Terrella for Advanced Undergraduate Physics Laboratory

A terrella has been in use in the Advanced Laboratory for undergraduates in the Physics Department at the University of Wisconsin-Madison since spring 2016. Our terrella is a permanent magnet on a pedestal which may be biased in various ways. In the vacuum region B $\leq $ 200 gauss; for typical operation $p$ ~ $10^{-4}$ Torr. Plasma may be created by thermionic emission from a filament or by an S-band magnetron. Students are guided through diagnosis of the terrella plasma using spectroscopy and swept Langmuir probes. A suite of supporting experiments has been developed to introduce basic plasma phenomena, such as the Child-Langmuir law.