the Stanford Linear Collider the energy spread of the bunches at the end of the linac is dominated by longitudinal wakefields. A short, high current bunch with a Gaussian shape will produce a double-horned energy distribution. It can be shown that certain charge distributions with a sharp rise time (about rectangular or half-Gaussian) will give no additional energy spread due to the linac, since the generated wakefield and the rf-curvature cancel each other exactly. In this paper different methods are presented on how to achieve such distributions by using non-linear dependences in the RTL (Ring-To-Linac) compression region. A simple and effective method to achieve such a distribution is by over-compression. When not fully compressing the bunch, there are two settings of the compressor voltage, under and over-compression, which give the same core bunch length in the linac. By switching from the under to the over-compressed setting, the tails are reduced from more than Gaussian to less than Gaussian beam tails. This results in a roughly rectangular shape which will give the wakefield-rf cancellation. Simulations, measurements and their implications are discussed.
Date: July 1, 1994
Creator: Decker, F. J.; Holtzapple, R. & Raubenheimer, T.
Partner: UNT Libraries Government Documents Department

Linac Coherent Light Source (LCLS) at 2--4 nm using the SLAC linac

Description: The authors describe the possible use of the SLAC linac to drive a unique, powerful, short wavelength Linac Coherent Light Source (LCLS). Using the FEL principle, lasing is achieved in a single pass of a high peak current electron beam through a long undulator by self-amplified-spontaneous-emission (SASE). The main components are a high-brightness electron RF gun with a photocathode, two electron bunch length compressors, the existing SLAC linac, beam diagnostics, and a long undulator combined with a FODO quadrupole focusing system. The RF gun, to be installed about 1 km from the end of the SLAC linac, would produce a single bunch of 6 x 10{sup 9} electrons with an invariant emittance of about 3 mm-mrad and a bunch length of about 500 {mu}m. That bunch is then accelerated to 100 MeV and compressed to a length of about 200 {mu}m. The main SLAC linac accelerates the bunch to 2 GeV were a second bunch compressor reduces the length to 30--40 {mu}m and produces a peak current of 2--3 kA. The bunch is then accelerated to 7--8 GeV and transported to a 50--70 m long undulator. Using electrons below 8 GeV, the undulator could operate at wavelengths down to 2 nm, producing about 10 GW peak power in sub-ps light pulses. At a linac repetition rate of 120 Hz, the average power is about 1 W. Linac operation at lower beam energies provides longer wavelength radiation. After the undulator, the beam is deposited in a dump. The LCLS light pulses are then distributed to multiple user stations using grazing incident mirrors. Length compression, emittance control, phase stability, FEL design criteria, and parameter tolerances are discussed. A demonstration experiment is also described which uses the SLAC linac and (possibly) the PALADIN undulator to study SASE to power saturation at wavelengths of ...
Date: August 1, 1993
Creator: Seeman, J. T.; Bane, K.; Boyce, R.; Loew, G.; Morton, P.; Nuhn, H. D. et al.
Partner: UNT Libraries Government Documents Department

The generation and acceleration of low emittance flat beams for future linear colliders

Description: Many future linear collider designs call for electron and positron beams with normalized rms horizontal and vertical emittances of {gamma}{epsilon}{sub x} = 3{times}10{sup {minus}6} m-rad and {gamma}{epsilon}{sub y} = 3{times}10{sup {minus}8} m-rad; these are a factor of 10 to 100 below those observed in the Stanford Linear Collider. In this dissertation, we examine the feasibility of achieving beams with these very small vertical emittances. We examine the limitations encountered during both the generation and the subsequent acceleration of such low emittance beams. We consider collective limitations, such as wakefields, space charge effects, scattering processes, and ion trapping; and also how intensity limitations, such as anomalous dispersion, betatron coupling, and pulse-to-pulse beam jitter. In general, the minimum emittance in both the generation and the acceleration stages is limited by the transverse misalignments of the accelerator components. We describe a few techniques of correcting the effect of these errors, thereby easing the alignment tolerances by over an order of magnitude. Finally, we also calculate ``fundamental`` limitations on the minimum vertical emittance; these do not constrain the current designs but may prove important in the future.
Date: November 1, 1991
Creator: Raubenheimer, T. O.
Partner: UNT Libraries Government Documents Department

Betatron phase advance measurement at SPEAR

Description: There are many reasons to determine the betatron phase advance between two azimuthal positions in a circular accelerator or storage ring. We have measured the betatron phase advance between various pairs of azimuthal points in the SPEAR Storage Ring by two different methods. The first method is to excite a steady state coherent betatron oscillation with a network analyzer. The second method is to excite a free coherent betatron oscillation with an impulse kick, and to digitally sample the transverse position of the beam at the pickup stations. The results of these digital samples are Fourier analyzed with a computer to obtain the phase advance. The second method is discussed, and the experimental results compared to theory.
Date: February 1, 1987
Creator: Morton, P.L.; Pellegrin, J.L.; Raubenheimer, T. & Ross, M.
Partner: UNT Libraries Government Documents Department

A new trajectory correction technique for linacs

Description: In this paper, we describe a new trajectory correction technique for high energy linear accelerators. Current correction techniques force the beam trajectory to follow misalignments of the Beam Position Monitors. Since the particle bunch has a finite energy spread and particles with different energies are deflected differently, this causes chromatic'' dilution of the transverse beam emittance. The algorithm, which we describe in this paper, reduces the chromatic error by minimizing the energy dependence of the trajectory. To test the method we compare the effectiveness of our algorithm with a standard correction technique in simulations on a design linac for a Next Linear Collider. The simulations indicate that chromatic dilution would be debilitating in a future linear collider because of the very small beam sizes required to achieve the necessary luminosity. Thus, we feel that this technique will prove essential for future linear colliders. 3 refs., 6 figs., 2 tabs.
Date: June 1, 1990
Creator: Raubenheimer, T.O. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Beam parameters of a possible emittance-dynamics test area for NLC studies at the SLC

Description: A group at SLAC has studied the possibility of using the Stanford Linear Collider (SLC) to generate short-bunch small-emittance beams similar to those required for the Next Linear Collider (NLC). The conclusion is that such beams are feasible and that an experimental area for testing many concepts related to NLC beams can be provided with a reasonable addition of hardware to the existing SLC Linac. Some of the concepts that can be tested are: (1) effect tolerances of double bunch length compression, (2) wakefields of ultra-short bunches in accelerating structures, (3) the acceleration of short intense multiple bunches, (4) the generation and preservation of bunches with 100 to 1 emittances ratios, (5) beam deflections by collimators, (6) energy and energy spread control of multiple short bunches, and (7) vibration effects and trajectory stability for low emittance beams.
Date: August 1, 1992
Creator: Seeman, J.T.; Fieguth, T.; Kheifets, S.; Raubenheimer, T. & Yeremian, A.D.
Partner: UNT Libraries Government Documents Department

Damping ring designs for a TeV Linear Collider

Description: In this paper we present a damping ring design for the TLC (TeV Linear Collider). The ring operates at 1.8 GeV. It has normalized emittances of elepsilon/sub x/ = 2.8 mrad and elepsilon/sub y/ = 25.4 nmrad. The damping times are /tau//sub x/ = 2.5 ms and /tau//sub y/ = 4.0 ms. To achieve these extremely low emittances and fast damping times, the ring contains 22 m of wigglers. 30 refs., 7 figs., 7 tabs.
Date: December 1, 1988
Creator: Raubenheimer, T.O.; Rivkin, L.Z. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Analytic estimates of coupling in damping rings

Description: In this paper we present analytic formulas to estimate the vertical emittance in weakly coupled electron/positron storage rings. We consider contributions from both the vertical dispersion and linear coupling of the betatron motions. In addition to simple expressions for random misalignments and rotations of the magnets, formulas are presented to calculate the vertical emittance blowup due to orbit distortions. The orbit distortions are assumed to be caused by random misalignments, but because the closed orbit is correlated from point to point, the effects must be treated differently. We consider only corrected orbits. Finally, the analytic expressions are compared with computer simulations of storage rings with random misalignments. 6 refs., 3 figs.
Date: March 1, 1989
Creator: Raubenheimer, T.O. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

