Experiments on fusion reactions produced by adiabatic compression of plasma vortex structures are discussed. The TRISOPS machine at the University of Miami has been modified by improving the preionization of the plasma and increasing the ring frequency of the conical theta-pinch coils. The results obtained with a series of experiments leading up to the latest machine, TRISOPS VIII, are reviewed. It has been possible, with this modified machine, to obtain ion temperatures of 1 keV before secondary magnetic compression without any magnetic guide field. Ion temperatures of over 6 keV are obtained with secondary magnetic compression fields of 30000 G. The plasma pressure, in both instances, must be balanced by hydrodynamic forces. Ion temperatures and densities were measured by three different methods. All methods yield essentially the same results. The plasma was held in stable equilibrium for 30 µs and neutrons were produced for 40 µs.