Download or read book A Polarization Study of Strained GaAs Photocathode Structures written by and published by . This book was released on 1996 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The polarized electron source at SLAC has performed extremely well during recent years supplying electrons having a spin polarization of 78% (85%) for high (low) current operation with beam current limited primarily by experimental requirements. However, there is room for improvement in the electron polarization. The less-than-ideal polarizations are a result of both imperfections and depolarizing mechanisms within the photocathode. The structure of the photocathode used at SLAC in the polarized electron source is a single-strained emitting layer structure grown atop a GaAs substrate. Here, the properties of several types of strained GaAs and GaAsP photocathodes have been studied using x-ray diffraction and photoemission.
Download or read book A Polarized Photoluminescence Study of Strained Layer GaAs Photocathodes written by Robin Alexander Mair and published by . This book was released on 1996 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Polarized Photoluminescence Study of Strained Layer GaAs Photocathodes written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Spin 96 Proceedings Of The 12th International Symposium On High energy Spin Physics written by J E J Oberski and published by World Scientific. This book was released on 1997-04-15 with total page 906 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments using highly polarized intense beams and targets, and theoretical studies of spin and polarization phenomena, are now providing us with numerous additional details of the electroweak and strong interactions and the structure of matter. The spin structure of the nucleon has been measured over wide ranges of kinematic variables, and the cross sections have been calculated to several orders in perturbative field theory. At present, the influence of the higher twist contributions, the gluon spin, and the quark orbital angular momentum are under scrutiny. Quantum chromodynamics (QCD) captures a lot of our experimental knowledge of hard polarized scattering processes. Can our understanding of such processes within QCD be further improved?Hyperons produced in high energy reactions show how puzzling strong interactions between hadrons still are. Spin observables in experiments at intermediate energy are used to test parity and charge symmetries. Will they also reveal, at low energy, a violation of time reversal symmetry? We are on the verge of using parity violation measurements at intermediate electron scattering energies to determine the amount of strange quark contributions to the neutral weak form factor of the nucleon. The polarization of the sea quarks is expected to be measured soon in W± decays produced in high energy polarized proton interactions. Will the jets in polarized Z⁰ decays show a definite handedness? These and many other topics are discussed in these proceedings.
Download or read book Highly Polarized Electron Emission from Strain Compensated AlInGaAs GaAsP Superlattices written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: New results from experimental and theoretical studies of spin-polarized electron emission from InAlGaAs-GaAsP superlattice photocathodes with opposite strain in the quantum well and barrier layers are presented. The measured values of maximum polarization and quantum yield for the structure with a 0.18 [mu]m-thick working layer are close to the best results reported for strained superlattice photocathode structures, demonstrating the high potential of strain compensation for future photocathode applications. An analysis of the photoemission spectra is used to estimate the parameters responsible for the polarization losses.
Download or read book Polarization Possibilities of Small Spin Orbit Interaction in Strained Superlattice Photocathodes written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important. The strained-superlattice structure based on GaAsP/GaAs, with a maximum polarization as high as 90% and more than 1% quantum efficiency, is presently the prime candidate for the ILC polarized electron photocathodes. A recent systematic study shows, however, that the peak polarization seems saturated even though the heavy-hole (HH) and light-hole (LH) band splitting is increased significantly, indicating that there is a material specific spin relaxation mechanism. It is widely accepted that the D'yakonov-Perel mechanism is the dominant spin relaxation mechanism in the III-V compound superlattice structures with a low p-doping ((less-than or equal to) 1017 cm−3), and that the spin relaxation may be reduced by choosing a material with a smaller spin-orbit interaction. As the spin-orbit interaction in phosphides is much smaller than in arsenides, strained-superlattice structure based on InGaP/GaAs were investigated. The computer code SPECCODE developed by Subashiev and Gerchikov has been used for calculating the band structures in superlattice.
