66 Matching Results

Search Results

Advanced search parameters have been applied.

Modified betatron for ion beam fusion

Description: An intense neutralized ion beam can be injected and trapped in magnetic mirror or tokamak geometry. The details of the process involve beam polarization so that the beam crosses the fringing fields without deflection and draining the polarization when the beam reaches the plasma. Equilibrium requires that a large betatron field be added in tokamak geometry. In mirror geometry a toroidal field must be added by means of a current along the mirror axis. In either case, the geometry becomes that of the modified betatron which has been studied experimentally and theoretically in recent years. We consider beams of d and t ions with a mean energy of 500 kev and a temperature of about 50 kev. The plasma may be a proton plasma with cold ions. It is only necessary for beam trapping or to carry currents. The ion energy for slowing down is initially 500 kev and thermonuclear reactions depend only on the beam temperature of 50 kev which changes very slowly. This new configuration for magnetic confinement fusion leads to an energy gain of 10--20 for d-t reactions whereas previous studies of beam target interaction predicted a maximum energy gain of 3--4. The high beam energy available with pulsed ion diode technology is also essential for advanced fuels. 16 refs., 3 figs.
Date: January 1, 1986
Creator: Rostoker, N. & Fisher, A.
Partner: UNT Libraries Government Documents Department

Localized ion milling of metallic and ceramic TEM specimens

Description: The utility of localized ion milling in the preparation of metallic and ceramic specimens for TEM and AEM is being evaluated from the standpoint of optimizing procedures and identifying limitations and milling characteristics. The equipment used was a Gatan model 645 precision ion milling system (PIMS). This device is a scanning ion beam instrument with which selected areas of a sample can be imaged by either secondary electron or secondary ion signals and selectively ion milled in a small region within the imaged area. The 1 to 10 keV ion beam can be focussed to a 2 ..mu..m spot. Specimens are thinned without removing them from the electron microscope specimen holder.
Date: January 1, 1986
Creator: Fisher, A.T. & Bentley, J.
Partner: UNT Libraries Government Documents Department

Subsidizing solar energy: the role of tax credits, loans, and warranties

Description: It is generally agreed that solar energy is an appropriate technology. It is further agreed that its use ought to be subsidized by appropriate governmental action. There is not, however, a consensus as to just why solar energy is desirable, or what constitutes appropriate action. In this paper some arguments are considered for a subsidy and are related to a specific proposal. First, some of the arguments that have been advanced in favor of subsidizing solar energy are reviewed. Next, an additional argument, which seems to offer a strong rationale for a subsidy of a somewhat unconventional sort--a government-backed service warranty--is proposed. Then the argument for the warranty is presented, along with an argument for a subsidy to overcome high front-end costs. Finally, some estimates of the budget costs of a warranty program are presented.
Date: March 1, 1978
Creator: Berman, S.M. & Fisher, A.C.
Partner: UNT Libraries Government Documents Department

Scaling of gain with energy spread and energy in the PEP FEL

Description: The Sag Harbor paper on the PEP FEL discusses the scaling of various FEL parameters with energy spread {sigma}{sub {var epsilon}}. I will repeat some of this material here and then examine the benefit of increasing the energy spread. How much energy spread can be achieved with damping wigglers is the next topic. Finally, I consider the dependence of gain and saturation length on beam energy and undulator field.
Date: July 13, 1992
Creator: Fisher, A.S.
Partner: UNT Libraries Government Documents Department

Injection Related Background due to the Transverse Feedback

Description: The background in the BaBar detector is especially high during injection, when most components are actually having reduced voltages. The situation is worse for the beam in High Energy Ring (HER) when the LER beam is present. It was found that the transverse feedback system plays an important role when stacking more charge on top of existing bunches. Lowering the feedback gain helped and it was realized later that the best scenario would be to gate off the feedback for only the one bunch, which got additional charge injected into it. The explanation is that the blown-up, but centered, original HER bunch plus the small injected off-axis bunch (each with half the charge) would stay in the ring if not touched, but the feedback system sees half the offset and wants to correct it, therefore disturbing and scraping the blown-up part.
Date: March 18, 2008
Creator: Decker, F.J.; Akre, R.; Fisher, A.; Iverson, R.; Weaver, M. & /SLAC
Partner: UNT Libraries Government Documents Department

