Solo wrote:Joseph, the point of the quadrupole field is to stabilize m=2 MHD instabilities that plague the FRC. If you recall the basic Polywell theory, the whole point of using a cusp field is that since it *IS* a multipole field, it is inherent stability to all MHD activity.
It is terminology issue and usually by conventional terminology quadrupole magnets are axially symmetric magnets providing to charged particles beams the so called "strong focusing" capability.
For example betatrons and synchrotrons provide so called "weak focusing fields" and can produce mili-amperes orders currents due to space charge limitations. But adding strong focusing assets e.g. quadrupoles we will get so called "modified betatrons" (FFAG betatron in quadrupole case) expanding space charge limitation and might producing thousands amperes order currents.
And magnets (magnetic mirrors) in Polywell have not axial symmetricity. As Polywell is a spheric device cinfining the certain space from any direction.
Yes, being flexible in terminology certainly we can call tetragonal shaped Polywell's mag system "quadrupole", more known cube shaped - "sextupole", etc.
But confinement concept in mirror machines and strong focusing in particles accelerators are very different things by their sense.