Radial compression and torque-balanced steady states of single-component plasmas in Penning-Malmberg traps

Penning-Malmberg traps provide an excellent method to confine single-component plasmas. Specially tailored, high-density plasmas can be created in these devices by the application of azimuthally phased rf fields (i.e., the so-called "rotating wall" technique). Recently, we reported a regime of compression of electron (or positron) plasmas in which the plasma density increases until the ExB rotation frequency, omega(E) (with omega(E)proportional to plasma density), approaches the applied frequency, omega(RW). Good compression is achieved over a broad range of rotating wall frequencies, without the need to tune to a mode in the plasma. The resulting steady-state density is only weakly dependent on the amplitude of the rotating-wall drive. Detailed studies of these states are described, including the evolution of the plasma temperature, peak density, and density profiles during compression; and the response of the plasma, once compressed, to changes in frequency and rotating-wall amplitude. Experiments are conducted in a 4.8 T magnetic field with similar to 10(9) electrons. The plasmas have initial and final temperatures of similar to 0.1 eV. They can be compressed to steady-state densities > 10(10) cm(-3) and plasma radii < 200 mu m. The outward, asymmetry-driven plasma transport rate, Gamma(o), of the compressed plasmas is independent of density, n, in contrast to the behavior at lower densities where Gamma(o)proportional to n(2). The implications of these results for the creation and confinement of high-density electron and positron plasmas and the creation of finely focused beams are discussed. (c) 2006 American Institute of Physics.