Bunch Length and Impedance Measurements at SPEAR3

Description: Streak camera measurements were made at SPEAR3 to characterize longitudinal coupling impedance. For the nominal optics, data was taken at three rf voltages and a single-bunch current range of 0-20mA. Both bunchcentroid phase shift and bunch lengthening were recorded to extract values for resistive and reactive impedance. An (R+L) and a Q=1 model were then back-substituted into the Haissinski equation and compared with raw profile data. In the short bunch (low-{alpha}) mode, distribution 'bursting' was observed.
Date: November 2, 2011
Creator: Corbett, W.J.; Cheng, W.X.; Fisher, A.S.; Huang, X. & /SLAC
Partner: UNT Libraries Government Documents Department

An Efficient Vector Finite Element Method for Nonlinear Electromagnetic Modeling

Description: We have developed a mixed Vector Finite Element Method (VFEM) for Maxwell's equations with a nonlinear polarization term. The method allows for discretization of complicated geometries with arbitrary order representations of the B and E fields. In this paper we will describe the method and a series of optimizations that significantly reduce the computational cost. Additionally, a series of test simulations will be presented to validate the method. Finally, a nonlinear waveguide mode mixing example is presented and discussed.
Date: June 27, 2006
Creator: Fisher, A C; White, D A & Rodrigue, G H
Partner: UNT Libraries Government Documents Department

Detection of Instrumental Drifts in the PEP II LER BPM System

Description: During the last PEP-II run a major goal was to bring the Low-Energy Ring optics as close as possible to the design. A large number of BPMs exhibited sudden artificial jumps that interfered with this effort. The source of the majority of these jumps had been traced to the filter-isolator boxes (FIBs) near the BPM buttons. A systematic approach to find and repair the failing units had been developed and implemented. Despite this effort, the instrumental orbit jumps never completely disappeared. To trace the source of this behavior a test setup, using a spare Bergoz MX-BPM processor (kindly provided by SPEAR III at SSRL), was connected in parallel to various PEP-II BPM processors. In the course of these measurements a slow instrumental orbit drift was found which was clearly not induced by a moving positron beam. Based on the size of the system and the limited time before PEP-II closes in Oct.2008, an accelerator improvement project was initiated to install BERGOZ BPM-MX processors close to all sextupoles.
Date: November 7, 2007
Creator: Wittmer, W.; Fisher, A.S.; Martin, D.J.; Sebek, J.J. & /SLAC
Partner: UNT Libraries Government Documents Department

Turn-by-Turn and Bunch-by-Bunch Transverse Profiles of a Single Bunch in a Full Ring

Description: The apparatus described in this paper can image the evolution of the transverse profile of a single bunch, isolated from a full PEP-II ring of 1500 bunches. Using this apparatus there are two methods of single bunch imaging; bunch-by-bunch beam profiling can image every bunch in the ring a single bunch at a time with the images of sequential bunches being in order, allowing one to see variations in beam size along a train. Turn-by-turn beam profiling images a single bunch on each successive turn it makes around the ring. This method will be useful in determining the effect that an injected bunch has on a stable bunch as the oscillations of the injected bunch damp out. Turn-by-turn imaging of the synchrotron light uses a system of lenses and mirrors to image many turns of both the major and minor axis of a single bunch across the photocathode of a gateable camera. The bunch-by-bunch method is simpler: because of a focusing mirror used in porting the light from the ring, the synchrotron light from the orbiting electrons becomes an image at a certain distance from the mirror; and since the camera does not use a lens, the photocathode is set exactly at this image distance. Bunch-by-bunch profiling has shown that in the Low Energy Ring (LER) horizontal bunch size decreases along a train. Turn-by-turn profiling has been able to image 100 turns of a single bunch on one exposure of the camera. The turn-by-turn setup has also been able to image 50 turns of the minor axis showing part of the damping process of an oscillating injected charge during a LER fill. The goal is to image the damping of oscillations of injected charge for 100 turns of both the major and minor axis throughout the damping process during trickle ...
Date: December 15, 2005
Creator: Kraus, R.; /Nevada U., Reno; Fisher, A.S. & /SLAC
Partner: UNT Libraries Government Documents Department

A high stability Nd:YAG photocathode drive laser

Description: A versatile, highly stable, reliable Nd:YAG laser is in operation at Brookhaven Accelerator Test Facility (ATF) for illuminating a metal photocathode RF electron gun. This system addresses stringent requirements on pulse duration, pulse timing jitter, pulse energy, spatial profile, and pointing imposed by electron accelerator experiments. This paper describes the oscillator operation, (which also includes control of a semicconductor switch for ATF`s high power CO{sub 2} laser), beam transport to the cathode, etc.
Date: December 31, 1995
Creator: Babzien, M.; Pogorelsky, I.; Srinivasan-Rao, T. & Fisher, A.
Partner: UNT Libraries Government Documents Department

