Ion (or electron) emitting sources based on the field emission effect, used for ground and space based applications, are usually implemented using a solid structure in the form of a capillary, a needle (solid or porous) and arrays of these elements. The process to manufacture such structures, however, is very expensive and complicated, and it is constituted by several steps: the creation of a mold, the powder injection molding process, and the electrochemical needle etching process. In particular, the last step is very difficult to implement in the case of 2D arrays.
Here we propose a novel method of producing dense arrays of needle-like structures using magnetically shaped metal powders. Upon the application of a magnetic field, ferromagnetic powders are subjected to instabilities which give rise to the formation of typical arrays of spikes. Depending on the size of the powder grains, the strength of the magnetic field, and few other parameters, it is possible to obtain various spike distributions and shapes, with tip sharpness high enough to be suitable for field emission devices (thus not requiring the additional step of electrochemical sharpening).
Preliminary activity on the subject has been already pursued at Fotec GmbH, consisting in the production of magnetically shaped arrays and in testing their behavior when impregnated with liquid metal and subjected to high voltages. These tests showcase very promising results. The goal of the proposed activity is to expand on those early results and produce a working ion thruster prototype, with the main aim to assess the capabilities, the durability and the robustness of the novel field emission device.
