Milestone for bERLinPro: photocathodes with high quantum efficiency

Photocathode in superconducting photoinjector system.

Photocathode in superconducting photoinjector system. © J. Kühn/HZB

The superconducting photoinjector system (1): The photocathode (3) is excited by a green laser (2) and emits electrons (4) which are accelerated in the superconducting RF cavity.

The superconducting photoinjector system (1): The photocathode (3) is excited by a green laser (2) and emits electrons (4) which are accelerated in the superconducting RF cavity. © Britta Mießen

Photocathode after its production in the preparatory system.

Photocathode after its production in the preparatory system. © J. Kühn/HZB

A team at the HZB has improved the manufacturing process of photocathodes and can now provide photocathodes with high quantum efficiency for bERLinPro.

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.

 

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

 

 

arö


You might also be interested in

  • Unconventional piezoelectricity in ferroelectric hafnia
    Science Highlight
    26.02.2024
    Unconventional piezoelectricity in ferroelectric hafnia
    Hafnium oxide thin films are a fascinating class of materials with robust ferroelectric properties in the nanometre range. While their ferroelectric behaviour is extensively studied, results on piezoelectric effects have so far remained mysterious. A new study now shows that the piezoelectricity in ferroelectric Hf0.5Zr0.5O2 thin films can be dynamically changed by electric field cycling. Another ground-breaking result is a possible occurrence of an intrinsic non-piezoelectric ferroelectric compound. These unconventional features in hafnia offer new options for use in microelectronics and information technology.
  • 14 parameters in one go: New instrument for optoelectronics
    Science Highlight
    21.02.2024
    14 parameters in one go: New instrument for optoelectronics
    An HZB physicist has developed a new method for the comprehensive characterisation of semiconductors in a single measurement. The "Constant Light-Induced Magneto-Transport (CLIMAT)" is based on the Hall effect and allows to record 14 different parameters of transport properties of negative and positive charge carriers. The method was tested now on twelve different semiconductor materials and will save valuable time in assessing new materials for optoelectronic applications such as solar cells.
  • Sodium-ion batteries: How doping works
    Science Highlight
    20.02.2024
    Sodium-ion batteries: How doping works
    Sodium-ion batteries still have a number of weaknesses that could be remedied by optimising the battery materials. One possibility is to dope the cathode material with foreign elements. A team from HZB and Humboldt-Universität zu Berlin has now investigated the effects of doping with Scandium and Magnesium. The scientists collected data at the X-ray sources BESSY II, PETRA III, and SOLARIS to get a complete picture and uncovered two competing mechanisms that determine the stability of the cathodes.