Download or read book Photocathode Performance Measurements for the SLC Polarized Electron Gun written by and published by . This book was released on 1993 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: A low-voltage test system is used to qualify various III-V semiconductor materials as photocathodes for the SLC. The system features a load lock to introduce samples, high pumping speed, a sensitive residual gas analyzer, and an infrared temperature detector. Heat cleaning, cesiation, and oxidation procedures have been studied to optimize cathode activation for achieving an optimum NEA surface. VGF GaAs, MBE-grown AlGaAs, MBE GaAs layered on AlGaAs, and MOCVD GaAsP cathodes with different active layer thicknesses and doping concentrations have been tested for quantum efficiency and lifetime. New higher-polarization strained-layer GaAs on GaAsP photocathodes have also been tested. Results and operational experience are discussed.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-03 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advanced Strained Superlattice Photocathodes for Polarized Electron Sources written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Polarized electrons have been essential for high-energy parity-violating experiments and measurements of the nucleon spin structure. The availability of a polarized electron beam was crucial to the success of the Stanford Linear Collider (SLC) in achieving a precise measurement of the electroweak mixing angle, and polarized electron beams will be required for all future linear colliders. Polarized electrons are readily produced by GaAs photocathode sources. When a circularly polarized laser beam tuned to the bandgap minimum is directed to the negative-electron-affinity (NEA) surface of a GaAs crystal, longitudinally polarized electrons are emitted into vacuum. The electron polarization is easily reversed by reversing the laser polarization. The important properties of these photocathodes for accelerator applications are: degree of polarization of the extracted beam; ability to extract sufficient charge to meet accelerator pulse-structure requirements; efficiency and stability of operation; and absence of any asymmetries in the beam properties (charge, position, energy, etc.) upon polarization reversal. The performance of GaAs photocathodes has improved significantly since they were first introduced in 1978 [1]. The theoretical maximum polarization of 50% for natural GaAs was first exceeded in 1991 using the lattice mismatch of a thin InGaAs layer epitaxially grown over a GaAs substrate to generate a strain in the former that broke the natural degeneracy between the heavy- and light-hole valence bands [2]. Polarizations as high as 78% were produced for the SLC from photocathodes based on a thin GaAs epilayer grown on GaAsP [3,4]. After 10 years of experience with many cathode samples at several laboratories [5], the maximum polarization using the GaAs/GaAsP single strained-layer cathode remained limited to 80%, while the quantum efficiency (QE) for a 100-nm epilayer is only 0.3% or less. Two factors were known to limit the polarization of these cathodes: (1) the limited band splitting; and (2) a relaxation of the strain in the epilayer since the 10-nm critical thickness for maintaining perfect strain is exceeded for a 1 % lattice-mismatch [6]. Strained superlattice structures, consisting of very thin quantum well layers alternating with lattice-mismatched barrier layers are excellent candidates for higher polarization. Due to the difference in the effective mass of the heavy- and light-holes, a superlattice exhibits a natural splitting of the valence band, which adds to the strain-induced splitting. In addition, each of the SL layers is thinner than the critical thickness. Polarized photoemission from strained InGaAs/GaAs [7], InGaAdAlGaAs [8], and GaAs/GaAsP [9,10] superlattice structures have been reported in the literature. For this Phase II program, SVT Associates worked with the Stanford Linear Accelerator Center (SLAC) and University of Wisconsin at Madison to create photocathodes with improved polarization by employing GaAs/GaAsP superlattices. These superlattices consist of alternating thin layers of GaAs and GaAsP. The thicknesses and alloy compositions are designed to create a strained GaAs photoemission layer. Under strain, the heavy-hole and light-hole valence bands in GaAs split, removing degeneracy and allowing high polarization, theoretically 100%. This final report discusses the efforts and results achieved, comparing the device performance of newly created superlattice photocathodes grown by molecular beam epitaxy (MBE) with the devices created by other fabrication technologies, and efforts to optimize and improve the device operation.