A damping ring design for future linear colliders

Description: In this paper we present a preliminary design of a damping ring for the TeV Linear Collider (TLC), a future linear collider with an energy of 1/2 to 1 TeV in the center of mass. Because of limits on the emittance, repetition rate and longitudinal impedance, we use combined function FODO cells with wigglers in insertion regions; there are approximately 22 meters of wigglers in the 155 meter ring. The ring has a normalized horizontal emittance, including the effect of intrabeam scattering, which is less than 3 /times/ 10/sup /minus/6/ and an emittance ratio of epsilon/sub x/ approx. 100epsilon/sub y/. It is designed to damp bunches for 7 vertical damping times while operating at a repetition rate of 360 Hz. Because of these requirements on the emittance and the damping per bunch, the ring operates at 1.8 GeV and is relatively large, allowing more bunches to be damped at once. 10 refs., 5 figs., 2 tabs.
Date: March 1, 1989
Creator: Raubenheimer, T.O.; Gabella, W.E.; Morton, P.L.; Lee, M.J.; Rivkin, L.Z. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

A formalism and computer program for coupled lattices

Description: In this paper, a formalism to calculate the lattice functions and emittances of a coupled electron/positron storage ring is presented. The lattice functions are calculated directly from the modal matrix of the betatron transport matrix for the ring. The emittances and damping rates are then calculated from the invariants found in the diagonalized representation. In addition, a computer program is described which uses the formalism to calculate the coupled lattice functions, emittances and damping rates. The program can either reconstruct the closed orbit from BPM data and dipole corrector strengths, or construct an orbit from misalignments entered into the the lattice and then optionally correct the orbit with dipole correctors. The lattice functions, emittances, etc. are then calculated about the resulting closed orbit. 7 refs.
Date: April 1, 1989
Creator: Raubenheimer, T.O.
Partner: UNT Libraries Government Documents Department

A new method of correcting the trajectory in linacs

Description: This paper describes a new method of reducing the transverse emittance dilution in linear colliders due to both transverse wakefields and dispersive errors. The technique is a generalization of the Dispersion-Free correction algorithm; the dilutions are corrected locally by varying the beam trajectory. This technique complements BNS damping which primarily corrects the dilutions resulting from coherent betatron oscillations. Finally, the results of simulations are presented demonstrating the viability of the technique. 6 refs., 1 fig., 1 tab.
Date: May 1, 1991
Creator: Raubenheimer, T.O & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

The generation and acceleration of low emittance flat beams for future linear colliders

Description: Many future linear collider designs call for electron and positron beams with normalized rms horizontal and vertical emittances of {gamma}{epsilon}{sub x} = 3{times}10{sup {minus}6} m-rad and {gamma}{epsilon}{sub y} = 3{times}10{sup {minus}8} m-rad; these are a factor of 10 to 100 below those observed in the Stanford Linear Collider. In this dissertation, we examine the feasibility of achieving beams with these very small vertical emittances. We examine the limitations encountered during both the generation and the subsequent acceleration of such low emittance beams. We consider collective limitations, such as wakefields, space charge effects, scattering processes, and ion trapping; and also how intensity limitations, such as anomalous dispersion, betatron coupling, and pulse-to-pulse beam jitter. In general, the minimum emittance in both the generation and the acceleration stages is limited by the transverse misalignments of the accelerator components. We describe a few techniques of correcting the effect of these errors, thereby easing the alignment tolerances by over an order of magnitude. Finally, we also calculate fundamental'' limitations on the minimum vertical emittance; these do not constrain the current designs but may prove important in the future.
Date: November 1, 1991
Creator: Raubenheimer, T.O.
Partner: UNT Libraries Government Documents Department

