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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: April 1, 1995
Creator: Westenskow, G.; Caporaso, G.; Chen, Y.; Houck, T.; Yu, S.; Chattopadhyay, S. et al.
Partner: UNT Libraries Government Documents Department

FIRST EXPERIMENTAL RESULTS FROM DEGAS, THE QUANTUM LIMITED BRIGHTNESS ELECTRON SOURCE

Description: The construction of DEGAS (DEGenerate Advanced Source), a proof of principle for a quantum limited brightness electron source, has been completed at the Lawrence Berkeley National Laboratory. The commissioning and the characterization of this source, designed to generate coherent single electron 'bunches' with brightness approaching the quantum limit at a repetition rate of few MHz, has been started. In this paper the first experimental results are described.
Date: June 23, 2008
Creator: Zolotorev, Max S.; Commins, Eugene D.; Oneill, James; Sannibale, Fernando; Tremsin, Anton & Wan, Weishi
Partner: UNT Libraries Government Documents Department

Beam Dynamics and Instabilities in ELIC Design

Description: In this paper, we report the first study of beam related instabilities in lepton ring of the proposed electron-ion collider beyond the 12 GeV upgrade of CEBAF at Jefferson lab. The design parameters are consistent with PEP-II. Present studies reveal that coupled bunch and two stream instabilities are important issues and we need feedback system. The Medium Energy Electron Ion Collider (MEIC) at Jefferson Lab has been envisioned as future high energy particle accelerator beyond the 12 GeV upgrade of CEBAF. The MEIC will consist of the existing polarized electron source complex with 12 GeV upgrade and a new ion complex with polarized and unpolarized light to medium ions. The conceptual layout is shown in Fig. 1 and the basic parameters in comparison with the similar machines are discussed in Table 1. The maximum permissible collision frequency at 1.5 GHz is dictated by the existing electron machine, allowing the relatively small charge per bunch and large crossing angle resulting in the increased beam stability and high luminosity. In this paper, we present the preliminary study of collective effects for e-ring.
Date: September 1, 2011
Creator: S. Ahmed,B. Yunn,G. Krafft
Partner: UNT Libraries Government Documents Department

First Characterization of a Fully Superconducting RF Photoinjector Cavity

Description: As a first step towards a high brightness, high average current electron source for the BERLinPro ERL a fully superconducting photo-injector was developed by HZB in collaboration with JLab, DESY and the A. Soltan Institute. This cavity-injector ensemble is made up of a 1.6-cell superconducting cavity with a superconducting lead cathode deposited on the half-cell backwall. A superconducting solenoid is used for emittance compensation. This system, including a diagnostics beamline, has been installed in the HoBiCaT facility to serve as a testbed for beam dynamics studies and to test the combination SRF cavity and superconducting solenoid. This paper summarizes the characterization of the cavity in this configuration including Q measurements, dark current tests and field-stability analyses.
Date: September 1, 2011
Creator: Neumann, A; Barday, R; Jankowiak, A; Kamps, T; Knobloch, J; Kugeler, O et al.
Partner: UNT Libraries Government Documents Department

First Demonstration of Electron Beam Generation and Characterization with an All Superconducting Radio-frequency (SRF) Photoinjector

Description: In preparation for a high brightness, high average current electron source for the energy-recovery linac BERLinPro an all superconducting radio-frequency photoinjector is now in operation at Helmholtz-Zentrum Berlin. The aim of this experiment is beam demonstration with a high brightness electron source able to generate sub-ps pulse length electron bunches from a superconducting (SC) cathode film made of Pb coated on the backwall of a Nb SRF cavity. This paper describes the setup of the experiment and first results from beam measurements.
Date: September 1, 2011
Creator: Kamps, T; Barday, R; Jankowiak, A; Knobloch, J; Kugeler, O; Matveenko, A N et al.
Partner: UNT Libraries Government Documents Department

High-Average Power Facilities

Description: There has been significant progress in the development of high-power facilities in recent years yet major challenges remain. The task of WG4 was to identify which facilities were capable of addressing the outstanding R&D issues presently preventing high-power operation. To this end, information from each of the facilities represented at the workshop was tabulated and the results are presented herein. A brief description of the major challenges is given, but the detailed elaboration can be found in the other three working group summaries.
Date: September 5, 2012
Creator: Dowell, David H.; /SLAC; Power, John G. & /Argonne
Partner: UNT Libraries Government Documents Department

