434 Matching Results

Search Results

Advanced search parameters have been applied.

Phase and synchronous detector theory as applied to beam position and intensity measurements

Description: A popular signal processing technique for beam position measurements uses the principle of amplitude-to-phase (AM/PM) conversion and phase detection. This technique processes position-sensitive beam-image-current probe-signals into output signals that are proportional to the beam`s position. These same probe signals may be summed and processed in a different fashion to provide output signals that are proportional to the peak beam current which is typically referred to as beam intensity. This paper derives the transfer functions for the AM/PM beam position and peak beam current processors.
Date: May 1, 1995
Creator: Gilpatrick, J.D.
Partner: UNT Libraries Government Documents Department

Cumulative Beam Breakup with Random Displacement of Cavities and Focusing Elements

Description: We have recently developed an analytical formalism for cumulative beam breakup in linear accelerators with arbitrary beam current profile. The same formalism could be used to investigate the beam breakup-enhanced displacement due to the misalignment of the cavities and the focusing elements. In this paper this analytical formalism is extended and applied to investigate the behavior of beams in misaligned pulsed and cw linear accelerators.
Date: August 1, 2002
Creator: Delayen, Jean
Partner: UNT Libraries Government Documents Department

Intensity Limitations in Fermilab Main Injector

Description: The design beam intensity of the FNAL Main Injector (MI) is 3 x 10{sup 13} ppp. This paper investigates possible limitations in the intensity upgrade. These include the space charge, transition crossing, microwave instability, coupled bunch instability, resistive wall, beam loading (static and transient), rf power, aperture (physical and dynamic), coalescing, particle losses and radiation shielding, etc. It seems that to increase the intensity by a factor of two from the design value is straightforward. Even a factor of five is possible provided that the following measures are to be taken: an rf power upgrade, a {gamma}{sub t}-jump system, longitudinal and transverse feedback systems, rf feedback and feedforward, stopband corrections and local shieldings.
Date: June 1, 1997
Creator: Chan, W.
Partner: UNT Libraries Government Documents Department

Beam Effects from an Increase of LINAC Current from 40 ma to 49 Milliamperes

Description: On March 25, 2002 the FNAL Linac had been running at a decreased 40 ma of beam current for some time. Both the 400 MeV Linac and the 8GeV Booster had been tuned to optimum running during that time. Optimum running for the Booster was at 4.1e12 per pulse. Losses at injection and at transition were limiting intensity at the time. By March 26, 2002 the Linac beam current had been increased to 49 ma. The optimum Booster intensity immediately jumped to 4.5e12 per pulse and increased in the next few days to 4.8e12 and 5e12 per pulse. Booster was not retuned until early April when a low-loss 5.0e12 was obtained for stacking operations. Linac current had sagged to 47 ma by then. Measurements were made on the 25th at 40 ma and the 26th and 27th at 49 ma. This is a report and discussion of those measurements.
Date: June 5, 2002
Creator: Tomlin, Ray
Partner: UNT Libraries Government Documents Department

Beam profile analysis for the C{ampersand}MS B231 electron beam welding machines

Description: The electron beams produced by two different welders were examined using computer assisted tomographic (CT) analysis. The machines used are Hamilton Standard welders with 150 kV/50mA maximum. One machine uses a ribbon filament while the other uses a hairpin filament. The objective of this study was to characterize the beam power distribution on each machine to see if weld parameters could easily be transferred between machines. Beam focus, voltage, and current settings were pre-selected to duplicate the welding conditions used in LLNL program applications. The results show that the actual beam currents measured by Faraday cup are 5 to 10% higher for the first machine and 30% lower for the second. The CT analysis of the beam shapes shows that the hairpin filament welder produces an elliptical beam shape in the sharp focus condition that defocuses to a diamond shape. The ribbon filament welder produced less of an elliptical beam shape in the sharp focus condition, but when defocused, acquires an elliptical shape. CT analysis of the effects of defocus on the peak power density shows that the hairpin filament drops in peak power density much more quickly than the ribbon filament for a given amount of defocus. Furthermore, it was more difficult to find and repeat the sharp focus condition for the hairpin filament, particularly at higher beam currents.
Date: June 12, 1997
Creator: Elmer, J. W.; Teruya, A.T. & Gauthier, M.
Partner: UNT Libraries Government Documents Department

