The key discovery for the improvement was :
no metal surface penetrated by B fields must occupy more than about 1E-4 to 1E-5 of the total surface available to the recirculating electrons. If this dead fraction is larger, there is NO hope of net power from any such machine. AND, it is essential that the device be recirculating, i.e. that the electrons can circulate out and back through the cusps all over the machine. It is consistent with the need for electrons to recirculate about 100,000 times before being lost to collisions with structure, to yield net power.
Here is a description of his work which had some government funding for a demo but needs $200 million for a full scale system
One of the biggest obstacle is the world-wide tokamak lobby, which perpetuates the fraud that Hirsch, Trivelpiece and Bussard foisted on the country in the 1970's when they started the big tokamak ball rolling.