Current Drive By Dc Helicity Injection In FACT Spheromak

Various alternative methods for current drive have been proposed in magnetically confined plasmas. The method of "dc" or" electrostatic" helicity injection using electrodes is expected to be more efficient and inexpensive than the low-hybrid wave and the neutral beam injection. The concept of helicity injection in spheromak is based on "Taylor principle" which is shown to be operative by a large amount of observations. The relaxation causing the magnetic turbulence is thought to be essentially necessary for spheromak current drive. In the FACT device, the magnetic helicity is injected additionally into the seed spheromak produced in the flux conserver (FC) by the normal magnetized coaxial gun. Consequently, the spheromak has been sustained successfully for much longer than the resistive decay time of the magnetic field. Toroidal current I
_t
of the sustained spheromak reaches about 20 kA and its discharge duration time of over 800 μs is five times as large as a lifetime of the seed spheromak.