摘要:

We have used a new configuration for a noble gas optical electron polarimeter. This polarimeter is part of an experiment involving dichroic scattering of longitudinally polarized electrons from chiral molecules. Our polarimeter sits along the electron beam axis at the end of the apparatus and measures the polarization of noble gas fluorescence emitted at 0°. The polarimeter is maximally sensitive to longitudinal electron polarization, and it maintains the axial symmetry of our experiment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607291

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Future colliders that require low‐emittance highly‐polarized electron beams are the main motivation for developing a polarized rf gun. However there are both technical and physics issues in generating highly polarized electron beams using rf guns that remain to be resolved. The PWT design offers promising features that may facilitate solutions to technical problems such as field emission and poor vacuum. Physics issues such as emission time now seem to be satisfactorily resolved. Other issues, such as the effect of magnetic fields at the cathode—both those associated with the rf field and those imposed by schemes to produce flat beams—are still open questions. Potential solution of remaining problems will be discussed in the context of the PWT design. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607292

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The SLAC PES, developed in the early 1990s for the SLC, has been in continuous use since 1992, during which time it has undergone numerous upgrades. The upgrades include improved cathodes with their matching laser systems, modified activation techniques and better diagnostics. The source itself and its performance with these upgrades will be described with special attention given to recent high‐intensity long‐pulse operation for the E‐158 fixed‐target parity‐violating experiment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607293

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

An ambitious nuclear physics research program continues at Jefferson Lab with Users at three experiment halls receiving reliable, highly polarized electrons at currents to 100 &mgr;A. The polarized photoguns and drive lasers that contribute to Jefferson Lab’s success will be described as well as significant events since PES2000. Typical of conditions at accelerators worldwide, success brings new challenges. Beam quality specifications continue to become more demanding as Users conduct more challenging experiments. In the months that follow this workshop, two parity violation experiments will begin at Jefferson Lab, G0 and HAPPEx2. The photogun requirements for these experiments will be discussed as well as our plans to eliminate/minimize systematic errors. Recent efforts to construct high power Ti‐Sapphire drive lasers for these experiments also will be discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607294

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

At the electron stretcher accelerator ELSA in Bonn a pulsed 50 kV inverted gun of polarized electrons has been in operation since February 2000. A strained‐layer superlattice crystal is used to deliver a beam with a polarization of about 80 &percent;. A flashlamp‐pumped Ti‐Sapphire laser with a pulse repetition rate of 50 Hz serves as source of light. The gun is operated in space charge limitation. The current can be chosen by varying the distance between cathode and anode. With 1 &mgr;s pulses of 100 mA the source was particularly used together with a polarized target for a GDH sum rule experiment. The high photocathode lifetime allows continuous operation at 100 mA typically for periods of about two weeks without maintenance. So far no change of the crystal was necessary. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607295

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The MIT‐Bates Compton Polarimeter, a laser back‐scattering device, is used to measure the polarization of electron beams circulating in the South Hall Ring for a range of energies between 300 and 1000 MeV. The apparatus is described in detail and compared to other polarimeters operating within a similar energy region. Preliminary polarization results at 850 MeV are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607296

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

200 keV polarized electron source with load‐lock system has been constructed to produce a beam with high peak current and low emittance that are required by a future linear collider. GaAs photocathode was cleaned by atomic hydrogen and dark currents between the electrodes of the gun that degrade an NEA (Negative Electron Affinity) surface of photocathode could be reduced to less than 1 nA at 200 kV. Recent data on photocathode preparation and dark current measurement are reported in this paper. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607297

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In order to produce the lower emittance electron beam, the higher field gradient must be used for the gun. From this point of view, we try to develop both of a polarized DC‐gun and RF‐gun. In case of a 200 keV polarized DC‐gun at Nagoya University, the accelerating gradient at the photocathode surface was designed to be 3 MV/m, and the dark current emitted from the SUS electrodes was suppressed below 1 nA. To increase the gradient, we tested the property of pure Titanium as a new electrode material. The tested electrode showed small dark current (∼1 nA) even at field gradient of 88 MV/m, which is as twice as higher than that of SUS electrode. Concerning the feasibility of a polarized RF‐gun, it seems difficult for the NEA surface to survive in high field gradient of 100 MV/m. Therefore, we proposed a new type of polarized electron source using two‐photon excitation method, for which it is not necessary to use the NEA surface to extract electrons into vacuum. For this method, the polarization higher than 90 &percent; was already demonstrated by the photoluminescence measurement using the bulk GaAs crystal. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607298

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Strained‐layer GaAs photocathodes are used at Jefferson Lab to obtain highly polarized electrons. Exposure to atomic hydrogen (or deuterium) is used to clean the wafer surface before the activation with cesium and nitrogen trifluoride to consistently produce high quantum yield photocathodes. The hydrogen‐cleaning method is easy, reliable and inexpensive. However, recent tests indicate that exposure to atomic hydrogen may affect the polarization of the electron beam. This paper presents preliminary results of a series of tests conducted to study the effect of atomic H exposure on the polarized electron beam from a strained‐layer GaAs sample. The experimental setup is described and the first measurements of the beam polarization as a function of exposure dose to atomic hydrogen are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607299

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A new 100 kV load locked polarized electron gun has been built at Jefferson Lab. The gun is installed in a test stand on a beam line that resembles the first few meters of the CEBAF nuclear physics photoinjector. With this gun, a GaAs photocathode can be loaded from atmosphere, hydrogen cleaned, activated and taken to high voltage in less than 8 hours. The gun is a three chamber design, with all of the moving parts remaining at ground potential during gun operation. Studies of gun performance, photocathode life times, transverse emittance at high bunch charge, helicity correlated effects and beam polarizations from new photocathode samples will all be greatly facilitated by the use of this load locked gun. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607300

出版商:AIP    

年代:1903

数据来源: AIP