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A regulated magnetron pulser

Description: This paper describes and analysis of a 4.5-kV, 500-mA, regulated current pulser used to drive a Hitachi ZM130 magnetron in a particle-accelerator injector. In this application, precise beam from the injector. A high-voltage triode vacuum tube with active feedback is used to control the magnetron current. Current regulation and accuracy is better than 1%. The pulse width may be varied from as little as 5 {mu}m to cw by varying the width of a gate pulse. The current level can be programmed between 10 and 500 mA. Design of the pulser including circuit simulations, power calculations, and high-voltage issues are discussed.
Date: September 1, 1997
Creator: Rose, C.R.
Partner: UNT Libraries Government Documents Department

Four Pulse Drive System for the Beam Induction Cells for DARHT Axis 2

Description: The proposed drive system allows for the generation of up to four (4) high-quality radiographic pulses along one line-of-sight, having arbitrary pulse spacing ({approximately}500 ns), using demonstrated technologies. This concept uses a four-pulse drive system to drive both a 16-MeV ensemble of 250-kV, 4-kA induction cells and a four-pulse, 4-MeV injector. The key to this approach lies in the method used to combine four pulses from different generators in a manner that does not compromise the voltage flatness requirement of {+-} 1%. The induction cells use core material for only a single pulse. A simple reverse bias circuit is used to reset the cores between pulses, and the insulator has been redesigned to withstand the reverse reset voltage. This approach can be installed in stages so that the facility can be used for dual axis radiography while implementing the multi-pulsing capability. A dual double-pulse format has been identified which provides a sequence of two pulses along one line-of-sight within a 2-{micro}sec window. The 2-{micro}sec windows can be separated by arbitrary time intervals of 2- to 10-{micro}sec.
Date: June 28, 1999
Creator: Downing, J.; Carlson, R.; Melton, J. & Fockler, J.
Partner: UNT Libraries Government Documents Department

A review of high beam current RFQ accelerators and funnels

Description: The authors review the design features of several high-current (> 20-mA) and high-power (> 1-mA average) proton or H{sup {minus}} injectors, RFQs, and funnels. They include a summary of observed performance and will mention a sampling of new designs, including the proposed incorporation of beam choppers. Different programs and organizations have chosen to build the RFQ in diverse configurations. Although the majority of RFQs are either low-current or very low duty-factor, several versions have included high-current and/or high-power designs for either protons or H{sup {minus}} ions. The challenges of cooling, handling high space-charge forces, and coupling with injectors and subsequent accelerators are significant. In all instances, beam tests were a valuable learning experience, because not always did these as-built structures perform exactly as predicted by the earlier design codes. They summarize the key operational parameters, indicate what was achieved, and highlight what was learned in these tests. Based on this generally good performance and high promise, even more challenging designs are being considered for new applications that include even higher powers, beam funnels and choppers.
Date: December 1, 1998
Creator: Schneider, J.D.
Partner: UNT Libraries Government Documents Department

Los Alamos Neutron Science Center (LANSCE) accelerator timing system upgrade

Description: The Los Alamos Neutron Science Center (LANSCE) 800 MeV proton linear accelerator (linac) operates at a maximum repetition rate of twice the AC power line frequency, i.e. 120 Hz. The start of each machine cycle occurs a fixed delay after each zero-crossing of the AC line voltage. Fluctuations in the AC line frequency and phase are therefore present on all linac timing signals. Proper beam acceleration along the linac requires that the timing signals remain well synchronized to the AC line. For neutron chopper spectrometers, e.g., PHAROS at the Manuel Lujan Jr. Neutron Scattering Center, accurate neutron energy selection requires that precise synchronization be maintained between the beam-on-target arrival time and the neutron chopper rotor position. This is most easily accomplished when the chopper is synchronized to a stable, fixed frequency signal. A new zero-crossing circuit which employs a Phase-Locked Loop (PLL) has been developed to increase the phase and frequency stability of the linac timing signals and thereby improve neutron chopper performance while simultaneously maintaining proper linac operation. Results of timing signal data analysis and modeling and a description of the PLL circuit are presented.
Date: October 1, 1997
Creator: Rybarcyk, L.J. & Shelley, F.E. Jr.
Partner: UNT Libraries Government Documents Department

