High-power heating experiment of spherical tokamaks by means of plasma merging

High-power heating of spherical tokamaks (STs) has been investigated experimentally by means of the plasma merging effect. When two STs were coaxially collided, the thermal energy of the colliding ST was injected into the target ST during a short reconnection time (Alfven time). Though the thermal energy increment increased with decreasing plasma q value, thermal energy loss during the following relaxation tended to be smaller with increasing q. The produced high-β STs had hollower current profiles and weaker paramagnetic toroidal field than those of single STs. These heating properties indicate that plasma merging is a promising initial heating method of ST plasmas.