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Spherical Aberration Corrections for the Electrostatic Gridded Lens

Description: Two methods of spherical aberration corrections of an electrostatic gridded lens have been studied with ray tracing simulations. Both methods are based on modifying electrostatic field on the periphery of the lens. In a simplest case such modification is done by extending the part of the grid support on its radial periphery in axial direction. In alternative method the electric field on the radial periphery of the lens is modified by applying an optimum voltage on an electrically isolated correcting electrode. It was demonstrated, that for a given focal length the voltage on this lens can be optimized for minimum aberration The performance of lenses is presented as a lens contribution to the beam RMS normalized emittance.
Date: May 1, 2008
Creator: Pikin,A.
Partner: UNT Libraries Government Documents Department

UCLA/FNPL Underdense Plasma Lens Experiment: Results and Analysis

Description: Focusing of a 15 MeV, 16 nC electron bunch by a gaussian underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated. The strong 1.9 cm focal length plasma lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Time resolved measurements of the focused electron bunch are also reported and compared to simulations.
Date: August 4, 2006
Creator: Thompson, M C; Badakov, H; Rosenzweig, J B; Travish, G; Fliller, R; Kazakevich, G M et al.
Partner: UNT Libraries Government Documents Department

Observations of underdense plasma lens focusing of relativistic electron beams

Description: Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion.
Date: June 1, 2007
Creator: Thompson, M. C.; Badakov, H.; Rosenzweig, J. B.; Travish, G.; Fliller, R.; Kazakevich, G. M. et al.
Partner: UNT Libraries Government Documents Department

Magnetic optics for proton radiography

Description: High energy protons of 10 to 50 GeV can be used to radiograph dense objects. Because the transmitted beam particles undergo multiple coulomb scattering (MCS) in the object, a magnetic lens system is used to focus the particles exiting each point of the object onto a distant image plane. Without the lens, the MCS would seriously blur the radiographic image. Correlations can be introduced in the illuminating beam to cancel a major part of the chromatic and geometric aberrations in the lens, while providing locations inside the lens where the rays are sorted by MCS angle. This allows the introduction of angle cut apertures to aid material identification. The requirement for a matched multistage lens system with successively smaller angle-cut apertures leads to the use of minus-identity ({minus}I) lenses, in which the angle sorting is in the longitudinal mid plane of the lens, and the exit beam correlations are the same as the input correlations. A single stage {minus}I lens has been successfully tested at Brookhaven with 10-GeV protons and another is being used in dynamic experiments with 0.8-GeV protons at Los Alamos. The resolution achievable at higher energies is briefly surveyed.
Date: October 1, 1997
Creator: Mottershead, C.T. & Zumbro, J.D.
Partner: UNT Libraries Government Documents Department

Hexagonal close-packed arrays of optical fibers for partitioning a laser beam into individual beamlets: Analysis and prototype fabrication

Description: Hexagonally close-packed arrays of optical fibers were investigated for partitioning a laser beam into individual beamlets for distribution to remote and variously located regions for experimental purposes. Equations were derived giving the efficiency of coupling the laser beam into the fibers as a function of the fiber cross section geometry and the number of fibers in a given hexagonal array, assuming that the laser beam just filled the outermost fibers in the array. The analysis was done also for the case in which a small lens was used in conjunction with each fiber in the array. For the lens fiber combination, the effect of spherical aberration was calculated and equations were derived giving the location and radius of the so-called circle of least confusion as a function of the lens geometry. The effects of aberration were also compared with the calculated diffraction limited focal spot size for a lens in the array. The effect of misalignment of a lens relative to the laser beam was analyzed with regard to the efficiency of energy coupled into the mating fiber. A prototype array was fabricated utilizing a hexagonal array of 61 fibers.
Date: July 1, 1997
Creator: Klingsporn, P.E.
Partner: UNT Libraries Government Documents Department

PLASMA LENS FOR US BASED SUPER NEUTRINO BEAM AT EITHER FNAL OR BNL.