Beam chopper For the Low-Energy Undulator Test Line (LEUTL) in the APS

Description: The low-energy undulator test line (LEUTL) is being built and will be tested with a short beam pulse from an rf gun in the Advanced Photon Source (APS) at the Argonne National Laboratory. In the LEUTL a beam chopper is used after the rf gun to deflect the unwanted beam to a beam dump. The beam chopper consists of a permanent magnet and an electric deflector that can compensate for the magnetic deflection. A 30-kV pulsed power supply is used for the electric deflector. The chopper subsystem was assembled and tested for beamline installation. The electrical and beam properties of the chopper assembly are presented.
Date: August 1, 1997
Creator: Kang, Y.; Wang, J.; Milton, S. & Teng, L.
Partner: UNT Libraries Government Documents Department

Compensation of RF-Induced Energy Spread in the CEBAF Injector Chopping System

Description: The CEBAF injector chopping system must generate three interleaved 499 MHz pulse trains of independently variable current from a DC input beam prior to axial compression. The chopper consists of two deflection cavities with an aperture midway between them. Lenses flanking the aperture focus the beam from the first cavity into the center of the second, where the RF deflection from the first cavity is removed. The symmetry of the RF energy spread across any time-slice of the beam is dominantly odd. The inverting optics used to focus the beam into the second cavity causes near cancellation of the energy spread from the two cavities. We present experimental measurements of the energy spread effects from a fundamental frequency (1497 MHz) chopper prototype producing a beam of suitable transverse emittance and energy spread, and discuss the expected performance of the subharmonic chopper system to be used for commissioning starting in January 1994.
Date: May 1, 1993
Creator: Tiefenback, M.G. & Krafft, G.A.
Partner: UNT Libraries Government Documents Department

Beam sweeping system

Description: This article describes a system for rapidly sweeping a high-energy particle beam in a circular path on a target. The sweeping system deflects the beam in a single-turn rotating-field magnet that combines deflection in both planes into a single unit. The magnet current is up to 10 kA in amplitude and the sweep time is 1.6 {micro}s. The magnet consists of 4 conductors twisted to provide a uniform line-integral deflecting magnetic field, arranged inside a pressed-powder magnetic core. The pulsed power supply provides the current to the high radiation area of the target vault through several meters of stripline and coaxial cable by means of a magnetic pulse compression circuit based on saturing Ni-Fe and Metglas tape cores. At the Fermilab Antiproton Source increase proton beam intensities incident on the antiproton production target threaten to deliver energy densities sufficient to locally melt the target in a single pulse. The purpose of the sweep magnet is to spread the hot spot on the target with a sweep radius of up to 0.5 mm, greatly reducing the peak energy deposition.
Date: August 8, 2000
Creator: al., F.M. Bieniosek et
Partner: UNT Libraries Government Documents Department


Description: A new current structure for the fast traveling-wave 2.5-MeV beam chopper in the front end of the Spallation Neutron Source (SNS) has been suggested in [1]. The structure is based on the meander-folded notched stripline with dielectric supports and separators. Its design has been optimized using electromagnetic 3-D modeling with the MAFIA code package to provide rise and fall times in the range of 1 to 2 ns. A full-length (50 cm) prototype has been manufactured, and its preliminary measurements showed a good agreement with the calculations. Detailed measurements results and their comparison with simulations are presented. The latest front-end design requires a shorter, 35-cm chopper with a higher pulse voltage. Its meander-line current structure, based on the same principles, has also been optimized with MAFIA.
Date: October 1, 2000
Creator: KURRENOY, S. & POWER, J.
Partner: UNT Libraries Government Documents Department

Results of LEBT/MEBT reconfiguration at BNL 200 MeV LINAC

Description: The low energy (35 keV) and medium energy (750 keV) transport lines for both polarized and unpolarized H{sup -} have been reconfigured to reduce the beam emittance and beam losses out of the 200 MeV Linac. The medium energy line in the original layout was 7 m long, and had ten quadrupoles, two beam choppers, and three bunchers. The bunchers were necessary to keep the beam bunched at the entrance of the Linac. About 35% beam loss occurred, and the emittance growth was several fold. In the new layout, the 750 keV line is only 0.7 m long, with three quads and one buncher. We will present the experimental result of the upgrade.
Date: May 4, 2009
Creator: Raparia,D.; Alessi, J.; Briscoe, B.; Fite, J.; Gould, O.; Kponou, A. et al.
Partner: UNT Libraries Government Documents Department