Secondary-electron emission from hydrogen-terminated diamond

Description: Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in the vacuum level due to the Schottky effect. We demonstrated that the decrease in the secondary electrons average emission gain was a function of the pulse width and related this to the trapping of electrons by the effective NEA surface. The findings from the model agree well with our experimental measurements. As an application of the model, the energy spread of secondary electrons inside the diamond was estimated from the measured emission.
Date: May 20, 2012
Creator: E., Wang; Ben-Zvi, I.; Rao, T.; Wu, Q.; Dimitrov, D.A. & T. Xin, T.
Partner: UNT Libraries Government Documents Department

Emittance exchange results

Description: The promise of next-generation light sources depends on the availability of ultra-low emittance electron sources. One method of producing low transverse emittance beams is to generate a low longitudinal emittance beam and exchange it with a large transverse emittance. Experiments are underway at Fermilab's A0 Photoinjector and ANL's Argonne Wakefield Accelerator using the exchange scheme of Kim and Sessler. The experiment at the A0 Photoinjector exchanges a large longitudinal emittance with a small transverse emittance. AWA expects to exchange a large transverse emittance with a small longitudinal emittance. In this paper we discuss recent results at A0 and AWA and future plans for these experiments.
Date: September 1, 2009
Creator: Fliller, R.P., III; /Brookhaven; Koeth, T. & /Rutgers U., Piscataway
Partner: UNT Libraries Government Documents Department

Proposal for a High-Brightness Pulsed Electron Source

Description: We propose a novel scheme for a high-brightness pulsed electron source, which has the potential for many useful applications in electron microscopy, inverse photo-emission, low energy electron scattering experiments, and electron holography. A description of the proposed scheme is presented.
Date: October 16, 2006
Creator: Zolotorev, M.; Commins, E.D.; Heifets, S.; Sannibale, F. & /LBL, Berkeley /UC, Berkeley /SLAC
Partner: UNT Libraries Government Documents Department

Observation of transverse space charge effects in a multi-beamlet electron bunch produced in a photo-emission electron source

Description: A 'multiple beamlet' experiment aimed at investigating the transverse space charge effect was recently conducted at the Argonne Wakefield Accelerator. The experiment generated a symmetric pattern of 5 beamlets on the photocathode of the RF gun with the drive laser. We explored the evolution of the thereby produced 5 MeV, space-charge dominated electron beamlets in the 2m drift following the RF photocathode gun for various external focusing. Two important effects were observed and benchmarked using the particle-in-cell beam dynamics code IMPACT-T. In this paper, we present our experimental observation and their benchmarking with Impact-T.
Date: September 1, 2008
Creator: Rihaoui, M.; /Northern Illinois U. /NICADD, DeKalb; Gai, W.; /Argonne; Piot, P.; /Northern Illinois U. /NICADD, DeKalb /FERMILAB et al.
Partner: UNT Libraries Government Documents Department

DIAMOND SECONDARY EMITTER

Description: We present the design and experimental progress on the diamond secondary emitter as an electron source for high average power injectors. The design criteria for average currents up to 1 A and charge up to 20 nC are established. Secondary Electron Yield (SEY) exceeding 200 in transmission mode and 50 in emission mode have been measured. Preliminary results on the design and fabrication of the self contained capsule with primary electron source and secondary electron emitter will also be presented.
Date: October 9, 2005
Creator: BEN-ZVI, I.; RAO, T.; BURRILL, A.; CHANG, X.; GRIMES, J.; RANK, J. et al.
Partner: UNT Libraries Government Documents Department

Manipulation of the longitudinal profile

Description: We present studies of transverse emittances and electron beam pulse length for various operating points of the electron source: electron beam charge, laser length and spot size, and solenoid settings.We especially study the impact, on transverse emittance, of short Gaussian versus long square temporal distributions of the photocathode drive-laser.
Date: January 1, 2006
Creator: Tikhoplav, R.; /UCLA; Kazakevich, G.; /Fermilab; Mihalcea, D.; Piot, P. et al.
Partner: UNT Libraries Government Documents Department

The polarized electron beam for the SLAC Linear Collider

Description: The SLAC Linear Collider has been colliding a polarized electron beam with an unpolarized positron beam at the Z{sup 0} resonance for the SLD experiment since 1992. An electron beam polarization of close to 80% has been achieved for the experiment at luminosities up to 8 {center_dot} 10{sup 29} cm{sup {minus}2} s{sup {minus}1}. This is the world`s first and only linear collider, and is a successful prototype for the next generation of high energy electron linear colliders. This paper discusses polarized beam operation for the SLC, and includes aspects of the polarized source, spin transport and polarimetry.
Date: October 1, 1996
Creator: Woods, M.
Partner: UNT Libraries Government Documents Department

High voltage high brightness electron accelerator with MITL voltage adder coupled to foilless diode

Description: The design and analysis of a high brightness electron beam experiment under construction at Sandia National Laboratory is presented. The beam energy is 12 MeV, the current 35-40 kA, the rms radius 0.5 mm, and the pulse duration FWHM 40 ns. The accelerator is SABRE a pulsed inductive voltage adder, and the electron source is a magnetically immersed foilless diode. This experiment has as its goal to stretch the technology to the edge and produce the highest possible electron current in a submillimeter radius beam.
Date: December 31, 1995
Creator: Mazarakis, M.G.; Poulkey, J.W. & Rovang, D.
Partner: UNT Libraries Government Documents Department

A polarized photoluminescence study of strained layer GaAs photocathodes

Description: Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to {approximately}0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, {approx}78 K and {approx}12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16{+-}.21 eV, b = -2.00{+-}.05 eV and d = -4.87{+-}.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data.
Date: July 1, 1996
Creator: Mair, R.A.
Partner: UNT Libraries Government Documents Department

Preparation of GaAs photocathodes at low temperature

Description: The preparation of an atomically clean surface is a necessary step in the formation of negative electron affinity (NEA) GaAs. Traditional methods to this end include cleaving, heat cleaning and epitaxial growth. Cleaving has the advantage of yielding a fresh surface after each cleave, but is limited to small areas and is not suitable for specialized structures. Heat cleaning is both simple and highly successful, so it is used as a preparation method in virtually all laboratories employing a NEA source on a regular basis. Due to its high cost and complexity, epitaxial growth of GaAs with subsequent in vacuo transfer is not a practical solution for most end users of GaAs as a NEA electron source. While simple, the heating cleaning process has a number of disadvantages. Here, a variety of cleaning techniques related to preparation of an atomically clean GaAs surface without heating to 600 C are discussed and evaluated.
Date: October 1, 1996
Creator: Mulhollan, G.; Clendenin, J. & Tang, H.
Partner: UNT Libraries Government Documents Department

Polarization and charge limit studies of strained GaAs photocathodes

Description: This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of {approximately} 2.5 A/cm{sup 2} at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don`t have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes.
Date: March 1, 1997
Creator: Saez, P.J.
Partner: UNT Libraries Government Documents Department

Emittance studies of the BNL/SLAC/UCLA 1.6 cell photocathode rf gun

Description: The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 {micro}s. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, {epsilon}{sub o}, of the copper cathode has been measured.
Date: July 1997
Creator: Palmer, D. T.; Miller, R. H. & Wang, X. J.
Partner: UNT Libraries Government Documents Department

The SLAC polarized electron source

Description: The SLAC polarized electron source employs a photocathode DC high voltage gun with a loadlock and a YAG pumped Ti:sapphire laser system for colliding beam experiments or a flash lamp pumped Ti:sapphire laser for fixed target experiments. It uses a thin, strained GaAs(100) photocathode, and is capable of producing a pulsed beam with a polarization of {ge}80% and a peak current exceeding 10 A. Its operating efficiency has reached 99%. The physics and technology of producing high polarization electron beams from a GaAs photocathode will be reviewed. The prospects of realizing a polarized electron source for future linear colliders will also be discussed.
Date: June 1, 1995
Creator: Tang, H.; Alley, R. & Frisch, J.
Partner: UNT Libraries Government Documents Department