Download or read book Proceedings of the 1993 Particle Accelerator Conference written by and published by . This book was released on 1993 with total page 888 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings of the Workshop on Photocathodes for Polarized Electron Sources for Accelerators Revision written by and published by . This book was released on 1994 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: Application of the GaAs polarized electron source to studies of surface magnetism; thermal stability of Cs on NES III-V-Photocathodes and its effect on quantum efficiency; AFEL accelerator; production and detection of SPIN polarized electrons; emittance measurements on a 100-keV beam from a GaAs photocathode electron gun; modern theory of photoemission and its applications to practical photocathodes; experimental studies of the charge limit phenomenon in GaAs photocathodes; new material for photoemission electron source; semiconductor alloy InGaAsP grown on GaAs substrate; NEA photocathode surface preparation; technology and physics; metalorganic chemical vapor deposition of GaAs-GaAsP spin-polarized photocathodes; development of photocathodes injectors for JLC-ATF; effect of radiation trapping on polarization of photoelectrons from semiconductors; and energy analysis of electrons emitted by a semiconductor photocathode.
Download or read book EPAC 92 written by H. Henke and published by Atlantica Séguier Frontières. This book was released on 1992 with total page 942 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High Energy Physics Index written by and published by . This book was released on 1993 with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High Voltage Processing of the SLC Polarized Electron Gun written by and published by . This book was released on 1993 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: The SLC polarized electron gun operates at 120 kV with very low dark current to maintain the ultra high vacuum (UHV). This strict requirement protects the extremely sensitive photocathode from contaminants caused by high voltage (HV) activity. Thorough HV processing is thus required x-ray sensitive photographic film, a nanoammeter in series with gun power supply, a radiation meter, a sensitive residual gas analyzer and surface x-ray spectrometry were used to study areas in the gun where HV activity occurred. By reducing the electric field gradients, carefully preparing the HV surfaces and adhering to very strict clean assembly procedures, we found it possible to process the gun so as to reduce both the dark current at operating voltage and the probability of HV discharge. These HV preparation and processing techniques are described.
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 Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 892 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Beam Line written by and published by . This book was released on 1992 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Annual Index written by and published by . This book was released on 1994 with total page 1224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Announcements Index written by and published by . This book was released on 1994 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Polarized Light Sources for Photocathode Electron Guns at SLAC written by and published by . This book was released on 1992 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: We describe current and future Polarized Light Sources at SLAC for use with photocathode electron guns to produce polarized electron beams. The SLAC experiments SLD and E142 are considered, and are used to define the required parameters for the Polarized Light Sources.
Download or read book Fermilab Meeting Dpf 92 The Proceedings Of The 7th Meeting Of The Aps Division Of Particles And Fields In 2 Volumes written by C H Albright and published by World Scientific. This book was released on 1993-06-01 with total page 1955 pages. Available in PDF, EPUB and Kindle. Book excerpt: These proceedings cover the latest results in Tevatron Collider Physics, LEP results, and results from other High Energy Physics Laboratories. The volume will consist of plenary and parallel contributions on the following subjects: Heavy Quark Physics, Physics Beyond the Standard Model, Astrophysics and Non-Accelerator Physics.
Download or read book International Linear Collider Technical Review Committee Second Report 2003 written by International Linear Collider Technical Review Committee and published by . This book was released on 2003 with total page 534 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigations of the Physical Properties of Photoemission Polarized Electron Sources for Accelerator Applications written by Bruce Matthew Dunham and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This experiment measured the polarization and quantum efficiency as a function of wavelength for the chalcopyrite semiconductor Zn(Ge$rmsb{0.7}Sisb{0.3})Assb2.$ Also, the onset of space charge growth of a 100 keV electron beam passing through the Illinois/CEBAF polarized electron injection system was studied by measuring the beam emittance as a function of current. Finally, the thermal properties of GaAs were investigated by measuring the beam emittance as functions of the excitation laser wavelength and the laser spot size. The experiments were performed at the University of Illinois Nuclear Physics Laboratory using a 100 keV photoemission polarized electron gun, a electron spin manipulation system of a novel design, a Mott polarimeter, and an emittance measuring system. The design and performance of the entire system is described. The maximum polarization of Zn(Ge$rm sb{0.7}Sisb{0.3})Assb2$ was measured to be $sim$19%, much lower than the expected 100%. Also, the expected transition of the polarization through zero was not observed. The beam emittance as a function of current was measured and the onset of space charge effects was found to be $sim$0.5 mA, much lower than predicted by the electron gun design program scEGUN. Finally, the effective transverse thermal energy of the electrons emitted from GaAs at 100 keV as a function of excitation wavelength was measured by a new method for low beam currents. The electron thermal energy for wavelengths between 840 and 633 nm was found to be $sim$33 meV, a factor of 3 lower than for a thermionic electron gun. It was also found to increase sharply for photon wavelengths less than 633 nm.
