Two-stage heating mechanism for plasma fusion at 10 MK

A two-stage heating mechanism for plasma fusion at 10 MK with extremely heated ³He ions is developed. To realize thermonuclear fusion in laboratory, plasmas must be heated to 100 MK and above. The ohmic heating process is the simplest, in which an electric current that is driven through a plasma can heat the plasma up to 10 MK. Beyond this limit the resistivity in the plasma is too low for the current to be significantly dissipated. Our previous studies on the theory of solar ³He-rich events have shown that current-driven electrostatic H-cyclotron waves can be very efficient at heating ³He through the second harmonic resonance. The ³He temperature can be increased by a factor of 10-100 within only hundreds of the H gyro-period. This preferential heating of ³He can be applied as the second stage heating of an ohmically preheated laboratory plasma for fusion with ³He. As an electric current is driven through, the plasma is gradually heated up to 10 MK due to the ohmic dissipation and saturates at this level of temperature. When the current continuously increases up to a critical point, the electrostatic H-cyclotron waves are excited, which can further heat ³He to 100 MK and above, at which the nuclear fusion between the extremely hot ³He and the other relative cold D ions can occur. In a tokamak (e.g., ITER), if the plasma is composed of e, H, D, and ³He with abundances n_H > n_D >> n_3He, then, when ³He is preferentially heated to 100 MK and above by the current-driven electrostatic H-cyclotron waves, the plasma dominant species of ions (H and D) are still around 10 MK. This new mechanism for plasma fusion can also greatly reduce the difficulty in controlling the plasma as well as avoiding any explosion of the machine when the extremely hot ³He ions fuse with the relative cold D ions.