up to Ie=60 kA, the screw pinch will become unstable, because qPinch«1. During the instability the poloidal compression coils will be pulsed and the ST will be generated around the screw pinch. The main g oals of the Proto-Sphera experiment will be to compress the ST to the lowest possible aspect ratio, in a time of about 1500 AlfvØn times, and to show that efficient helicity injection can maintain a stable configuration for at least one resistive time (50 ms). The benchmark Proto-Pinch has been built and operated, with the goal of testing modular units of the cathode and of the anode. Proto-Pinch has produced, within a Pyrex vacuum vessel, Hydrogen and Helium arcs in the form of screw pinch discharges, stabilized by two poloidal field coils located outside the vacuum. Proto-Pinch, with an anode-cathode distance of 0.75 m and a stabilizing magnetic field up to B=1.5 kG, has a current capability of Ie=1 kA, (with a safety factor qe ~ 2 The extrapolation to the 100 cathode modules required for Proto- Sphera, shows that the cathode will be heated by a total AC current Icath=60 kA (rms), with a total heating power Pcath=850 kW. II - Toroidal Plasma Formation and the TS-3 Experiment The formation of the ST is obtained by the kink destabilization of a screw pinc h, through an increase of the longitudinal arc current, as demonstrated on the TS-3 experiment (University of Tokyo). Figure 1 sketches the l inear and nonlinear phase of a kink unstable screw pinch, with longitudinal field BZ and ëtoroidalí field B , that means a pinch winding number qPinch = 2 Pinch BZ/ LPinch B..