Microwave interferometer and refractometer for the WB-8 polywell fusion device

The WB-8 chamber is an inertial electrostatic confinement device which is being tested by Energy Matter Conversion Corporation in an attempt to study the viability of their Polywell design as a source of fusion energy. One of the primary diagnostic tools will be a 94 GHz interferometer which will give a line average density measurement of a chord through the plasma. The rate at which ions take part in a fusion event depends heavily on the density, making the interferometer measurements vital in assessing the progress made with WB-8.;In order to take density measurements, a beam must pass through the plasma and be collected on the other end. One of the challenges in building an interferometer is designing lenses that can transmit a suitable beam into the test chamber. The beam leaving a horn antenna is approximately Gaussian. Using Gaussian optics a lens can be used to focus the beam in order to probe the center of the plasma and provide sufficient energy at the receiver.;While the interferometer provides an average density, a more thorough picture of the density profile is needed to have a good understanding of how well the Polywell is functioning. A refractometer is also being built which will transmit a beam similar to that sent by the interferometer. This second beam, with a frequency of 136 GHz, is aimed parallel to the interferometer. Instead of propagating through the center of the plasma, the refractometer beam will have a translating launch point which can probe the plasma through different chords. By detecting the shape and location of the beam at the receiving end of the chamber the hope is that we will have additional information about the density profile.