Mode and Transport Studies of Laser-Cooled Ion Plasmas in a Penning Trap

Abstract. We describe a technique and present results for imaging the modes of a laser-cooled plasma of 9Be+ ions in a Penning trap. The modes are excited by sinusoidally time-varying potentials applied to the trap electrodes, or by static eld errors. They are imaged by changes in the ion resonance fluorescence produced by Doppler shifts from the coherent ion velocities of the mode. For the geometry and conditions of this experiment, the mode frequencies and eigenfunctions have been calculated analytically. A compar-ison between theory and experiment for some of the azimuthally symmetric modes shows good agreement. Enhanced radial transport is observed where modes are resonant with static external perturbations, such as those caused by misaligning the trap with respect to the magnetic eld. Similarly, the plasma angular mo-mentum can be changed through the deliberate excitation of azimuthally asymmetric modes. The resultant torque can be much greater than that from the \rotating wall " perturbation, which is not mode-resonant