Materials science applications of a 120 kV FEG TEM/STEM: Triskaidekaphilia

Description: The introduction by several manufacturers of 200kV transmission electron microscopes (TEM) equipped with field emission guns affords the opportunity to assess their potential impact on materials science by examining applications of similar 100-120kV instruments that have been in use for more than a decade. This summary is based on results from a Philips EM400T/FEG configured as an analytical electron microscope (AEM) with a 6,585 scanning transmission (STEM) unit, EDAX 9100/70 or 9900 energy dispersive X-ray spectroscopy (EDS) systems, and Gatan 607 serial- or 666 parallel-detection electron energy-loss spectrometers (EELS). Examples in four areas that illustrate applications that are impossible or so difficult as to be impracticable with conventional thermionic electron guns are described.
Date: January 1, 1991
Creator: Bentley, J.; Fisher, A.T.; Kenik, E.A. & Wang, Z.L.
Partner: UNT Libraries Government Documents Department

Terahertz Light Source and User Area at FACET

Description: FACET at SLAC provides high charge, high peak current, low emittance electron beam that is bunched at THz wavelength scale during its normal operation. A THz light source based coherent transition radiation (CTR) from this beam would potentially be the brightest short-pulse THz source ever constructed. Efforts have been put into building this photon source together with a user area, to provide a platform to utilize this unique THz radiation for novel nonlinear and ultrafast phenomena researches and experiments. Being a long-time underutilized portion of the electromagnetic spectrum, terahertz (100 GHz {approx} 10 THz) spectral range is experiencing a renaissance in recent years, with broad interests from chemical and biological imaging, material science, telecommunication, semiconductor and superconductor research, etc. Nevertheless, the paucity of THz sources especially strong THz radiation hinders both its commercial applications and nonlinear processes research. FACET - Facilities for Accelerator science and Experimental Test beams at SLAC - provides 23 GeV electron beam with peak currents of {approx} 20 kA that can be focused down to 100 {mu}m{sup 2} transversely. Such an intense electron beam, when compressed to sub-picosecond longitudinal bunch length, coherently radiates high intensity EM fields well within THz frequency range that are orders of magnitude stronger than those available from laboratory tabletop THz sources, which will enable a wide variety of THz related research opportunities. Together with a description of the FACET beamline and electron beam parameters, this paper will report FACET THz radiation generation via coherent transition radiation and calculated photon yield and power spectrum. A user table is being set up along the THz radiation extraction sites, and equipped with various signal diagnostics including THz power detector, Michelson interferometer, sample stages, and sets of motorized optical components. This setup will also be presented. Potential THz research areas including studies of magnetism, ferroelectric ...
Date: November 8, 2011
Creator: Wu, Z.; Li, S.Z.; Litos, M.; Fisher, A.D.; Hogan, M.J. & /SLAC
Partner: UNT Libraries Government Documents Department

Interface Reconstruction in Two-and Three-Dimensional Arbitrary Lagrangian-Euderian Adaptive Mesh Refinement Simulations

Description: Modeling of high power laser and ignition facilities requires new techniques because of the higher energies and higher operational costs. We report on the development and application of a new interface reconstruction algorithm for chamber modeling code that combines ALE (Arbitrary Lagrangian Eulerian) techniques with AMR (Adaptive Mesh Refinement). The code is used for the simulation of complex target elements in the National Ignition Facility (NIF) and other similar facilities. The interface reconstruction scheme is required to adequately describe the debris/shrapnel (including fragments or droplets) resulting from energized materials that could affect optics or diagnostic sensors. Traditional ICF modeling codes that choose to implement ALE + AMR techniques will also benefit from this new scheme. The ALE formulation requires material interfaces (including those of generated particles or droplets) to be tracked. We present the interface reconstruction scheme developed for NIF's ALE-AMR and discuss how it is affected by adaptive mesh refinement and the ALE mesh. Results of the code are shown for NIF and OMEGA target configurations.
Date: August 28, 2007
Creator: Masters, N D; Anderson, R W; Elliott, N S; Fisher, A C; Gunney, B T & Koniges, A E
Partner: UNT Libraries Government Documents Department

