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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

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

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

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

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

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

Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

Description: GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun.
Date: April 1, 2011
Creator: J. Grames, R. Suleiman, P.A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M.L. Stutzman
Partner: UNT Libraries Government Documents Department


Description: Recent years have witnessed the development of accelerators of ever-larger current, both peak and average, as well as a proliferation of storage rings of ever-greater luminosity. Consequently, there is considerable interest in and growing concern with, the phenomena which limit beam currents and beam densities, namely, the collective modes of behavior of relativistic particle beams. Furthermore, it has been demonstrated that the collective behavior can be controlled, at least to some extent, turned to good advantage, and employed for collective acceleration in devices such as the electron ring accelerator. Quite naturally then, almost every accelerator conference during the last five years has had a review paper on collective effects, while at the same time the number of original papers in this area now exceeds many hundreds. And thus I am faced with the dilemma of being unable to give a comprehensive and complete review (such a review, incidentally, would be most valuable; in my judgment the time is ripe for a comprehensive monograph on the subject.), and yet finding it difficult, in a brief review, to be comprehensible, balanced, and yet fresh. I have resolved the dilemma by firstly supplying sufficient references as to allow the interested reader to readily approach and efficiently attack the literature. Secondly, I take a few steps away from the details and the realities of the field and with the advantage of the broader view so gained, describe the basic many-body physics underlying the subject. Thirdly, I present a few examples of collective behavior, in part to make the general remarks concrete, but in large measure in order to illustrate the beauty of this kind of physics. Finally, I make some remarks on methods for control of undesirable collective behavior, and on the present state of understanding of the field.
Date: September 1, 1972
Creator: Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Observation of Instabilities of Coherent Transverse Ocillations in the Fermilab Booster

Description: The Fermilab Booster - built more than 40 years ago - operates well above the design proton beam intensity of 4 {center_dot} 10{sup 12} ppp. Still, the Fermilab neutrino experiments call for even higher intensity exceeding 5.5 {center_dot} 10{sup 12} ppp. A multitude of intensity related effects must be overcome in order to meet this goal including suppression of coherent dipole instabilities of transverse oscillations which manifest themselves as a sudden drop in the beam current. In this report we present the results of observation of these instabilities at different tune, coupling and chromaticity settings and discuss possible cures.
Date: May 1, 2012
Creator: Alexahin, Y.; Eddy, N.; Gianfelice-Wendt, E.; Lebedev, V.; Marsh, W.; Pellico, W. et al.
Partner: UNT Libraries Government Documents Department

The machine protection system for the R&D energy recovery LINAC

Description: The Machine Protection System (MPS) is a device-safety system that is designed to prevent damage to hardware by generating interlocks, based upon the state of input signals generated by selected sub-systems. It protects all the key machinery in the R&D Project called the Energy Recovery LINAC (ERL) against the high beam current. The MPS is capable of responding to a fault with an interlock signal within several microseconds. The ERL MPS is based on a National Instruments CompactRIO platform, and is programmed by utilizing National Instruments' development environment for a visual programming language. The system also transfers data (interlock status, time of fault, etc.) to the main server. Transferred data is integrated into the pre-existing software architecture which is accessible by the operators. This paper will provide an overview of the hardware used, its configuration and operation, as well as the software written both on the device and the server side.
Date: March 28, 2011
Creator: Altinbas, Z.; Kayran, D.; Jamilkowski, J.; Lee, R.C. & Oerter, B.
Partner: UNT Libraries Government Documents Department

PXIE: Project X Injector Experiment

Description: A multi-MW proton facility, Project X, has been proposed and is currently under development at Fermilab. We are planning a program of research and development aimed at integrated systems testing of critical components comprising the front end of the Project X. This program is being undertaken as a key component of the larger Project X R&D program. The successful completion of this program will validate the concept for the Project X front end, thereby minimizing a primary technical risk element within Project X. Integrated systems testing, known as the Project X Injector Experiment (PXIE), will be accomplished with a new test facility under construction at Fermilab and will be completed over the period FY12-16. PXIE will include an H{sup -} ion source, a CW 2.1-MeV RFQ and two superconductive RF (SRF) cryomodules providing up to 25 MeV energy gain at an average beam current of 1 mA (upgradable to 2 mA). Successful systems testing will also demonstrate the viability of novel front end technologies that are expected find applications beyond Project X.
Date: May 1, 2012
Creator: Ostroumov, P.N.; /Argonne; Holmes, S.D.; Kephart, R.D.; Kerby, J.S.; Lebedev, V.A. et al.
Partner: UNT Libraries Government Documents Department

Side extraction duoPIGatron-type ion source.

