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Current drive

A method of generating current in a tokamak using radiofrequency waves or neutral beam injection. In order to create a properly shaped helical field, a current must flow through the plasma in the tokamak. This is created by a transformer pulse, but to operate the tokamak continuously and not in pulsed mode, another method current drive is needed. This is achieved by using radio waves of suitable frequency (lower hybrid range) to accelerate the electrons in the plasma, or by tangential injection of neutral particles which then transfer their energy to the charged particles in the plasma. Current drive is also being applied to control instabilities and to optimise confinement.