Download or read book Polarized Beam Dynamics and Instrumentation in Particle Accelerators written by François Méot and published by Springer Nature. This book was released on 2023-03-21 with total page 419 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Open Access book is drawn from lectures dispensed at the U.S. Particle Accelerator School (USPAS) Summer 2021 Spin Class, by experts in the field. It is an introduction to the dynamics of spin in charged particle accelerators, and to the accelerator components and spin manipulation techniques, including helical snakes and spin rotators, which enable and allow preserving beam polarization. It is aimed at graduate students or upper division undergraduate students with an interest in this multi-disciplinary field, which includes the future electron-ion collider at the Brookhaven National Laboratory, high energy lepton and proton collider projects, and other electric dipole moment search storage rings. It is also aimed at physicists or engineers working in accelerator-related fields who wish to familiarize themselves with spin dynamics and polarized beam concepts, tools, components, and purposes. This is an open access book.
Download or read book High Energy Accelerators Heacc 92 Proceedings Of The Xv International Conference In 2 Volumes written by J Rossbach and published by World Scientific. This book was released on 1993-02-10 with total page 1288 pages. Available in PDF, EPUB and Kindle. Book excerpt: The High Energy Accelerator Conference has always been the monitor of the state of the art and the new trends in planning, construction and operation of large particle accelerators. It is held every three years. The 1992 conference is devoted to High Energy Hadron Accelerators and Colliders, Linear Colliders, e⁺e⁻ Storage Rings and related Technologies for these machines. In addition to status reports and contributed papers, the program features twelve survey talks which include summaries of individual poster papers.
Download or read book InP and Related Compounds written by M O Manasreh and published by CRC Press. This book was released on 2000-08-08 with total page 862 pages. Available in PDF, EPUB and Kindle. Book excerpt: InP is a key semiconductor for the production of optoelectronic and photonic devices. Its related compounds, such as InGaAsP alloy, have been realized as very important materials for communication in the 1.3 and 1.55 micron spectral regions. Furthermore, the applications on InP and related compounds have extended to other areas that include laser d
Download or read book In Memory Of Vernon Willard Hughes Proceedings Of The Memorial Symposium In Honor Of Vernon Willard Hughes written by Emlyn Willard Hughes and published by World Scientific. This book was released on 2004-12-22 with total page 263 pages. Available in PDF, EPUB and Kindle. Book excerpt: On March 25, 2003 Professor Vernon Hughes of Yale University passed away in New Haven, Connecticut. His career in physics extended over more than 50 years, and his highly influential research work contributed invaluably to numerous fundamental questions in physics.This book comprises a compilation of articles covering talks given at the Vernon Willard Hughes Memorial Symposium, which took place at Yale University in November 2003. The fascinating contributions from many leading experimental and theoretical physicists cover topics in atomic, nuclear and particle physics, as well as include remarks made by Professor Alan Bromley at the symposium dinner. The book also features the Biographical Memoirs of Professor Hughes, written by Professor Robert Adair for the US National Academy of Sciences, and a complete list of Professor Hughes's publications.The proceedings have been selected for coverage in:• Index to Scientific & Technical Proceedings® (ISTP® / ISI Proceedings)• Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings)• CC Proceedings — Engineering & Physical Sciences
Download or read book PSTP 2007 written by Ahovi Kponou and published by American Institute of Physics. This book was released on 2008-02-25 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: Upton, New York, 10-14 September 2007
Download or read book Modern Developments in Vacuum Electron Sources written by Georg Gaertner and published by Springer Nature. This book was released on 2020-10-09 with total page 609 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book gives an overview of modern cathodes and electron emitters for vacuum tubes and vacuum electron devices in general. It covers the latest developments in field emission theory as well as new methods towards improving thermionic and cold cathodes. It addresses thermionic cathodes, such as oxide cathodes, impregnated and scandate cathodes, as well as photocathodes and field emitters – the latter comprising carbon nanotubes, graphene and Spindt-type emitter arrays. Despite the rise and fall of the once dominant types of vacuum tubes, such as radio valves and cathode ray tubes, cathodes are continually being improved upon as new applications with increased demands arise, for example in electron beam lithography, high-power and high-frequency microwave tubes, terahertz imaging and electron sources for accelerators. Written by 17 experts in the field, the book presents the latest developments in cathodes needed for these applications, discussing the state of the art and addressing future trends.