Atomic hydrogen cleaning of semiconductor photocathodes

Description: Negative Electron Affinity (NEA) semiconductor photocathodes are widely used for the production of polarized electron beams, and are also useful for the production of high brightness electron beams which can be modulated at very high frequencies. Preparation of an atomically clean semiconductor surface is an essential step in the fabrication of a NEA photocathode. This cleaning step is difficult for certain semiconductors, such as the very thin materials which produce the highest beam polarization, and those which have tightly bound oxides and carbides. Using a small RF dissociation atomic hydrogen source, the authors have reproducibly cleaned GaAs wafers which have been only degreased prior to installation in vacuum. They have consistently prepared very high quantum efficiency photocathodes following atomic hydrogen cleaning. Details of their apparatus and most recent results are presented.
Date: June 1, 1997
Creator: Sinclair, C. K.; Poelker, B. M. & Price, J. S.
Partner: UNT Libraries Government Documents Department

Deposition of field emissions cathodes over large areas

Description: Field emission cathodes (FECs) with characteristics of cold emission, low voltage operation, high current density and microscopic size meet the requirements for an electron source for use in vacuum microelectronics. Deposition efforts have focused on evaporation techniques, as electron beam, to produce the size and shape of cathode required for efficient operation. After two decades of development, the convention for FEC synthesis involves coating with very high tolerances for thickness uniformity using a planetary substrate fixture and a long source-to-substrate distance. A further reduction in the operating voltage results by increasing the density of emitters through a reduction of cathode size and spacing. In addition, the objective of scaling the substrate size from small to large areas has compounded the manufacturing requirements to a point beyond that which is obtainable through modifications to the conventional FEC deposition process. We have been successful in a new alternative approach to design, assemble and operate a system that enables FEC synthesis over large areas through the control of deposition source divergence and step-and-repeat substrate handling.
Date: April 3, 1997
Creator: Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

High-field penning-malmberg trap: confinement properties and use in positron accumulation

Description: This dissertation reports on the development of the 60 kG cryogenic positron trap at Lawrence Livermore National Laboratory, and compares the trap`s confinement properties with other nonneutral plasma devices. The device is designed for the accumulation of up to 2{times}10{sup 9} positrons from a linear-accelerator source. This positron plasma could then be used in Bhabha scattering experiments. Initial efforts at time-of-flight accumulation of positrons from the accelerator show rapid ({approximately}100 ms) deconfinement, inconsistent with the long electron lifetimes. Several possible deconfinement mechanisms have been explored, including annihilation on residual gas, injection heating, rf noise from the accelerator, magnet field curvature, and stray fields. Detailed studies of electron confinement demonstrate that the empirical scaling law used to design the trap cannot be extrapolated into the parameter regime of this device. Several possible methods for overcoming these limitations are presented.
Date: September 1, 1997
Creator: Hartley, J.H.
Partner: UNT Libraries Government Documents Department

Beam charge and current neutralization of high-charge-state heavy ions

Description: High-charge-state heavy-ions may reduce the accelerator voltage and cost of heavy-ion inertial fusion drivers, if ways can be found to neutralize the space charge of the highly charged beam ions as they are focused to a target in a fusion chamber. Using 2-D Particle-In- Cell simulations, we have evaluated the effectiveness of two different methods of beam neutralization: (1) by redistribution of beam charge in a larger diameter, preformed plasma in the chamber, and (2), by introducing a cold-electron-emitting source within the beam channel at the beam entrance into the chamber. We find the latter method to be much more effective for high-charge-state ions.
Date: October 29, 1997
Creator: Logan, B.G. & Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Simulations of the BNL/SLAC/UCLA 1.6 cell emittance compensated photocathode RF gun low energy beam line

Description: A dedicated low energy (2 to 10 MeV) experimental beam line is now under construction at Brookhaven National Laboratories Accelerator Test Facility (BNL/ATF) for photocathode RF gun testing and photoemission experiments. The design of the experimental line, using the 1.6 cell photocathode RF gun developed by the BNL/SLAC/UCLA RF gun collaboration is presented. Detailed beam dynamics simulations were performed for the 1.6 cell RF gun injector using a solenoidal emittance compensation technique. An experimental program for testing the 1.6 cell RF gun is presented. This program includes beam loading caused by dark current, higher order mode field measurements, integrated and slice emittance measurements using a pepper-pot and RF kicker cavity.
Date: June 1995
Creator: Palmer, D. T.; Miller, R. H.; Winick, H.; Wang, X. J.; Batchelor, K.; Woodle, M. et al.
Partner: UNT Libraries Government Documents Department