Description: The plasma lens concept is examined as an alternative to focusing horns and solenoids for a neutrino beam facility. The concept is based on a combined high-current lens/target configuration. Current is fed at an electrode located downstream from the beginning of the target where pion capturing is needed. The current is carried by plasma outside the target. A second plasma lens section, with an additional current feed, follows the target. The plasma is immersed in a relatively small solenoidal magnetic field to facilitate its current profile shaping to optimize pion capture. Simulations of the not yet fully optimized configuration yielded a 25% higher neutrino flux at a detector situated at 3 km from the target than the horn system for the entire energy spectrum and a factor of 2.47 higher flux for neutrinos with energy larger than 3 GeV. A major advantage of plasma lenses is in background reduction. In anti-neutrino operation, neutrino background is reduced by a factor of close to 3 for the whole spectrum, and for and for energy larger than 3 GeV, neutrino background is reduced by a factor of 3.6. Plasma lenses have additional advantages: larger axial currents, high signal purity: minimal neutrino background in anti-neutrino runs. The lens medium consists of plasma, consequently, particle absorption and scattering is negligible. Withstanding high mechanical and thermal stresses in a plasma is not an issue.
Date: June 25, 2007
Creator: HERSHCOVITCH,A.; WENG, W.; DIWAN, M.; GALLARDO, J.; KIRK, H.; JOHNSON, B. et al.
Partner: UNT Libraries Government Documents Department

Plasma Lens for Muon and Neutrino Beams

Description: The plasma lens is examined as an alternate to focusing horns and solenoids for use in a neutrino or muon beam facility. The plasma lens concept is based on a combined high-energy lens/target configuration. The current is fed at electrodes located upstream and downstream from the target where pion capturing is needed. The current flows primarily in the plasma, which has a lower resistivity than the target. A second plasma lens section, with an additional current feed, follows the target to provide shaping of the plasma for optimum focusing. The plasma lens is immersed in an additional solenoid magnetic field to facilitate the plasma stability. The geometry of the plasma is shaped to provide optimal pion capture. Simulations of this plasma lens system have shown a 25% higher neutrino production than the horn system. Plasma lenses have the additional advantage of negligible pion absorption and scattering by the lens material and reduced neutrino contamination during anti-neutrino running. Results of particle simulations using plasma lens will be presented.
Date: June 23, 2008
Creator: Kahn,S.A.; Korenev, S.; Bishai, M.; Diwan, M.; Gallardo, J.C.; Hershcovitch, A. et al.
Partner: UNT Libraries Government Documents Department

Results from the UCLA/FNPL underdense plasma lens experiment

Description: A gaussian underdense plasma lens with peak density 5 x 10{sup 12} cm{sup -3} and a full width half maximum (FWHM) length of 2.2 cm has been used to focus a relativistic electron beam. This plasma lens is equivalent in strength to a quadrupole magnet with a 150 T/m field gradient. The lens focused a 15 MeV, 16 nC electron beam with initial dimensions {sigma}{sub x,y} {approx} 650 {micro}m and {sigma}{sub z} {approx} 6.5 mm onto an optical transition radiation (OTR) screen {approx}2 cm downstream of the lens. The average transverse area of the plasma focused electron beam was typically demagnified by a factor of 23. The evolution of the beam envelope in the area near the beam waist was measured for both round beams and asymmetric beams with x:y aspect ratios as large as 1:5. The light from the OTR screen in the round beam case was also imaged into a streak camera in order to directly measure the correlation between z and {sigma}{sub r} within the beam.
Date: January 1, 2007
Creator: Thompson, M.C.; Badakov, H.; Rosenzweig, J.B.; Travish, G.; /UCLA; Edwards, H. et al.
Partner: UNT Libraries Government Documents Department