Download or read book Unifying Physics of Accelerators Lasers and Plasma written by Andrei Seryi and published by CRC Press. This book was released on 2023-04-30 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: Unifying Physics of Accelerators, Lasers and Plasma introduces the physics of accelerators, lasers and plasma in tandem with the industrial methodology of inventiveness, a technique that teaches that similar problems and solutions appear again and again in seemingly dissimilar disciplines. This unique approach builds bridges and enhances connections between the three aforementioned areas of physics that are essential for developing the next generation of accelerators. A Breakthrough by Design approach, introduced in the book as an amalgam of TRIZ inventive principles and laws of technical system evolution with the art of back-of-the-envelope estimations, via numerous examples and exercises discussed in the solution manual, will make you destined to invent. Unifying Physics of Accelerators, Lasers and Plasma outlines a path from idea to practical implementation of scientific and technological innovation. This second edition has been updated throughout, with new content on superconducting technology, energy recovery, polarization, various topics of advanced technology, etc., making it relevant for the Electron-Ion Collider project, as well as for advanced lights sources, including Free Electron Lasers with energy recovery. The book is suitable for students at the senior undergraduate and graduate levels, as well as for scientists and engineers interested in enhancing their abilities to work successfully on the development of the next generation of facilities, devices and scientific instruments manufactured from the synergy of accelerators, lasers and plasma. Key Features: Introduces the physics of accelerators, lasers, and plasma in tandem with the industrial methodology of inventiveness. Outlines a path from idea to practical implementation of scientific and technological innovation. Contains more than 380 illustrations and numerous end-of-chapter exercises. Solutions manual is included into the book. Boasting more than 380 illustrations, this highly visual text: Employs TRIZ to amalgamate and link different areas of science Avoids heavy mathematics, using back-of-the-envelope calculations to convey key principles Introduces the Innovation by Design approach based an amalgam of TRIZ inventive principles and laws of technical system evolution with the art of back-of-the-envelope estimations – developing and applying this methodology, you will be destined to invent Includes updated materials for all eleven chapters of the first edition, e.g., the FEL invention path analysis, etc. The second edition includes new chapters: Beam Cooling and Final Focusing, Beam Stability and Energy Recovery, Advanced Technologies The new chapters add topics such as superconducting magnets and accelerating cavities, polarized beams, energy recovery – themes relevant for new projects such as Electron-Ion Collider, or Free Electron Laser based on energy recovery for science or industry The second edition also includes a new chapter with illustrations of 40 inventive principles of TRIZ based on the areas of accelerator, laser and plasma technology Every chapter includes invention case studies, often making important connections to adjacent areas of technologies, illustrated by the case of EUV light generation invention for semiconductor lithography, etc. Includes end-of-chapter exercises focusing on physics and on applications of the inventiveness method, on reinventing technical systems and on practicing back-of-the-envelope estimations; and also includes mini-projects, suitable for exercises by teams of students Includes a detailed Guide to solutions of the exercises, discussing the inventions and highlighting the relevant inventive principles, as well as directions of mini-projects Includes discussion of the TRIZ laws of evolution of technical systems and makes bold predictions for the Year 2050 for accelerator, laser and plasma technology Praise for the first edition "...Unifying Physics of Accelerators, Lasers and Plasma is a must-have for every student and practitioner of accelerator science. It is a quick reference guide and provides solid, intuitive discussions of what are often quite erudite concepts. I enthusiastically applaud this outstanding book." Sekazi Mtingwa in Physics Today, August 2016
Download or read book Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.
Download or read book Proceedings of the 11th International Workshop on Polarized Sources and Targets written by Tomohiro Uesaka and published by World Scientific. This book was released on 2007 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polarized beams and targets have been irreplaceable tools in nuclear and particle physics experiments for a long time and have provided us rich information on the role played by spin-degrees of freedom in the sub-nuclear world. In addition, techniques to obtain large nuclear polarization have recently been applied to new fields such as materials and medical sciences.The scope of these proceedings covers recent progress of state-of-the-art techniques in spin polarization, the cryogenic method, the atomic beam method, the optical pumping method and the nuclear reaction method.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2002 pages. Available in PDF, EPUB and Kindle. Book excerpt:
