Nonlinear control of transport in drift wave turbulence

The control of the dynamics of drift waves is investigated experimentally in a linear laboratory plasma device. The control parameter is a mode selective drive of currents parallel to the magnetic field using an arrangement of eight azimuthally arranged electrodes and eight saddle coils, respectively. The driven currents resemble the intrinsic drift mode currents. Single coherent drift modes are synchronized in frequency by both control setups only if the control signal has the same mode structure and direction of phase velocity as the drift mode. The frequency range of synchronization depends nonlinearly on the amplitude of the driven current. In drift wave turbulence the turbulent fluctuations are synchronized to a single coherent drift mode to the expense of the energy of the broadband turbulent fluctuations. As a result the phase shift of density and potential fluctuations decreases considerably, thereby reducing the cross-field transport.