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The Center for Bright Beams, A National Science Foundation Science and Technology Center

Beam Production

CBB aims to produce exceptionally bright electron beams using the process of photoemission. 

 

To do so, it starts by developing new insights into the physics of photoemission, and then uses those insights to design optimal photocathodes from the ground up. In a bright beam, the emitted electrons have very low mean transverse energy.  For some applications, a slow stream of electrons will suffice, while others require high electron flux and a photocathode that can survive in harsh conditions.

CBB targets specific Beam Production Objectives and Deliverables.

Theory – CBB is developing the theory of photoemission, including processes such as multi-electron emission, the scattering of the electrons at the surface due to roughness at the atomic scale, and the chemical structure of the surface. It is also understanding the processes used to grow photocathodes.

Growth – CBB grows smooth photocathodes using techniques such as molecular beam epitaxy.  By comparing observed behavior with theoretical predictions, it has identified the photocathode characteristics that drive its performance.  Now, CBB is using that knowledge to produce photocathodes that approach the ideal.

Characterization – CBB has invented instruments that can measure the properties of the beams produced by the photocathodes with unprecedented precision.  CBB chemists also examine the structure of photocathodes as part of improving growth procedures.

Tests – CBB puts its photocathodes to work in beamlines that are designed for applications such as ultrafast diffraction.   Besides advancing that technology, beam tests reveal their performance in real-life operating conditions.

Applications – CBB is working with scientists in national labs and industry in order to put its photocathodes to use in applications such as X-ray free-electron lasers and commercial electron microscopes.