Polywell and Hall Effect Thruster Similarities

[Aero]

It strikes me that a Hall Effect Thruster, (HET), is much like a half of a Bussard Fusion Reactor, (BFR). That is, instead of an enclosed core, the HET is open on one side and the ions are expelled to create thrust. Knowing that there are some very knowledgable people on this forum, I wonder how far the comparison could be carried, and if we can see any obvious technical improvements.
For HET, see the "Operation" paragraph, here.
http://en.wikipedia.org/wiki/Hall_effect_thruster
and look at a research paper, here.
http://www.me.mtu.edu/researchAreas/isp/projects.html

Hall thrusters employ a magnetic field applied transverse to an accelerating electric field to emulate virtual accelerating electrodes. Historically, the cross-field electron mobility in HEA's has been shown to be 1,000 times greater than predicted by classical plasma theory, yet an explanation for this discrepancy is absent.

Being a Polywell fan, I found that paragraph very interesting. I wonder if polywell has the same unexplained factor of 1000 showing up in its transport? Or, if perhaps it is 1,000 times lessor, due to the enclosed nature of the Polywell core?

[Aero]

No comments? Well, I was wondering what would happen if one were to design a HET using 1.5 MV, instead of the 300 V they commonly use.

I was also wondering why the fuel needs to be heavy atoms. I can understand why the fuel needs to ionize easily, but why does it require heavy atoms? I mean, using something like a BFR as a power source, basically unlimited power, comparatively, then so what if it is not quite as efficient as the current 63% energy efficient thrusters? I guess the question is, can a Hall Effect Thruster be scaled up to multi megawatt power levels? I know that a VASIMR can be, how about a Hall Effect Thruster?