Description: We have designed and constructed a compact duoPIGatron-type ion source, for possible use in ion implanters, in such the ion can be extracted from side aperture in contrast to conventional duoPIGatron sources with axial ion extraction. The size of the side extraction aperture is 1x40 mm. The ion source was developed to study physical and technological aspects relevant to an industrial ion source. The side extraction duoPIGatron has stable arc, uniformly bright illumination, and dense plasma. The present work describes some of preliminary operating parameters of the ion source using Argon, BF3. The total unanalyzed beam currents are 23 mA using Ar at an arc current 5 A and 13 mA using BF3 gas at an arc current 6 A.
Date: August 26, 2007
Partner: UNT Libraries Government Documents Department


Description: The ERL Prototype project is currently under development at the Brookhaven National Laboratory. The ERL is expected to demonstrate energy recovery of high-intensity beams with a current of up to a few hundred milliamps, while preserving the emittance of bunches with a charge of a few nanocoulombs produced by a high-current SRF gun. To successfully accomplish this task the machine will include beam diagnostics that will be used for accurate characterization of the three dimensional beam phase space at the injection and recirculation energies, transverse and longitudinal beam matching, orbit alignment, beam current measurement, and machine protection. This paper outlines requirements on the ERL diagnostics and describes its setup and modes of operation.
Date: June 25, 2007
Partner: UNT Libraries Government Documents Department

Luminosity Lifetime

Description: In a symmetric or 'energy transparent' relativistic collider, the luminosity is given by L = N{sup 2}f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y} where N is the number of electrons or positrons per bunch, {sigma}*{sub x} ({sigma}*{sub y}) is the horizontal (vertical) rms beam size at the interaction point (IP), and f{sub c} is the collision frequency. If the beam sizes remain constant as the luminosity decreases, then the time dependence of luminosity is contained entirely in the time dependence of the beam currents, i.e., N O N(t), and we can rewrite the equation as L(t) = N{sup 2}(t)f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y}. There are two distinct categories for luminosity loss. In the first category are loss processes due to collisions between the two beams, that is, processes associated directly with the luminosity. In the second category (see below) are single-beam loss processes. The processes in the first category relevant to a high-energy collider are Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}) and 'radiative' Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}{gamma}). In the first process, a beam particle is lost if its angular deflection is beyond the ring's transverse acceptance; in the second process, loss occurs if the beam particle's momentum change is outside the longitudinal acceptance of the ring (typically determined by the RF bucket height).
Date: April 1, 1997
Creator: Zisman, M.S.
Partner: UNT Libraries Government Documents Department

Electrons in a positive-ion beam with solenoid or quadrupole magnetic transport

Description: The High Current Experiment (HCX) is used to study beam transport and accumulation of electrons in quadrupole magnets and the Neutralized Drift-Compression Experiment (NDCX) to study beam transport through and accumulation of electrons in magnetic solenoids. We find that both clearing and suppressor electrodes perform as intended, enabling electron cloud densities to be minimized. Then, the measured beam envelopes in both quadrupoles and solenoids agree with simulations, indicating that theoretical beam current transport limits are reliable, in the absence of electrons. At the other extreme, reversing electrode biases with the solenoid transport effectively traps electrons; or, in quadrupole magnets, grounding the suppressor electrode allows electron emission from the end wall to flood the beam, in both cases producing significant degradation in the beam.
Date: June 4, 2007
Creator: Molvik, A.W.; Kireeff Covo, M.; Cohen, R.; Coleman, J.; Sharp, W.; Bieniosek, F. et al.
Partner: UNT Libraries Government Documents Department

