Faraday Cup Design for the ILIS1 Ignition Test

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For the upcoming ignition test of the AIS-ILIS1 ionic liquid ion source electrospray thruster, I need a way to definitively verify ignition, as well as start to gauge performance to estimate thrust and ISP. One of the simplest and most powerful ways to do so is the use of a Faraday cup, which is quite literally just a metal cup placed in the way of a charged particle beam to collect charge, therefore giving the ability to read beam current. Below is a CAD render of the simple Faraday cup design that’s in the works for the ILIS1 ignition testing. It’s super bare bones and as minimal as you can get – literally just a 2″ copper pipe cap bolted to a scrap PEEK base with bolt connection at the back for current readout!

ILIS1 Faraday Cup

While I would love to design an optimized Faraday cup with all the bells and whistles – shielding, deep tapered conical bore for secondary electron capture, and a secondary electron suppression electrode, I just don’t have the luxury or funds right now. Sometimes simple is best! The cup will slide right into the chamber in front of the thruster during operation to collect beam current. By knowing current, as well as voltage from the thruster readout, and the charge to mass ratio of the fuel (which is simple to calculate based on ion mass parameters of the fuel), not only can I definitively confirm ignition, but can start to quantity expected thrust and ISP.

The parts for the build have been ordered and are on the way. I expect this build to be completed in the next few days, with thruster mounting to follow shortly. After that, it is assembling and testing the fueling station, then the big test itself!