Can a single proton be trapped in a Penning trap? And what happens to it?

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Can a single proton be held in a Penning trap and for how long? Has it been done? Who did it?

 

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http://www.aip.org/png/html/penning.htm

This is a graphic of a Penning trap. I am hoping to come across an expert on Penning traps who can discuss the thresholds, i.e can one proton be trapped. Is there any way to observe the trapped ions? Is there any experiments done with protons and what happens to them while in a trap, i.e. do they leak out, do they form hydrogen while in there, etc.?