The development of beam current monitors in the APS

Description: The Advanced Photon Source (APS) is a third-generation 7-GeV synchrotron radiation source. The precision measurement of beam current is a challenging task in high energy accelerators, such as the APS, with a wide range of beam parameters and complicated noise, radiation, and thermal environments. The beam pulses in the APS injector and storage ring have charge ranging from 50pC to 25nC with pulse durations varying from 30ps to 30ns. A total of nine non- intercepting beam current monitors have been installed in the APS facility (excluding those in the linac) for general current measurement. In addition, several independent current monitors with specially designed redundant interlock electronics are installed for personnel safety and machine protection. This paper documents the design and development of current monitors in the APS,. discusses the commissioning experience in the past year, and presents the results of recent operations.
Date: July 1, 1995
Creator: Wang, X.; Lenkszus, F. & Rotela, E.
Partner: UNT Libraries Government Documents Department

Magnetic design and measurement of nonlinear multipole magnets for the APT beam expander system

Description: Two prototype nonlinear multipole magnets have been designed for use in the 800-MeV beam test of the APT beam-expansion concept at LANSCE. The iron-dominated magnets each consist of three independent coils, two for producing a predominantly octupole field with a tunable duodecapole component, and one for canceling the residual quadrupole field. Two such magnets, one for shaping each transverse plane, are required to produce a rectangular, uniform beam current density distribution with sharp edges on the APT target. This report will describe the magnetic design of these magnets, along with field measurements, and a comparison to the magnetic design.
Date: October 1, 1997
Creator: Barlow, D.B.; Shafer, R.E.; Martinez, R.P.; Walstrom, P.L.; Kahn, S.; Jain, A. et al.
Partner: UNT Libraries Government Documents Department

New initiatives for producing high current electron accelerators

Description: New classes of compact electron accelerators able to deliver multi-kiloamperes of pulsed 10-50 MeV electron beams are being studied. One class is based upon rf linac technology with dielectric-filled cavities. For materials with {epsilon}/{epsilon}{sub o}>>1, the greatly increased energy storage permits high current operation. The second type is a high energy injected betatron. Circulating current limits scale as {Beta}{sup 2}{gamma}{sup 3}.
Date: November 1, 1996
Creator: Faehl, R.J.; Keinigs, R.K. & Pogue, E.W.
Partner: UNT Libraries Government Documents Department

Klystron beam-bunching lecture

Description: Electron beam current modulation in a klystron is the key phenomenon that accounts for klystron gain and rf power generation. Current modulation results from the beams` interaction with the rf fields in a cavity, and in turn is responsible for driving modulation in the next rf cavity. To understand the impact of the current modulation in a klystron, we have to understand both the mechanism leading to the generation of the current modulation and the interaction of a current-modulated electron beam with an rf cavity. The cavity interaction is subtle, because the fields in the cavity modify the bunching of the beam within the cavity itself (usually very dramatically). We will establish the necessary formalism to understand klystron bunching phenomena which can be used to describe rf accelerator cavity/beam interactions. This formalism is strictly steady-state; no transient behavior will be considered. In particular, we will discuss the following: general description of klystron operation; beam harmonic current; how beam velocity modulation induced by an rf cavity leads to current modulation in both the ballistic and space-charge dominated regimes; use of Ramo`s theorem to define the power transfer between a bunched electron beam and the cavity; general cavity model with external coupling (including an external generator if needed), used to describe the input cavity, idler cavities, and the output cavity, including the definition of beam loaded-cavity impedance. Although all these are conceptually straight-forward, they represent a fair amount of physics, and to derive some elements of the formalism from first principles requires excessive steps. Our approach will be to present a self-consistent set of equations to provide a mechanism that leads to a quantifiable description of klystron behavior; derivations for moderately complex formulas will be outlined, and a relatively complex derivation of the self-consistent set of equations can be found in the ...
Date: October 1, 1996
Creator: Carlsten, B.
Partner: UNT Libraries Government Documents Department

Laser diagnostic for high current H{sup {minus}} beams

Description: Laser photodetachment can be used on high current, high energy H{sup {minus}} beams to carry out a wide variety of beam diagnostic measurements parasitically during normal operation, without having to operate the facility at either reduced current or duty cycle. Suitable Q-switched laser systems are small, inexpensive, and can be mounted on or near the beamline. Most of the proposed laser-based diagnostics techniques have already been demonstrated.
Date: January 1, 1998
Creator: Shafer, R.E.
Partner: UNT Libraries Government Documents Department

