The simplest and most obvious method with which to provide confinement of a plasma is by a direct-contact with material walls, but is impossible for two fundamental reasons: the wall would cool the plasma and most wall materials would melt. We recall that the fusion plasma here requires a temperature of ~108 К while metals generally melt at a temperature below 5000 K.

Further, even for a plasma not in direct contact, there exist problems with a material wall. High temperature particles escaping from the plasma may strike the wall causing so-called "sputtered" wall atoms to enter the plasma. These particles will quickly become ionized by collisions with the background plasma and can appear as multiply-charged ions which are known as fusion plasma impurities. Then, as shown in the analysis leading to Eq. (3.44), the bremsstrahlung power losses increase with Z2 thus further cooling the plasma.