Description: The DUV-FEL facility has been in operation in High Gain Harmonic Generation (HGHG) mode for one year producing 266 nm output from 177 MeV electrons. In this paper we present preliminary results of the Chirped Pulse Amplification (CPA) of HGHG radiation. In the normal HGHG process, a 1 ps electron beam is seeded by chirped 9 ps long 800 nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.
Date: September 8, 2003
Creator: DOYURAN,A. ET AL.
Partner: UNT Libraries Government Documents Department

Single-bunch synchrotron shutter

Description: An apparatus for selecting a single synchrotron pulse from the millions of pulses provided per second from a synchrotron source includes a rotating spindle located in the path of the synchrotron pulses. The spindle has multiple faces of a highly reflective surface, and having a frequency of rotation f. A shutter is spaced from the spindle by a radius r, and has an open position and a closed position. The pulses from the synchrotron are reflected off the spindle to the shutter such that the speed s of the pulses at the shutter is governed by: s=4 {times} {pi} {times} r {times} such that a single pulse is selected for transmission through an open position of the shutter.
Date: December 31, 1991
Creator: Norris, J.R.; Tang, Jau-Huei; Chen, Lin & Thurnauer, M.
Partner: UNT Libraries Government Documents Department

A study of beam chopping options for the ATLAS Positive Ion Linac

Description: Unbunched beam components from the injection beam bunching system must be removed prior to acceleration in the ATLAS Positive Ion Injector Linac (PII). A sine wave chopper has been used for this purpose up to now. Such a device can have a significant detrimental effect on the longitudinal and transverse beam emittance of heavy-ion beams which can be sufficiently severe to limit the overall beam quality from the ATLAS accelerator. A study of the optimum chopper configuration and chopper type was undertaken as part of a new ion source project for ATLAS. A transmission line chopper and a two harmonic chopper were investigated as alternatives to the conventional sine wave chopper. This paper reports the results of that investigation and discusses the design of the selected transmission line chopper.
Date: October 1, 1996
Creator: Pardo, R.C.; Bogaty, J.M. & Clifft, B.E.
Partner: UNT Libraries Government Documents Department

Development of a fast traveling-wave beam chopper for the SNS project

Description: High current and stringent restrictions on beam losses, below 1 nA/m, in the designed linac for the Spallation Neutron Source (SNS) require clean and fast--with the rise time from 2% to 98% less than 2.5 ns--beam chopping in its front end, at the beam energy 2.5 MeV. The development of new traveling-wave deflecting current structures based on meander lines is discussed. Three-dimensional time-domain computer simulations with MAFIA are used to study transient effects in the chopper and to optimize current structure design. Two options for the fast pulsed voltage generator--based on FETs and vacuum tubes--are considered, and their advantages and shortcomings for the SNS chopper are discussed.
Date: December 31, 1998
Creator: Kurennoy, S.S. & Power, J.F.
Partner: UNT Libraries Government Documents Department

Coherent Smith-Purcell radiation as a diagnostic for sub-picosecond electron bunch length

Description: We suggest a novel technique of measuring sub-picosecond electron bunch length base on coherent Smith-Purcell radiation (SPR) emitted when electrons pass close to the surface of a metal grating. With electron bunch lengths comparable to the grating period, we predict that coherent SPR will be emitted at large angles with respect to direction of beam propagation. As the bunch length shortens, the coherent SPR will be enhanced over the incoherent component that is normally observed at small angles. Furthermore, the angular distribution of the coherent SPR will be shifted toward smaller angles as the bunch length becomes much smaller than the grating period. By measuring the angular distribution of the coherent SPR, one can determine the bunch length of sub-picosecond electron pulses. This new technique is easy to implement and appears capable of measuring femtosecond electron bunch lengths.
Date: October 1, 1996
Creator: Nguyen, D.C.
Partner: UNT Libraries Government Documents Department