RESULTS FROM THE UCLA/FNPL UNDERDENSE PLASMA LENS EXPERIMENT

Description: A gaussian underdense plasma lens with peak density 5 x 10{sup 12} cm{sup -3} and a full width half maximum (FWHM) length of 2.2 cm has been used to focus a relativistic electron beam. This plasma lens is equivalent in strength to a quadrupole magnet with a 150 T/m field gradient. The lens focused a 15 MeV, 16 nC electron beam with initial dimensions {sigma}{sub x,y} {approx} 650 {micro}m and {sigma}{sub z} {approx} 6.5 mm onto an optical transition radiation (OTR) screen {approx}2 cm downstream of the lens. The average transverse area of the plasma focused electron beam was typically demagnified by a factor of 23. The evolution of the beam envelope in the area near the beam waist was measured for both round beams and asymmetric beams with x:y aspect ratios as large as 1:5. The light from the OTR screen in the round beam case was also imaged into a streak camera in order to directly measure the correlation between z and {sigma}{sub r} within the beam.
Date: April 18, 2006
Creator: Thompson, M C; Badakov, H; Rosenzweig, J B; Travish, G; Edwards, H; Fliller, R et al.
Partner: UNT Libraries Government Documents Department

Trip Report-Visit to CERN July 5 to August 5, 1985

Description: The present visit to CERN was as a result of an invitation from Dr. Colin Johnson of the Antiproton Accumulator (AA) group. Two activities were planned for this visit. First, the second beam test of one of the original Fermilab lithium lenses (serial No.2). Second, the installation and beam tests for a new Fermilab lens of improved design (serial No.5). It should be mentioned here that CERN, after realizing the possible gains to be obtained, has started a considerable development effort in short focal length lenses. Presently they have 3 operational lithium lenses, transformers and power supplies for tests. They are in the process of constructing 3 other transformers and designing lenses of 4 cm diameter (twice the present Fermilab lenses). Fermilab should devote some added effort in the field to maintain the initiative. The first beam test of lens No.2 was performed during the summer of 1983, when the lens was used as an antiproton collecting lens. For this test the original lens was used as a strong focusing element in the 26 GeV proton beam in conjunction with a current carrying target Preliminary tests for this geometry were conducted during 1984, when the lens was exposed to over 2*E6 pulses at 320kAmps and 1.3*E13 protons per pulse. Lens No.5 was installed as an antiproton collecting lens, immediately following the AA production target, in a geometry similar to the one designed for the Tevatron 1 project at Fermilab. Targets of a different design than the one use normally at CERN were also required. After completion of the antiproton yield measurements and optimization the lens was left in the beam during regular operation for antiproton accumulation. During antiproton accumulation for the Lear accelerator new records were achieved on the accumulation yield and accumulation rate of antiprotons for the AA machine. ...
Date: September 13, 1985
Creator: Hogvat, C.
Partner: UNT Libraries Government Documents Department

GROUNDING OF BETA SOURCES BY AN AUXILIARY ALPHA SOURCE

Description: A Po/sup 210/ source was used to furnish a reliab1e ground for both electron and positron sources. This was done to prevent the electron and positron sources from charging during BETA spectral studies in magnetic lens spectrometers. An approximately 20- mu c Po/sup 210/ source was placed 1.2 in. behind a 4- mu c Na/sup 2 / 2>s positron emitter backed by 20- mu g/cm/sup 2/ Formvar in the spectrometer; this arrangement resulted in a charging rate decrease of approximately 80%. When the source was placed 0.5 in. away, no charging was detectable over a period of more than one week. The discharge is attributed mainly to the loss of electrons from the source and backing caused by ionization of alpha particles since few alpha particles are stopped near the source. (B.O.G.)
Date: December 1, 1960
Creator: Nichols, R.T. & Jensen, E.N.
Partner: UNT Libraries Government Documents Department

