In the case of very low emittance electron and positron storage ring beams, it is impossible to make intrusive measurements of beam properties without increasing the emittance and possibly disrupting the beam. In cases where electron or positron beams have high average power densities (such as free electron laser linacs), intrusive probes such as wires and optical transition radiation screens or Cherenkov emitting screens can be easily damaged or destroyed. The optical and x‐ray emissions from the bends in the storage rings and often from linac bending magnets can be used to image the beam profile to obtain emittance information about the beam. The techniques, advantages and limitations of using both optical and x‐ray synchrotron emission to measure beam properties are discussed and the possibility of single bunch imaging is considered. The properties of suitable imagers and converters such as phosphors are described. Examples of previous, existing and planned applications are given where available, inclu...

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Optical and x-ray imaging of electron beams using synchrotron emission

The Cambridge Electron Accelerator (CEA) has been devoted solely to electron-positron colliding-beam physics since 1970 By early 1972 an operational system had been developed with a peak luminosity of 2 × 1028cm-2sec-1 An experiment observing e+e- , ??, ?+ ?-, and hadron events was then completed at a beam energy of 2 + 2 GeV and an integrated luminosity of 112 x 1034cm-2 Since then, many improvements have been made to increase the average luminosity and to permit operation at higher energy A cryogenic pumping system has been installed close to the interaction region resulting in a significant pressure drop and reduction in background in the luminosity counters A final experiment is now in progress at a center-of-mass energy of 25 + 25 GeV, after which the colliding beam physics program will be terminated because higher luminosity is available from the Stanford storage ring SPEAR

Performance of the CEA as an e+e- Storage Ring

The physics and practical performance limits of various types of profile monitors are described. These devices essentially all detect the products of electromagnetic interactions of the particle beam with solid, gaseous or even liquid targets. These mechanisms can be more or less destructive to the beam. Low emittance and high luminosity beams have prompted improvements in resolution to 30 microns and below.

Beam profile measurements

Synchrotron light is routinely used in measuring the cross-section of a high-energy, orbiting, electron beam. The resolution of the height measurement is limited by the small vertical opening angle of this light. Because the angle decreases as a fractional power of decreasing wavelength, it is advantgeous to use a shorter wavelength portion of the synchrotron radiation, i.e., the x-ray portion. Accurate measurement of beam height is especially important to the CEA colliding beam program. A pinhole was installed in one of the tangential beam runs and the x-radiation image of the crosssection was recorded with a Polaroid x-ray cassette. A resolution of about 0.1 mm in beam height was obtained. The measured height of the stored beam was in agreement with expectation.

A. Hofmann

Papers

Measurement of Cross Section of a High-Energy Electron Beam by Means of the X-Ray Portion of the Synchrotron Radiation