Diagnostic for dynamic aperture

Description: In large accelerators and low beta colliding beam storage rings, the strong sextupoles, which are required to correct the chromatic effects, produce strong nonlinear forces which act on particles in the beam. In addition in large hadron storage rings the superconducting magnets have significant nonlinear fields. To understand the effects of these nonlinearities on the particle motion there is currently a large theoretical effort using both analytic techniques and computer tracking. This effort is focused on the determination of the 'dynamic aperture' (the stable acceptance) of both present and future accelerators and storage rings. A great deal of progress has been made in understanding nonlinear particle motion, but very little experimental verification of the theoretical results is available. In this paper we describe 'dynamic tracking', a method being studied at the SPEAR storage ring, which can be used to obtain experimental results which are in a convenient form to be compared with the theoretical predictions.
Date: April 1, 1985
Creator: Morton, P.L.; Pellegrin, J.L.; Raubenheimer, T.; Rivkin, L.; Ross, M.; Ruth, R.D. et al.
Partner: UNT Libraries Government Documents Department

Superconvergent tracking and invariant surfaces in phase space

Description: The question of long term beam stability in very large storage rings presents an extraordinary challenge in nonlinear dynamics. Since current computational methods seem less than adequate on the long time scales involved, we have undertaken a program of evaluating several methods that either are new or have not been tried in accelerator problems heretofore. The methods we investigate fall into two categories: (1) iteration of maps describing concatenated machine elements, for tracking of single particles, and (2) infinite-time methods for direct computation of invariant surfaces in phase space.
Date: April 1, 1985
Creator: Ruth, R.D.; Raubenheimer, T. & Warnock, R.L.
Partner: UNT Libraries Government Documents Department

Measured emittance versus store time in the SLC damping ring

Description: Emittance studies at the SLC North Damping Ring led to precise measurements of the damping time using three independent methods. These measurements were done at three different locations: (1) in the ring using a fast gated video camera which allows the acquisition of the image of the synchrotron light from a single turn, (2) using the extracted beam and a single wire scanner in the ring-to-linac transport line, and (3) in the linac using four wire scanners. In addition the extracted beam emittance was studied as a function of various parameters. A significant dependence on the tune was observed.
Date: March 1, 1992
Creator: Decker, F.J.; Emma, P.; Krejcik, P.; Limberg, T.; Minty, M.; Moshammer, H. et al.
Partner: UNT Libraries Government Documents Department

Calculations of emittance and damping time effects in the SLC damping rings

Description: In a recent NDR machine experiment the transverse emittance was studied as a function of store time and tune. To explain the observed transverse emittance damping time constants, the magnetic measurement data of the longitudinal field of the bending magnets had to be taken into account. The variation of the transverse emittances with tune due to misalignments and the associated anomalous dispersion is studied as well as the effect of synchrobetatron coupling due to dispersion in the RF cavities.
Date: March 1, 1992
Creator: Limberg, T.; Moshammer, H.; Raubenheimer, T.; Spencer, J. & Siemann, R.
Partner: UNT Libraries Government Documents Department

Experimental Measurements of the Secondary Electron Yield in the Experimental Measurement of the Secondary Electron Yield in the PEP-II Particle Accelerator Beam Line

Description: Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders (LC) such as ILC and CLIC. To test a series of promising possible electron cloud mitigation techniques as surface coatings and grooves, in the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed several test vacuum chambers including (i) a special chamber to monitor the variation of the secondary electron yield of technical surface materials and coatings under the effect of ion, electron and photon conditioning in situ in the beam line; (ii) chambers with grooves in a straight magnetic-free section; and (iii) coated chambers in a dedicated newly installed 4-magnet chicane to study mitigations in a magnetic field region. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the LC damping ring, focusing on the first experimental area and on results of the reduction of the secondary electron yield due to in situ conditioning.
Date: August 25, 2010
Creator: Pivi, M.T.F.; Collet, G.; King, F.; Kirby, R.E.; Markiewicz, T.; Raubenheimer, T.O. et al.
Partner: UNT Libraries Government Documents Department

First Demonstration of the Echo-Enabled Harmonic Generation Technique for Short-Wavelength Seeded Free Electron Lasers

