| A quadrupole Penning trap designed to accumulate positron plasmas has been used to study the global plasma modes of electron plasmas, positron plasmas, and ion plasmas. The continuously generated ion plasmas reach the Brillouin density limit and are thus effectively unmagnetized, whereas the electron and positron plasmas are highly magnetized and well confined. The spheroidal equilibrium expected in a quadrupole trap applies to both cases, permitting the use of a new cold fluid theory of the normal modes of the plasmas. The two classes of modes studied experimentally, axial modes of electron plasmas and azimuthal modes of ion plasmas, have frequencies in good agreement with the theory. Anomalous damping of the axial center-of-mass oscillation is observed in a cylindrical trap, but not in the quadrupole trap. For the axial quadrupole mode of electron plasmas, the plasma temperature causes an increase in the frequency which is accurately reproduced by numerical plasma simulations, and which appears to be adequately described by recent work on a warm fluid theory. The use of the electron plasma modes to monitor the size, shape, and temperature of the plasmas is described. This technique is expected to be an important nondestructive tool for the study of positron plasmas. |
