摘要:

This paper discusses perspectives for a future fixed‐target electron‐nucleon scattering facility in Europe. Based on the intended measurements the requirements on accelerator, target and spectrometer are presented and their possible realisation is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607281

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In the last several years, the realization of an Electron‐Ion Collider (EIC) with luminosity greater than 1033cm− 2s− 1, a center‐of‐mass energy in the range of 30 to 100 GeV and employing spin‐polarized electron and nucleon beams as well as beams of low mass to heavy ions has developed into a leading initiative in hadronic physics worldwide. Using the precisely determined electroweak interaction to probe hadronic matter, EIC would open a new window on the fundamental quark and gluon structure of the nucleon and address completely new aspects of hadron structure like the origin of nuclear binding and the search for highly saturated gluonic matter. A promising realization of EIC utilizes the existing Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, New York, USA which has accelerated both heavy ions as well as polarized protons. At present, an effort is underway to develop a conceptual design for an electron‐ion collider using RHIC within the next several years. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607282

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The layout and main parameters of the e‐ring for EIC project are presented. Optics properties to fulfil so‐called spin‐transparency conditions to obtain sufficient polarization degree at IP are given. The possibility of using super‐bend magnets for polarization time in a wide energy range to decrease is also discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607283

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A spin‐dependent transport experiment in which hot electrons pass through a ferromagnetic metal / semiconductor Schottky diode has been performed. A spin‐polarized free‐electron beam, emitted in vacuum from a GaAs photocathode, is injected into the thin metal layer with an energy between 5 and 1000 eV above to the Fermi level. The transmitted current collected in the semiconductor substrate increases with injection energy because of secondary ‐ electron multiplication. The spin‐dependent part of the transmitted current is first constant up to about 100 eV and then increases by 4 orders of magnitude. As an immediate application, the solid‐state hybrid structure studied here leads to a very efficient and compact device for spin polarization detection. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607284

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

By varying of the phosphorous contents “x” and “y” at the GaAs1−xPx/GaAs1−yPycathodes they can be tuned to the wavelength, corresponding to maximum light power of the certain accelerator laser system. The parameters of strained GaAsP sample have been modified to enhance the quantum yield value at polarization maximum. The modification consisted of the incorporation of heavily doped thin GaAs quantum well layer at the top part of the structure. At the polarization maximum the yield enhancement of up to ten times has been achieved. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607285

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The polarization dependence of Compton scattering in magnetized iron can be used to determine the polarization of an incident photon beam. This can in turn be related to the polarization of the electron beam which radiated the photons. It is difficult to calculate the analyzing power of these devices absolutely, however they are of great utility for rapid, relative measurements of electron beam polarization. These devices have been used at Bates as relative electron polarization monitors at 20 and 200 MeV. Efforts are now being made to use the device at 850 MeV as an online measure of the beam polarization in the South Hall Ring. A technique to calibrate these devices and build an affordable, absolute polarimeter is also being explored. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607286

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The investigation of the photoelectron‐escape mechanism from GaAs cathodes with negative electron affinity requires the detection of very low energy electrons. We have built a novel, UHV‐compatible, spectrometer where the photoelectrons are imaged by a homogeneous electric field onto a position‐sensitive detector. The time‐of‐flight of each single emitted electron and its position on the detector is measured. From these informations energy‐distribution curves are extracted. The spectrometer has run successfully and preliminary energy‐distribution curves have been measured. The system is now under improvement. With the optimized spectrometer, an excellent energy resolution (a few meV) can be achieved. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607287

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Experiments with a polarized electron beam stored in the South Hall Ring (SHR) at MIT‐Bates Linear Accelerator Center will begin in 2003. Currently, the commissioning of BLAST detector is under way. The polarized injector uses for the first time high power diode array laser for photoemission. The laser operates at a wavelength of 808 nm and produces peak power up to 150 W at a duty factor of 1.5&percent;. Higher power is available at lower duty factor. The laser is coupled to a fiber, laser beam emitting from the fiber has an emittance of 200 mm⋅mrad and a set of lenses is used to deliver the beam through polarizing optics to a strained GaAs crystal inside the electron gun. The photocathode has a diameter of 11 mm and the laser illuminates the entire area. The gun optics has been specifically designed for such a large beam spot size. The diode laser provides an excellent stability and convenience of operation. At the same time, large divergence of the laser beam requires special attention to the transport system in general, and to polarizing optics in particular. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607288

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In 1998–2001 three series of SAMPLE experiment [1–3] were conducted at the MIT‐Bates Linear Accelerator Center. SAMPLE measures parity‐violating effects in electron scattering from protons and deuterons. The measured asymmetry associated with electron helicity is very small (about 1 ppm). In order to reduce systematic errors, the properties of the beam (intensity, position, size and energy) must remain unchanged when the helicity of polarized electrons is reversed. In this paper we analyze the sources of the helicity‐correlated effects in the electron beam and our approach to minimize them. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607289

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The SLAC high‐gradient‐doped MOCVD‐grown GaAs cathode presently in use consists of a strained GaAs low‐doped layer (with a small admixture of P) capped by a few nanometers of highly Zn‐doped GaAs, which is heat‐cleaned at relatively high temperature and then activated by Cs/NF3co‐deposition. The high‐gradient‐doped structure solves the problem of the surface charge limit that the previously‐used SLAC cathodes had, and this preparation procedure has produced satisfactory results. However, the preparation procedure has a few weaknesses that prevent cathodes from achieving the ultimate desired performance. The peak polarization is limited to 80&percent; due to strain relaxation in the relatively thick strained layers. Also dopant loss causes the surface charge limit effect to reappear after multiple high‐temperature heat‐cleanings. In this paper, we will discuss recent progress made at SLAC that addresses these limitations, including using the MBE growth technique with Be doping and using the superlattice structure. In addition, to reduce the heat‐cleaning temperature, an atomic hydrogen cleaning technique is explored. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607290

出版商:AIP    

年代:1903

数据来源: AIP