Simulation of a Standing-Wave Free-Electron Laser

Description: The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator (TBA) because microwave power can be extracted more effectively than from a traveling-wave FEL. The standing-wave FEL is modeled in the continuum limit by a set of equations describing the coupling of a one-dimensional beam to a TE{sub 01} rectangular-waveguide mode. Analytic calculations and numerical simulations are used to determine the time variation of the reacceleration field and the prebunching required so that the final microwave energy is the same in all cavities. The microwave energy and phase are found to be insensitive to modest spreads in the beam energy and phase and to errors in the reacceleration field and the beam current, but the output phase appears sensitive to beam-energy errors and to timing jitter.
Date: September 1, 1990
Creator: Sharp, W.M.; Sessler, A.M.; Whittum, D.H. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Beam Comissioning of the PEP-II High Energy Ring

Description: The PEP-II High Energy Ring (HER), a 9 GeV electron storage ring, has been in commissioning since spring 1997. Initial beam commissioning activities focused on systems checkout and commissioning and on determining the behavior of the machine systems at high beam currents. This phase culminated with the accumulation of 0.75 A of stored beam-sufficient to achieve design luminosity--in January 1998 after 3.5 months of beam time. Collisions with the 3 GeV positron beam of the Low Energy Ring (LER) were achieved in Summer of 1998. At high beam currents, collective instabilities have been seen. Since then, commissioning activities for the HER have shifted in focus towards characterization of the machine and a rigorous program to understand the machine and the beam dynamics is presently underway.
Date: November 12, 1998
Creator: Wienands, U.; Anderson, S.; Assmann, R.; Bharadwaj, V.; Cai, Y.; Clendenin, J. et al.
Partner: UNT Libraries Government Documents Department

Low Impedance Bellows for High-current Beam Operations

Description: In particle accelerators, bellows are commonly used to connect beamline components. Such bellows are traditionally shielded to lower the beam impedance. Excessive beam impedance can cause overheating in the bellows, especially in high beam current operation. For an SRF-based accelerator, the bellows must also be particulate free. Many designs of shielded bellows incorporate rf slides or fingers that prevent convolutions from being exposed to wakefields. Unfortunately these mechanical structures tend to generate particulates that, if left in the SRF accelerator, can migrate into superconducting cavities, the accelerator's critical components. In this paper, we describe a prototype unshielded bellows that has low beam impedance and no risk of particulate generation.
Date: July 1, 2012
Creator: Wu, G.; Nassiri, A.; Waldschmidt, G. J.; Yang, Y.; Feingold, J. J.; Mammosser, J. D. et al.
Partner: UNT Libraries Government Documents Department

Toward more precise beam position measurements

Description: For the past year or so we have been examining the properties and limitations of the beam bugs in use in the ETA program at LLNL with a view toward improving the accuracy of beam position and current measurements. When considering measurements of beam position, it is very important to distinguish between relative and absolute position measurements. A relative position measurement determines only the amplitude and direction of the motion of the beam within the transport tube. If one knew where the beam was, one could determine its new position. A relative measurement is essentially independent of errors in mechanical fabrication or electrical components. The minimum measurable displacement is only limited by the strength of the electrical signals or the signal to noise ratio of the position signal. An absolute position measurement is much more challenging. All inaccuracies in mechanical components and fabrication, electrical components, installation and assembly errors must be considered and controlled along with the issues common to relative position measurements. However, if the object is to strike a small specific point on a target or pass the beam through a small hole, absolute beam position measurements are required. The following is a summary of our progress including conclusions and recommendations for developments and improvements. This is, of course, only a step in beam bug development and there is plenty of room for others to contribute.
Date: May 12, 1999
Creator: Clark, J C; Fessenden, T J & Holmes, C
Partner: UNT Libraries Government Documents Department

Polarization in SuperB

Description: SuperB, the 2nd-generation B-Factory with a luminosity of 10{sup 36}/cm{sup 2}/s proposed for LNF, is being designed from the start to be capable of providing a spin-polarized electron beam in the low-energy ring (LER) with longitudinal polarization at the interaction point. Due to the high luminosity at moderate beam current the beam lifetime is short (a few minutes), and a polarized injector will be used. Spin rotators have been designed and the equilibrium polarization evaluated. It will be shown that an average polarization of about 70% can be expected.
Date: June 21, 2012
Creator: Wienands, Ulrich; /SLAC; Nosochkov, Yuri; /SLAC; Sullivan, Michael; /SLAC et al.
Partner: UNT Libraries Government Documents Department