Debris and Shrapnel Mitigation Procedure for NIF Experiments

Description: All experiments at the National Ignition Facility (NIF) will produce debris and shrapnel from vaporized, melted, or fragmented target/diagnostics components. For some experiments mitigation is needed to reduce the impact of debris and shrapnel on optics and diagnostics. The final optics, e.g., wedge focus lens, are protected by two layers of debris shields. There are 192 relatively thin (1-3 mm) disposable debris shields (DDS's) located in front of an equal number of thicker (10 mm) main debris shields (MDS's). The rate of deposition of debris on DDS's affects their replacement rate and hence has an impact on operations. Shrapnel (molten and solid) can have an impact on both types of debris shields. There is a benefit to better understanding these impacts and appropriate mitigation. Our experiments on the Omega laser showed that shrapnel from Ta pinhole foils could be redirected by tilting the foils. Other mitigation steps include changing location or material of the component identified as the shrapnel source. Decisions on the best method to reduce the impact of debris and shrapnel are based on results from a number of advanced simulation codes. These codes are validated by a series of dedicated experiments. One of the 3D codes, NIF's ALE-AMR, is being developed with the primary focus being a predictive capability for debris/shrapnel generation. Target experiments are planned next year on NIF using 96 beams. Evaluations of debris and shrapnel for hohlraum and capsule campaigns are presented.
Date: September 4, 2007
Creator: Eder, D; Koniges, A; Landen, O; Masters, N; Fisher, A; Jones, O et al.
Partner: UNT Libraries Government Documents Department

Report on Modifications to the BX12 and BX13 BC1 Dipoles

Description: Emittance growth seen during the last commissioning run in the bunch compressor optics section, BC1, was blamed on inadequate dipole field quality. The significant linear and nonlinear field non-uniformities generated large horizontal dispersion errors beyond BC1. The linear dispersion after BC1 was corrected using two small 'corrector' quadrupoles placed in BC1 for this purpose, but the remaining nonlinear field caused growth of the normalized horizontal emittance of 40% or more. At best {gamma}{epsilon}{sub x} went from 1.2 {micro}m before BC1 up to 1.7 {micro}m after BC1. The problem was magnified by the larger-than-design energy spread in BC1 due to a long initial bunch length. To improve the field quality we decided to modify the two 'inner dipoles', BX12 and BX13, of the four magnet chicane during the four month down time in the Fall of 2007. Only the two inner dipoles were chosen because of the limited time available and the fact that the beam is particularly sensitive to field quality of the inner dipoles due to its very large transverse size when going through them. The modifications were completed in November and included new poles and a new pinning scheme. The outer dipoles were left unchanged.
Date: November 23, 2010
Creator: Welch, James; DeBarge, S.; Emma, P.; Fisher, A.; Li, N.; Wu, J. et al.
Partner: UNT Libraries Government Documents Department

A high-power picosecond Nd:YAG/CO{sub 2} laser system for electron guns, laser acceleration and FEL

Description: Fourth-harmonic Nd:YAG pulses illuminating a microwave linear accelerator`s photoinjector generates electron bunches in trains for FEL experiments, or in a single pulse for laser acceleration. A multi-gigawatt CO{sub 2} laser switched by the ND:YAG fundamental delivers 50-ps pulses for Inverse Cherenkov, Inverse FEL, or Grating Linac electron acceleration experiments.
Date: December 31, 1994
Creator: Babzien, M.; Ben-Zvi, I.; Fisher, A.S.; Kusche, K.; Pogorelsky, I.V. & Srinivasan-Rao, T.
Partner: UNT Libraries Government Documents Department

Inverse free-electron laser accelerator development

Description: The study of the Inverse Free-Electron Laser, as a potential mode of electron acceleration, has been pursued at Brookhaven National Laboratory for a number of years. More recent studies focused on the development of a low energy (few GeV), high gradient, multistage linear accelerator. The authors are presently designing a short accelerator module which will make use of the 50 MeV linac beam and high power (2 {times} 10{sup 11} W) CO{sub 2} laser beam of the Accelerator Test Facility (ATF) at the Center for Accelerator Physics (CAP), Brookhaven National Laboratory. These elements will be used in conjunction with a fast excitation (300 {mu}sec pulse duration) variable period wiggler, to carry out an accelerator demonstration stage experiment.
Date: June 1, 1994
Creator: Fisher, A.; Gallardo, J.; Steenbergen, A. van; Sandweiss, J. & Fang, J. M.
Partner: UNT Libraries Government Documents Department

