A couple of scientists from the European Space Agency claim to have observed an artificially-generated gravitational field while rotating a superconductive disk:
http://www.esa.int/S...0L6OVGJE_0.html
http://www.scienceda...60325232140.htm
Here is the link to their publication:
http://arxiv.org/abs/gr-qc/0603033
They're claiming 10^-4g (ie. ~ a ten-thousandth of a g) at approx 6500 rpm
If this phenomenon is real, it could mean the advent of anti-gravity, or even field-based propulsion where no propellant is required.
According to Dr Tajmar, the size of the disk is irrelevant to the effect. By this, I assume he means volume/dimensions/diameter of the disk doesn't affect things, but I'd assume that mass does.
If this gravitomagnetic field scales up with rpm, then I'll assume that the smaller the disk the better, since smaller objects are capable of rotating faster. Nano-scale superconductive gyroscopes might then be able to rotate far faster than macro-sized ones, thus possibly generating more powerful fields.
If you compare the shape of a tube to that of a disk, a tube has a much smaller diameter which thus facilitates a much higher rate of rotation. If the tube is aligned vertically along the axis of gravity, it could be equivalent to a bunch of stacked rings or disks, perhaps linearly scaling up that gravitational field with tube length. I wonder what a superconductive helical shape would do, if it were rotated about the helical axis?