Suppression of the 1 MHz beam current modulation in the LEDA/CRITS proton source

Description: Earlier operation of a microwave proton source exhibited an approximate 1-MHz modulation in the beam current. This oscillation could cause instabilities at higher energies in the linac, as the low-level RF control for linac operation rolls off at 200 kHz. Tests on a dummy load show the modulation is created by the magnetron itself: at a typical power level required for the source operation (680W), the 1-MHz sideband level was as high as {minus}4 dB from carrier. Since the magnetron exhibited better behavior at higher levels, a RF power attenuator is inserted to force the magnetron to run at a 50% higher power level for the same final power in the load. This attenuator is made of two antennas plunged in the waveguide and connected to dummy loads by a coaxial line. As the antenna are separated by a quarter of the guided wavelength, mismatching effects approximately cancel each other. The antenna length is experimentally adjusted to obtain the {minus}1.8 dB attenuation required. Magnetron operation at the higher power level gives a beam current spectrum free of the 1-MHz modulation, showing the coherent beam noise is not generated by plasma chamber phenomena.
Date: December 1, 1998
Creator: Balleyguier, P.; Sherman, J. & Zaugg, T.
Partner: UNT Libraries Government Documents Department

Diagnostics for a 1.2 kA, 1 MeV electron induction injector

Description: We are constructing a 1.2-kA, 1-MeV, electron induction injector as part of the RTA program, a collaborative effort between LLNL and LBNL to develop relativistic klystrons for Two-Beam Accelerator applications. The RTA injector will also be used in the development of a high-gradient, low-emittance, electron source and beam diagnostics for the second axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) Facility. The electron source will be a 3.5``-diameter, thermionic, flat-surface, m-type cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 200 {pi}-mm-mr. Precise measurement of the beam parameters is required so that performance of the RTA injector can be confidently scaled to the 4-kA, 3-MeV, and 2-microsecond pulse parameters of the DARHT injector. Planned diagnostics include an isolated cathode with resistive divider for direct measurement of current emission, resistive wall and magnetic probe current monitors for measuring beam current and centroid position, capacitive probes for measuring A-K gap voltage, an energy spectrometer, and a pepper-pot emittance diagnostic. Details of the injector, beam line, and diagnostics are presented.
Date: May 11, 1998
Creator: Houck, T.L.; Anderson, D.E.; Eylon, S.; Henestroza, E.; Lidia, S.M.; Vanecek, D.L. et al.
Partner: UNT Libraries Government Documents Department

Results from a double Vlasov model for negative ion extraction from volume sources

Description: A new negative ion source-extraction model has been formulated and implemented which explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that: (1) for high-beam currents, the beam current is limited by a transverse space-charge limit, not an emission limit; (2) there is a saddle point with a concomitant potential barrier preventing most volume produced negative ions from being extracted (the combination of 1 and 2 indicates that in some interesting cases there is the opportunity to increase extraction currents above values presently observed); (3) introduction of cesium may cause an actual increase in the transverse space-charge limit by accumulation of positive ions of cesium in the presheath.
Date: July 1, 1998
Creator: Olsen, D.K.; Raridon, R.J. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Shipping and Alignment for the SNS Cryomodule

Description: The Spallation Neutron Source (SNS) requires 32 super conducting cryomodules to raise the beam energy of the accelerator to 1.3 GeV. Thomas Jefferson National Accelerator Facility (Jefferson Lab) has been contracted to build and deliver these cryomodules. The SNS cryomodules are being assembled and tested at Jefferson Lab in Newport News Virginia, and installed at the SNS facility in Oak Ridge, Tennessee. The cryomodules will be transported via a flatbed air ride trailer over the approximate 500-mile distance. This paper describes the alignment of the cavities and how it is preserved during the shipping and operation of the cryomodule. It includes a description of the support scheme developed to preserve the alignment during shipping and operation, and how the support scheme forms a very rigid structure with natural frequencies well above the expected 10 Hz driving frequencies. The entire cryomodule is supported by a dampened cradle, which is mounted directly onto the bed of the trailer. The transportation environment was evaluated by instrumenting a similar cryomodule with accelerometers during a road test of approximately 300 miles. A complete modal analysis of the whole system has been performed and the steps taken to minimize any transport-induced loading/deflections are discussed.
Date: June 1, 2001
Creator: Whitlatch, T.; Curtis, C.; Daly, E.; Matsumoto, K.; Mutton, P.; Pitts, J. et al.
Partner: UNT Libraries Government Documents Department

Scaling of Wakefield Effects in Recirculating Linacs

Description: Expressions for the induced energy spread and emittance degradation of a single bunch due to the longitudinal and transverse impedance of rf cavities at the end of a linac structure are presented. Scaling of the formulae with rf frequency is derived. Scaling of the threshold current for the multibunch, multipass beam breakup (BBU) instability in recirculating linacs with accelerator and beam parameters is also derived.
Date: June 1, 2001
Creator: Merminga, Lia; Neil, George R.; Yunn, Byung C. & Bisognano, Joseph J.
Partner: UNT Libraries Government Documents Department

