The present invention relates to high-performance accelerator systems and more specifically to a method for preparing a niobium surface with a nano-structure to produce a high quantum efficiency superconducting niobium surface.
Radio frequency photocathode electron guns are the source of choice for most high-performance accelerator systems. The main reason for this popularity is their ability to produce very bright beams of electrons. However, due to inherent limitations, photocathode radio frequency electron guns have not successfully penetrated certain key applications. One of these limitations is their inability to economically produce the high average current, high brightness electron beams necessary for certain applications. Another drawback is that one must choose between high quantum efficiency and durability. Durable cathodes tend to have relatively low quantum-efficiency, while high quantum efficiency cathode materials are very sensitive to vacuum conditions.
Superconducting Radio Frequency injectors are highly sought after for high brightness, high duty factor electron sources. The major hurdle in its development is the lack of a suitable photocathode that has high quantum efficiency, long life time and is compatible with the superconductivity of the injector.
Although generation of electrons from metals using multiphoton photoemission by use of nanostructured plasmonic surfaces has been reported for copper and aluminum, these structures are not suitable for forming fully superconducting radio frequency injectors. Furthermore, the aluminium nanostructures are grooves which unfortunately are sensitive to the polarization of the laser.
Accordingly, it would be desirable to provide a photocathode that has high quantum efficiency, long life time, and is compatible with a superconducting radio frequency injector.
A first object of the invention is to provide a photocathode for use in a superconducting radio frequency injector.
A second object of the invention is to provide a photocathode with a superconducting surface for use in superconducting high-performance accelerator systems.
A further object of the invention is to provide a method for increasing the effective quantum efficiency of a niobium surface by improving laser absorption and enhancing the local electric field.
A further object of the invention is to improve the feasibility of constructing superconducting radio frequency injectors with niobium as the photocathode.
A further object of the invention is to provide a superconducting nano-structured surface that is not dependent on laser polarization.
A further object of the invention is to improve the multi-photon emission process for extracting electrons from a photocathode surface.
Further advantages of the invention will be apparent from the following detailed description of illustrative embodiments thereof.
The present invention is a method for providing a superconducting surface on a laser-driven niobium cathode in order to increase the effective quantum efficiency. The enhanced surface increases the effective quantum efficiency by improving the laser absorption of the surface and enhancing the local electric field. The surface preparation method makes feasible the construction of superconducting radio frequency injectors with niobium as the photocathode. An array of nano-structures are provided on a flat surface of niobium. The nano-structures are dimensionally tailored to interact with a laser of specific wavelength to thereby increase the electron yield of the surface.
The present invention is a method for preparing a niobium photocathode surface with a nano-patterned structure to produce a high quantum efficiency superconducting surface.
Referring to
In forming the nano-holes at ambient temperature, the contraction of niobium at low temperatures is factored in such that the dimensions of the nano-holes are optimized for the niobium surface when it is in a superconducting state.
The nano-patterned surface greatly increases the absorption of laser light so that more photons will contribute to the photo-emission process. Additionally, as shown in
With reference to
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The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments herein were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
This invention was made with government support under Management and Operating Contract No. DE-AC05-06OR23177 awarded by the Department of Energy. The United States Government has certain rights in the invention.
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