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07. December 2018

Photocathodes with high quantum efficiency for bERLinPro

A team at the HZB has improved the manufacturing process of photocathodes

Photocathode. Copyright: J. Kühn/HZB
Photocathode in superconducting photoinjector system. Copyright: J. Kühn/HZB

Teams from the accelerator physics and the SRF groups at HZB are developing a superconducting linear accelerator featuring energy recovery (Energy Recovery Linac) as part of the bERLinPro project. It accelerates an intense electron beam that can then be used for various applications – such as generating brilliant synchrotron radiation. After use, the electron bunches are directed back to the superconducting linear accelerator, where they release almost all their remaining energy. This energy is then available for accelerating new electron bunches.

Electron source: photocathode

A crucial component of the design is the electron source. Electrons are generated by illuminating a photocathode with a green laser beam. The quantum efficiency, as it is referred to, indicates how many electrons the photocathode material emits when illuminated at a certain laser wavelength and power. Bialkali antimonides exhibit particularly high quantum efficiency in the region of visible light. However, thin films of these materials are highly reactive and therefore very sensitive, so they only work at ultra-high vacuum.

Manufacturing process modified

A HZB team headed by Martin Schmeißer, Dr. Julius Kühn, Dr. Sonal Mistry, and Prof. Thorsten Kamps has now greatly improved the performance of the photocathode so it is ready for use with bERLinPro. They modified the manufacturing process for the photocathodes of cesium- potassium-antimonide on a molybdenum substrate. The new process delivers the desired high quantum efficiency and stability. Studies showed that the photocathodes do not degrade, even at low temperatures. This is a critical prerequisite for operation within a superconducting electron source, where the cathode must be operated at temperatures far below zero.

High quantum efficiency

The physicists were able to demonstrate this performance with detailed studies: Even after its transport via the photocathode transfer system and introduction into the photo injector of the SRF, the quantum efficiency of the photocathode was still about five times higher than necessary to achieve the maximum electron-beam current needed for bERLinPro.

Milestone for bERLinPro

“An important milestone for bERLinPro has been reached. We now have the photocathodes available to generate the first electron beam from our SRF photoinjector at bERLinPro in 2019“, says Prof. Andreas Jankowiak, head of the HZB Institute for Accelerator Physics.

  • More information on bERLinPro

Published in Physical Review Accelerators and Beams (2018):  Addressing challenges related to the operation of Cs-K-Sb photocathodes in SRF photoinjectors
M. A. H. Schmeisser, S. Mistry, H. Kirschner, S. Schubert, A. Jankowiak, T. Kamps, J. Kühn
doi: 10.1103/PhysRevAccelBeams.21.113401

 

Contact:

Helmholtz-Zentrum Berlin für Materialien und Energie
Institute Accelerator Physics

Dr. Julius Kühn
Tel.: (030) 8062-14784 / -13460
Email: julius.kuehn(at)helmholtz-berlin.de

Prof. Dr. Thorsten Kamps
Tel.: (030) 8062-15157
Email: kamps(at)helmholtz-berlin.de

Research Photonics / Optics Microsystems / Materials

Related News

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    HZB team generates and accelerates an electron beam from a multi-alkali photocathode
  • A look into the lab where the components of the electron source were tested.

    Milestone reached: electron source for bERLinPro produces its first beam

    Components for linear accelerator tested successfully
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The development of the Science and Technology Park Berlin Adlershof was and is co-financed by the European Union namely by EFRE. This concerns infrastructure development like construction of technology centres. Furthermore EFRE is used for international projects.

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