Editing Ion thruster (section)

=== Field-emission electric propulsion ===
{{main|Field-emission electric propulsion}}

[[Field-emission electric propulsion]] (FEEP) thrusters may use [[caesium]] or [[indium]] propellants. The design comprises a small propellant reservoir that stores the liquid metal, a narrow tube or a system of parallel plates that the liquid flows through and an accelerator (a ring or an elongated aperture in a metallic plate) about a millimeter past the tube end. Caesium and indium are used due to their high atomic weights, low ionization potentials and low melting points. Once the liquid metal reaches the end of the tube, an electric field applied between the emitter and the accelerator causes the liquid surface to deform into a series of protruding cusps, or ''[[Taylor cone]]s''. At a sufficiently high applied voltage, positive ions are extracted from the tips of the cones.<ref>{{cite web |title=FEEP – Field-Emission Electric Propulsion |url=http://www.alta-space.com/index.php?page=feep |url-status=dead |archive-url=https://web.archive.org/web/20120118051025/http://www.alta-space.com/index.php?page=feep |archive-date=2012-01-18 |access-date=2012-04-27}}</ref><ref name="JPP98">{{cite web|url=http://www.alta-space.com/uploads/file/publications/feep/Marcuccio-JPP14_5_1998.pdf|title=Experimental Performance of Field Emission Microthrusters|author=Marcuccio, S.|display-authors=etal|access-date=2012-04-27|url-status=dead|archive-url=https://web.archive.org/web/20130520151812/http://www.alta-space.com/uploads/file/publications/feep/Marcuccio-JPP14_5_1998.pdf|archive-date=2013-05-20}}</ref><ref name="Nasa">{{cite web|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/11649/1/02-0194.pdf|title=In-FEEP Thruster Ion Beam Neutralization with Thermionic and Field Emission Cathodes|quote=liquid state and wicked up the needle shank to the tip where high electric fields deform the liquid and extract ions and accelerate them up to 130 km/s through 10 kV|access-date=2007-11-21|first1=Colleen|last1=Marrese-Reading|first2=Jay|last2=Polk|first3=Juergen|last3=Mueller|first4=Al|last4=Owens|url-status=dead |archive-url=https://web.archive.org/web/20061013162109/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/11649/1/02-0194.pdf|archive-date=2006-10-13}} {{PD-notice}}</ref> The electric field created by the emitter and the accelerator then accelerates the ions. An external source of electrons neutralizes the positively charged ion stream to prevent charging of the spacecraft.