Description: The AGS Slow Extracted Beam (SEB) must be chopped with 250 ps bursts every 40 ns to permit time-of-flight (ToF) measurement of the secondary K{sup 0} beam. Standard techniques to produce this level of bunching would require excessive rf voltage, thus we have developed a ''Micro-Bunching'' technique of extracting the beam as it is forced between empty rf buckets. A specification of the required rf system will be given. Four-dimensional model simulations of particle dynamics for the planned rf and extraction systems will be shown. Simulations of previous tests along with the test measurements are also presented. Measurement of tight bunching requires dedicated instrumentation. The design of a detector system to measure bunch widths and the extinction factor between bunches will be given; considerations include the various particles produced and transported, timing precision and background.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Development of a fast traveling-wave beam chopper for the National Spallation Neutron Source

Description: High current and severe restrictions on beam losses, below 1 nA/m, in the designed linac for the National Spallation Neutron Source (NSNS) require clean and fast--with the rise time from 2% to 98% less than 2.5 ns to accommodate a 402.5-MHz beam structure--beam chopping in its front end, at the beam energy 2.5 MeV. The R and D program includes both modification of the existing LANSCE coax-plate chopper to reduce parasitic coupling between adjacent plates, and development of new traveling-wave deflecting structures, in particular, based on a meander line. Using analytical methods and three-dimensional time-domain computer simulations the authors study transient effects in such structures to choose an optimal chopper design.
Date: October 1, 1997
Creator: Kurennoy, S.S.; Jason, A.J.; Krawczyk, F.L. & Power, J.
Partner: UNT Libraries Government Documents Department

First tests of a traveling-wave chopper for the ATLAS positive ion linac.

Description: A ten segment traveling-wave chopper has been constructed and successfully tested at 5% of the design 12 MHz repetition rate. The chopper must remove unbunched tails from a partially bunched heavy-ion beam in order to avoid undue emittance growth in the linac and the production of undesirable satellite beam bunches. When poorly bunched beams traverse the traditional sine-wave chopper, it produces unacceptable transverse emittance growth and unnecessary beam loss. These effects are expected to be much reduced in the traveling wave chopper. First tests have confirmed the validity of these claims, clearly showing much reduced transverse emittance growth as compared to the original sine wave chopper and excellent selectivity for the desired beam. Details of these tests will be presented and compared to calculations. Operation of the new chopper at the full 12 MHz rate is the next goal. Development of a driver power supply capable of full CW operation will also be described.
Date: November 18, 1998
Creator: Pardo, R. C.
Partner: UNT Libraries Government Documents Department

Design and test of a beam transformer as a chopper

Description: This paper introduces a new type of chopper, which is similar to a beam transformer first discussed by R. Wideroe[1]. It is based on the fact that the RFQ has a rather small energy window. A pulsed beam transformer that provides 10% energy modulation to the beam in front of an RFQ can effectively chop the beam. It has fast rise- and fall-time and a short physical length. A prototype, which consists of a cavity and a high voltage pulsed power supply, has been constructed and tested. Two types of magnetic materials were tried for making the core of the cavity--the Finemet and the ferrite Philips 4M2. While the former gave good performance, the latter failed the test. Results from the bench measurements and a plan for beam tests are briefly described. For details the readers are referred to Ref. [2].
Date: September 2, 1999
Creator: W. Chou, Y. Mori, M. Muto, Y. Shirakabe and A. Takagi
Partner: UNT Libraries Government Documents Department

Design of a relativistic klystron two-beam accelerator prototype

Description: We are designing an experiment to study physics, engineering, and costing issues of an extended Relativistic Klystron Two-Beam Accelerator (RK-TBA). The experiment is a prototype for an RK-TBA based microwave power source suitable for driving a 1 TeV linear collider. Major components of the experiment include a 2.5-MV, 1.5-kA electron source, a 11.4-GHz modulator, a bunch compressor, and a 8-m extraction section. The extraction section will be comprised of 4 traveling-wave output structures, each generating about 360 MW of rf power. Induction cells will be used in the extraction section to maintain the average beam energy at 5 MeV. Status of the design is presented.
Date: October 1, 1995
Creator: Westenskow, G.; Caporaso, G. & Chen, Y.
Partner: UNT Libraries Government Documents Department

