If the plasma touches any material, it will pollute the plasma, and shutdown the process(often disastrously). There are no materials that can contain the plasma. That is why a magnetic field is used to contain the plasma. We started doing this in the 1950's but there was a problem, the magnetic field would be in the shape of a tube, and what do you do with the ends? The Soviets solved this by connecting the two ends to make a donut shape that they called a tokamak. They invented it, so they got to name it, and we all call it a tokamak now.This makes the first containment wall feasible with today's materials.