In order to confirm the possibility of using the ferritic material in magnetic fusion devices, a tokamak discharge with a ferritic (F82H: 8%Cr-2%W-0.2%V-0.04%Ta-Fe) first wall was tried successfully in the Hitachi Tokamak HT-2. This is a small tokamak with a major radius of 41cm, a minor radius of 11cm, a toroidal field of B_t<2.5T, plasma current of I_p<55kA and a SS304 vacuum vessel. The ferritic steel is considered as a candidate material for fusion reactor structure, however it generates undesired error magnetic field and outgas. These are why we tested that ferritic first wall. Fourty-eight ferritic plates (7.5mm thick) were installed surrounding the plasma. The HT-2 has 64 magnetic sensors, 12 of which were installed at plasma side of the plates for the present work . However, the same poloidal magnetic field control technique as before their itstallation was used.

After the installations, a vacuum pumping test was done with an 160 $B!n (J 6-hour baking. It took one week to reach below 10^-7 Torr, and after another week, 2.5x10^-8 Torr was reached, which was roughly comparable with that before installations. The ferritic plates did not degrade the vacuum quality. Discharge trials were done. However outgasses of H2O, CO, CO2 were produced, which disturbed the discharge. About 1500 discharges were made before normal stable discharges (20kA IP, 40ms duration) could be obtained.

In order to understand the poloidal magnetic field configuration, a computer code to reconstruct the magnetic field taking into account the ferritic plates was developed. The ferritic plates were modeled by introducing surface magnetizing currents. Their magnitudes as well as magnitudes of coil currents, eddy currents and plasma current, were fitted to the measured magnetic data. The ferritic plates generated equilibrium vertical field (roughly 10^-3T) and it should be taken into account for the reconstruction.

The ferritic (F82H) vacuum vessel was concluded to be a possible structuaral material for tokamaks. However, it is necessary to investigate plasma confinement with the local magnetic field due to ferritic materials, in large tokamaks.