Description: We report the first experimental demonstration of the echo-enabled harmonic generation (EEHG) technique which holds great promise for generation of high power, fully coherent short-wavelength radiation. In this experiment, coherent radiation at the 3rd and 4th harmonic of the second seed laser is generated from the so-called beam echo effect. The experiment confirms the physics behind this technique and paves the way for applying the EEHG technique for seeded x-ray free electron lasers.
Date: August 25, 2010
Creator: Xiang, D.; Colby, E.; Dunning, M.; Gilevich, S.; Hast, C.; Jobe, K. et al.
Partner: UNT Libraries Government Documents Department

Preliminary Results of the Echo-Seeding Experiment ECHO-7 at SLAC

Description: ECHO-7 is a proof-of-principle echo-enabled harmonic generation FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment aims to generate coherent radiation at 318 nm and 227 nm, which are the 5th and 7th harmonic of the infrared seed laser. In this paper we present the preliminary results from the commissioning run of the completed experimental setup which started in April 2010.
Date: June 15, 2010
Creator: Xiang, D.; Colby, E.; Ding, Y.; Dunning, M.; Frederico, J.; Gilevich, S. et al.
Partner: UNT Libraries Government Documents Department

Preliminary results of the echo-seeding experiment at SLAC

Description: ECHO-7 is a proof-of-principle echo-enabled harmonic generation FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment aims to generate coherent radiation at 318 nm and 227 nm, which are the 5th and 7th harmonic of the infrared seed laser. In this paper we present the preliminary results from the commissioning run of the completed experimental setup which started in April 2010.
Date: May 23, 2010
Creator: Xiang, D.; Colby, E.; Ding, Y.; Dunning, M.; Frederico, J.; Gilevich, S. et al.
Partner: UNT Libraries Government Documents Department

Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring

Description: The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.
Date: August 24, 2011
Creator: Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E. et al.
Partner: UNT Libraries Government Documents Department

Science and Technology of Future Light Sources

Description: Many of the important challenges facing humanity, including developing alternative sources of energy and improving health, are being addressed by advances that demand the improved understanding and control of matter. While the visualization, exploration, and manipulation of macroscopic matter have long been technological goals, scientific developments in the twentieth century have focused attention on understanding matter on the atomic scale through the underlying framework of quantum mechanics. Of special interest is matter that consists of natural or artificial nanoscale building blocks defined either by atomic structural arrangements or by electron or spin formations created by collective correlation effects. The essence of the challenge to the scientific community has been expressed in five grand challenges for directing matter and energy recently formulated by the Basic Energy Sciences Advisory Committee [1]. These challenges focus on increasing our understanding of, and ultimately control of, matter at the level of atoms, electrons. and spins, as illustrated in Figure 1.1, and serve the entire range of science from advanced materials to life sciences. Meeting these challenges will require new tools that extend our reach into regions of higher spatial, temporal, and energy resolution. X-rays with energies above 10 keV offer capabilities extending beyond the nanoworld shown in Figure 1.1 due to their ability to penetrate into optically opaque or thick objects. This opens the door to combining atomic level information from scattering studies with 3D information on longer length scales from real space imaging with a resolution approaching 1 nm. The investigation of multiple length scales is important in hierarchical structures, providing knowledge about function of living organisms, the atomistic origin of materials failure, the optimization of industrial synthesis, or the working of devices. Since the fundamental interaction that holds matter together is of electromagnetic origin, it is intuitively clear that electromagnetic radiation is the ...
Date: December 1, 2008
Creator: Dierker,S.; Bergmann, U.; Corlett, J.; Dierker, S.; Falcone, R.; Galayda, J. et al.
Partner: UNT Libraries Government Documents Department

Conceptual Design of the Drive Beam for a PWFA-LC

Description: Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for bunch with triangular shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective than the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed by the PWFA collaboration. Here we will describe the conceptual design and optimization of the drive beam, which includes the drive beam linac and distribution system. We apply experience of the CLIC drive beam design and demonstration in the CLIC Test Facility (CTF3) to this study. We discuss parameter optimization of the drive beam linac structure and evaluate the drive linac efficiency in terms of the drive beam distribution scheme and the klystron/modulator requirements.
Date: August 3, 2009
Creator: Pei, S.; Hogan, M.J.; Raubenheimer, T.O.; Seryi, A.; /SLAC; Braun, H.H. et al.
Partner: UNT Libraries Government Documents Department