UV laser ionization and electron beam diagnostics for plasma lenses

Description: A comprehensive study of focusing of relativistic electron beams with overdense and underdense plasma lenses requires careful control of plasma density and scale lengths. Plasma lens experiments are planned at the Beam Test Facility of the LBL Center for Beam Physics, using the 50 MeV electron beam delivered by the linac injector from the Advanced Light Source. Here we present results from an interferometric study of plasmas produced in tri-propylamine vapor with a frequency quadrupled Nd:YAG laser at 266 nm. To study temporal dynamics of plasma lenses we have developed an electron beam diagnostic using optical transition radiation to time resolve beam size and divergence. Electron beam ionization of the plasma has also been investigated.
Date: April 1, 1995
Creator: Govil, R.; Volfbeyn, P. & Leemans, W.
Partner: UNT Libraries Government Documents Department

The focusing properties of the positron-capture solenoidal lens

Description: This note concerns the focusing properties of the positron-capture solenoid. Such a solenoid will be placed before the entrance of the 450 MeV positron linear-accelerator injector in the APS. The 1.25 A, 40 ns electron beam is accelerated in the 200 MeV electron linac. This beam is then focused onto a 3 mm diameter spot at the 7 mm thick tungsten target. By the process of multiple nuclear-scattering the target generates the positron particles. These positrons, in general, can have a large diverging angle. In order to capture these rapidly diverging positrons, a relatively strong focusing lens is placed close to the converter. In this case a magnetic solenoidal lens has an advantage over the usual quadrupole lens because of its larger phase-space acceptance. In particular, the solenoidal lens is noted for its capability of controlling the spin direction of polarized ions. The authors first wrote down the expression for the magnetic field distribution on the axis for the solenoidal lens. From this expression they derive the expressions for the first- and second-order field distributions at any point in the region. They then calculate and compare the focal powers at various distances off the axis. Further, they calculate and include the third- and fourth-order components of the fields and compare them with the previous results. Finally, they briefly consider the particle trajectories through these fields and present the result in terms of the particle motion in phase space.
Date: June 1, 1988
Creator: Yoon, M. & Mavrogenes, G.
Partner: UNT Libraries Government Documents Department

Neutrino beams using the main injector

Description: TM-1946 summarizes the status of the NuMI project. This note presents more details on the technical design of the various NUMI beams. Several beam]Line options are investigated for producing neutrinos--(l) a wide-band beam(WBB) using horns, (2) a beam using a single lithium Lens, and (3) a two stage narrow-band beam(NBB) using a Lithium Lens, quadrupoles and dipoles. The first two are designed to maximize the muon neutrino event rate; the third is designed to have a tunable range of parent momenta from 5-60 GeV/c. In the context of NuMI, the Double Horns-and its target were concepts first described in 1991. The lithium Lens has been used at Fermilab for pbar production for several years. With recent upgrades, it forms the basis of what will be used by NuMI. Narrow band beams using conventional dipoles and quadrupoles have been studied, but have less acceptance than one using a lithium lens. The following practical limits are imposed on each of the systems: (1) Horns: The necks will not have a smaller radius than 1 cm; the maximum current will not exceed 170 kAmp. Keeping the inside diameter large allows the primary proton beam to vary in position, yet not strike the fragile neck. In addition, there is a trade-off between decreasing the radius and increasing the wall thickness to maintain the required strength in the conductor material. (2) Magnets: Reasonable conventional designs are used. The maximum gradient for quadrupoles is 12 kG/half-aperture; the maximum field for dipoles is about 16 kG; larger apertures scale the gradients and fields downward. Although not a primary consideration, optically it is desirable for the magnification in each plane to be comparable (within a factor of 2 or 3 is OK). (3) Lithium Lens: The maximum radius is 1.0 cm with a maximum gradient of 100 kG/cm. ...
Date: November 1, 1995
Creator: Malensek, A.J.
Partner: UNT Libraries Government Documents Department