These represent the most important controls in a magnetic fusion reactor.
Plasma Density
Measures how close together particles are. If the plasma particles are closer (higher density values), they are more likely to collide and fuse.
Auxiliary Heating Power
Power must be put into the plasma to make the charged particles (ions) move faster (a scientist would say the power raised the temperature of the plasma). If two ions collide at a high enough speed, they can overcome their natural repulsion and fuse.
Magnetic Field
If the plasma particles strike the surrounding walls, they slow down again. So, a tokamak uses magnetic fields to keep the plasma away from the walls (we say that the magnetic field confines the plasma).