Two Applications of Direct Digital Down Converters in Beam Diagnostics

Description: The technologies of direct digital down converters, digital frequency synthesis, and digital signal processing are being used in many commercial applications. Because of this commercialization, the component costs are being reduced to the point where they are economically viable for large scale accelerator applications. This paper will discuss two applications of these technologies to beam diagnostics. In the first application the combination of direct digital frequency synthesis and direct digital down converters are coupled with digital signal processor technology in order to maintain the stable gain environment required for a multi-electrode beam position monitoring system. This is done by injecting a CW reference signal into the electronics as part of the front-end circuitry. In the second application direct digital down converters are used to provide a novel approach to the measurement of beam intensity using cavity current monitors. In this system a pair of reference signals are injected into the cavity through an auxiliary port. The beam current is then calculated as the ratio of the beam signal divided by the average of the magnitude of the two reference signals.
Date: May 1, 2000
Creator: Powers, Tom; Flood, Roger; Hovater, Curt & Musson, John
Partner: UNT Libraries Government Documents Department

TiN coating of the PEP-II low-energy ring aluminum arc vacuum chambers

Description: The PEP-II Low-Energy Ring will operate at a nominal energy of 3.1 GeV with a positron beam current of 2.1 A. Design parameters for vacuum components are 3.5 GeV at 3 A. The arc vacuum system is based on an aluminum antechamber concept. It consists of 192 pairs of 2 m long magnet chambers and 5.5 m long pumping chambers. Titanium nitride coating of the entire positron duct is needed in order to suppress beam instabilities caused by multipactoring and the {open_quotes}electron-cloud{close_quotes} effect. An extensive R&D program has been conducted to develop coating parameters that give proper stoichiometry and a suitable thickness of TiN. The total secondary emission yield of TiN-coated aluminum coupons has been measured after the samples were exposed to air and again after electron-beam bombardment. A coating facility has been built to cope with the large quantity of production chambers and the very tight schedule requirements.
Date: May 1, 1997
Creator: Kennedy, K.; Harteneck, B. & Millos, G.
Partner: UNT Libraries Government Documents Department

High Current, Long Beam Pulse with SLED

Description: A proposed, high charge, fixed target experiment (E-158) is planned to run with the highest possible energies available at the Stanford Linear Accelerator Center (SLAC), at 45 and 48 Gev. The charge is up to 6 {center_dot} 10{sup 11} particles in a 370 ns long beam pulse. The SLAC Energy Development (SLED) rf system generates an increasing no-load beam energy, with a linearly decreasing slope. We show how to obtain a current variation that tracks the no-load voltage, resulting in zero energy spread. We discuss the results of a lower energy experiment that verifies the predicted charge and current at the energies required for E-158.
Date: April 16, 1999
Creator: Decker, Franz-Josef
Partner: UNT Libraries Government Documents Department

Operation of CEBAF with heavy beamloading

Description: CEBAF is a 4 GeV, 200 {micro}A five-pass recirculating superconducting electron accelerator that has been operating for nuclear physics research at full energy since November 95. The beam current has been increased to over 180 {micro}A at 4 GeV with the maximum current in the linac over 900 {micro}A. The superconducting cavities operate in a regime where the beam-induced voltage is comparable to the accelerating gradient. The operational limits and the issues required to maintain stable operation of the 1,497 MHz superconducting cavities will be discussed, together with the implications for the other accelerator systems. There are three experimental Halls which can run simultaneously with three interleaved 499 MHz bunch trains and RF separators. Operation with simultaneous beams to two Halls is now routine, and simultaneous three beam operation has been demonstrated. The maximum design current per bunch train (120 {micro}A) has been achieved. Hall B eventually requires beam currents as low as 1 nA (200 pA has been delivered) simultaneous with delivery of up to 200 {micro}A to the other Halls. The required beam current ratio of 10,000 has been achieved; development of 1 nA beam position monitors continues.
Date: July 1, 1997
Creator: Hutton, A.
Partner: UNT Libraries Government Documents Department

Advances in DC photocathode electron guns

Description: At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughout. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, the authors will review recent results and discuss implications for future photocathode guns.
Date: July 1, 1998
Creator: Dunham, Bruce M.; Heartmann, P.; Kazimi, Reza; Liu, Hongxiu; Poelker, B. M.; Price, J. S. et al.
Partner: UNT Libraries Government Documents Department