Mac Cameron and Lily Hanson
University of Minnesota
Methods of Experimental Physics Spring 2012
We measured the change in frequency of a microwave signal resonating in a copper pipe (waveguide) when the index of refraction inside the pipe is altered by the presence of unmagnetized or magnetized collisionless plasma. We reproduced an experiment described by Julie Orr and Richard Wolfson, in which a collisionless plasma is provided by the decaying plasma of a fluorescent lamp just after it is turned off. The change in resonant frequency when the magnetic field strength is turned on can be used to calculate the electron density in the waveguide at a given time in the plasma?s decay. We expected the electron densities to be on the order of 10^15 to 10^17 m-3 and decaying with a time constant of at least 0.5 ms. Our results showed the electron density decreasing exponentially from an initial extrapolated value of 7±1x1016 ??-3 with a time constant of 3.2±0.8 ????.