The main difference is the plasma circulates. With the donut, the problem is similar to trying to inflate a balloon that has a weak point in it. Blowing cause

The main difference is the plasma circulates. With the donut, the problem is similar to trying to inflate a balloon that has a weak point in it. Blowing causes the weak point to inflate instead of the balloon. Plasmas are electrically charged and have their own magnetic field. Trying to squeeze down on the plasma inside the donut shape to cause fusion causes the plasma's own magnetic strength to increase and counter the field being applied to it. The stellarator works with the plasma's magnetic field instead of against it by spiraling it around in circles.