CW RF system of the Project-X accelerator front end

Description: Front end of a CW linac of the Project X contains an H{sup -} source, an RFQ, a medium energy transport line with the beam chopper, and a SC low-beta linac that accelerates H{sup -} from 2.5 MeV to 160 MeV. SC Single Spoke Resonators (SSR) will be used in the linac, because Fermilab already successfully developed and tested a SSR for beta = 0.21. Two manufactured cavities achieve 2.5 times more than design accelerating gradients. One of these cavities completely dressed, e.g. welded to helium vessel with integrated slow and fast tuners, and tested in CW regime. Successful tests of beta = 0.21 SSR give us a confidence to use this type of cavity for low beta (0.117) and for high-beta (0.4) as well. Both types of these cavities are under development. In present report the basic constrains, parameters, electromagnetic and mechanical design for all the three SSR cavities, and first test results of beta = 0.21 SSR are presented.
Date: September 1, 2010
Creator: Khabiboulline, T.; Barbanotti, S.; Gonin, I.; Solyak, N.; Terechkine, I.; Yakovlev, V. et al.
Partner: UNT Libraries Government Documents Department


Description: Two beam choppers were constructed which produce an approximately square, 20-ns pulse of 3+-MeV electrons out of the best portion of the 300-ns Astron beam or an 8-{micro}s microwave electron linac beam for injection into the electron-ring accelerator (ERA) compressor. The choppers are impedance-matched traveling-wave devices which deflect the beam with equal strength electric and magnetic forces, and are powered with either three-electrode spark gaps or thyratrons and a 20-ns pulse line. The electron beam is biased out of the beam-transport system with a dc magnetic field, and switched into it with the chopper.
Date: February 7, 1969
Creator: Faltens, Andris & Kerns, Cordon.
Partner: UNT Libraries Government Documents Department

The AGS New Fast Extracted Beam System orbit bump pulser

Description: The AGS New Fast Extracted Beam System (New FEB) is designed for RHIC injection and the g-2 experiment, performing single bunch multiple extraction at the prf of 20 to 100 Hz up to 12 times per AGS cycle. Capacitor-discharge pulsers are required to produce local orbit bumps at the fast kicker and ejector magnet locations. These pulsers have to deliver half-sine current pulses at 1 KA peak with a base width of 5 msec. The discharge voltage will require approximately 800V with a {plus_minus}0.1% accuracy. Direct charging will require a charger too costly and difficult to build because of the high prf. An alternative charging system is being developed to take advantage of the 1.5 sec idle time between each group of pulses. The charger power supply ratings and regulation requirements are thus greatly reduced. The system analysis and results from a prototype will be presented.
Date: June 1993
Creator: Chang, J. S. & Soukas, A. V.
Partner: UNT Libraries Government Documents Department

Simultaneous cancellation of beam emittance and energy spread in the CEBAF nuclear physics injector chopping system

Description: The CEBAF nuclear physics injector will utilize a unique chopping system consisting of two identical square box RF cavities with an inverting lens and a chopper aperture in-between. This system produces three interleaved 499 MHz cw electron beams from a 100 kV input beam. In this paper, we present our theoretical and numerical studies on how both emittance and energy spread are cancelled simultaneously in the dechopping process in the second cavity.
Date: June 1, 1993
Creator: Liu, H. & Bisognano, J.
Partner: UNT Libraries Government Documents Department

Design and preliminary results for a fast bipolar resonant discharge pulser using SCR switches for driving the injection bump magnets at the ALS

Description: A fast (4.0 us half period) resonant discharge pulser using SCRs has been designed and constructed to drive the injection bump magnet system at the Advanced Light Source (ALS). The pulser employs a series-parallel arrangement of Silicon Controlled Rectifiers (SCRS) that creates a bipolar high voltage ({plus_minus}10 KV), high peak current (6600 amps.) and a high di/dt (6000 amp/us) switch network that discharges a capacitor bank into the magnet load. Fast recovery diodes in series with the SCRs significantly reduces the SCR turn-off time during the negative current cycle of the magnet. The SCR switch provides a very reliable and stable alternative to the gas filled Thyratron. A very low impedance transmission system allows the pulser system to reside completely outside the storage ring shielding wall.
Date: May 1, 1993
Creator: Stover, G. & Reginato, L.
Partner: UNT Libraries Government Documents Department