40-{angstrom} FEL designs for the PEP storage ring

Description: We explore the use of the 2.2-km PEP storage ring at SLAC to drive a 40-{Angstrom} free-electron laser in the self-amplified spontaneous emission configuration. Various combinations for electron-beam and undulator parameters, as well as special undulator designs, are discussed. Saturation and high peak, in-band, coherent power (460 MW) are possible with a 67-m, hybrid permanent-magnet undulator in a ring bypass. A 100-m, cusp-field undulator can achieve high average, in-band, coherent power (0.25 W) in the main ring. The existing, 25.6-m, Paladin undulator at LLNL, with the addition of optical-klystron dispersive sections, is considered for both peak and average power. 35 refs., 4 figs., 1 tab.
Date: December 31, 1991
Creator: Fisher, A. S.; Gallardo, J. C.; Nuhn, H. D.; Tatchyn, R.; Winick, H. & Pellegrini, C.
Partner: UNT Libraries Government Documents Department

The LCLS Undulator Beam Loss Monitor Readout System

Description: The LCLS Undulator Beam Loss Monitor System is required to detect any loss radiation seen by the FEL undulators. The undulator segments consist of permanent magnets which are very sensitive to radiation damage. The operational goal is to keep demagnetization below 0.01% over the life of the LCLS. The BLM system is designed to help achieve this goal by detecting any loss radiation and indicating a fault condition if the radiation level exceeds a certain threshold. Upon reception of this fault signal, the LCLS Machine Protection System takes appropriate action by either halting or rate limiting the beam. The BLM detector consists of a PMT coupled to a Cherenkov radiator located near the upstream end of each undulator segment. There are 33 BLMs in the system, one per segment. The detectors are read out by a dedicated system that is integrated directly into the LCLS MPS. The BLM readout system provides monitoring of radiation levels, computation of integrated doses, detection of radiation excursions beyond set thresholds, fault reporting and control of BLM system functions. This paper describes the design, construction and operational performance of the BLM readout system.
Date: July 23, 2012
Creator: Dusatko, John; Browne, M.; Fisher, A.S.; Kotturi, D.; Norum, S.; Olsen, J. et al.
Partner: UNT Libraries Government Documents Department

Bunch Length Measurements in SPEAR3

Description: A series of bunch length measurements were made in SPEAR3 for two different machine optics. In the achromatic optics the bunch length increases from the low-current value of 16.6ps rms to about 30ps at 25ma/bunch yielding an inductive impedance of -0.17{Omega}. Reducing the momentum compaction factor by a factor of {approx}60 [1] yields a low-current bunch length of {approx}4ps rms. In this paper we review the experimental setup and results.
Date: November 28, 2007
Creator: Corbett, W.J.; Fisher, A.; Huang, X.; Safranek, J.; Sebek, J.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Modeling Warm Dense Matter Experiments using the 3D ALE-AMR Code and the Move Toward Exascale Computing

Description: The Neutralized Drift Compression Experiment II (NDCX II) is an induction accelerator planned for initial commissioning in 2012. The final design calls for a 3 MeV, Li+ ion beam, delivered in a bunch with characteristic pulse duration of 1 ns, and transverse dimension of order 1 mm. The NDCX II will be used in studies of material in the warm dense matter (WDM) regime, and ion beam/hydrodynamic coupling experiments relevant to heavy ion based inertial fusion energy. We discuss recent efforts to adapt the 3D ALE-AMR code to model WDM experiments on NDCX II. The code, which combines Arbitrary Lagrangian Eulerian (ALE) hydrodynamics with Adaptive Mesh Refinement (AMR), has physics models that include ion deposition, radiation hydrodynamics, thermal diffusion, anisotropic material strength with material time history, and advanced models for fragmentation. Experiments at NDCX-II will explore the process of bubble and droplet formation (two-phase expansion) of superheated metal solids using ion beams. Experiments at higher temperatures will explore equation of state and heavy ion fusion beam-to-target energy coupling efficiency. Ion beams allow precise control of local beam energy deposition providing uniform volumetric heating on a timescale shorter than that of hydrodynamic expansion. The ALE-AMR code does not have any export control restrictions and is currently running at the National Energy Research Scientific Computing Center (NERSC) at LBNL and has been shown to scale well to thousands of CPUs. New surface tension models that are being implemented and applied to WDM experiments. Some of the approaches use a diffuse interface surface tension model that is based on the advective Cahn-Hilliard equations, which allows for droplet breakup in divergent velocity fields without the need for imposed perturbations. Other methods require seeding or other methods for droplet breakup. We also briefly discuss the effects of the move to exascale computing and related computational ...
Date: November 4, 2011
Creator: Koniges, A; Eder, E; Liu, W; Barnard, J; Friedman, A; Logan, G et al.
Partner: UNT Libraries Government Documents Department