CERN Accelerating science

European Organization for Nuclear Research

Reduction of SEY by magnetic roughness


There is a common problem in microwave systems of satellites and in particle accelerators, namely the multipactoring effect, a kind of electron resonance in powerful radiofrequency (RF) fields. This effect is strongly linked with the secondary electron yield (SEY) of metallic surfaces involved. To reduce SEY, the idea is to produce an electromagnetically rough surface which is mechanically very smooth. This electromagnetic roughness can be implemented by magnetizing the intermediate layer between the aluminum body of some (satellite) microwave filter and the final silver coating (RF losses). The coatings typically have a thickness of 10 µm. Magnetization can be done with a write head. This type of static magnetization pattern should have a similar effect on slow electrons close to the surface, but without is disadvantage of degrading RF losses.

Area of expertise

Surfaces and coatings, Radio frequency technology.


Space technology, satellites, many kinds of high power microwave tubes; in general all devices where considerable microwave and RF power is used in vacuum inside a metallic structure. The method can also be integrated into a satellite payload environment without violating any of the many rules about space and vacuum, material constraints etc. The same concept is applicable for particle accelerator components like (normal conducting) RF cavities and in particular to RF coupler structures (power coupler, HOM coupler) which are prone to multipactoring.


The technology, which requires a final experimental verification, would be extremely simple and cost effective and in particular nicely compatible with all the stringent requirements for satellite payloads, without showing drawbacks like increase of RF losses or long term stability issues of existing solutions. A modified version of this concept could also be used for reductions of SEY in accelerator beam pipes by producing a spatially rapidly changing modulation of the external magnetic field (bending magnets) by means of small ferromagnetic inclusions, grids or insertions. Those magnetostatic perturbations would be very local (just a few tens of µm) and not produce any significant magnetic field distortion seen by the beam. However, very minor and predictable field corrections may be required (corrections of bending magnet current).


The realization of the magnetization pattern in complex structures might lead to practical problems.
In certain cases (e.g. normal conducting accelerator cavities and couplers) the ferromagnetic layer is not foreseen a priori and would require an additional production step.

Intellectual Property status

Patent application filed.

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