WALL AND TEMPERATURE EFFECTS ON ELECTROSTATIC OSCILLATIONS OF SPHEROIDAL NONNEUTRAL ELECTRON PLASMAS IN THE MULTIRING ELECTRODE TRAP

Electrostatic oscillations of spheroidal non-neutral electron plasmas are experimentally investigated with the multiring electrode trap whic h provides an electrostatic quadrupole potential with a long axial ext ent and enables confinement of plasmas with large aspect ratios. The f requencies of axial modes l = 2 and 3 of trapped plasmoids shifts upwa rds from those predicted by Dubin's cold plasma theory for the free bo undary case, mainly due to the image charges induced on the conducting electrodes. These frequencies continue to increase as the plasma temp erature is increased from 0.03eV to 1.5eV by rf heating. This temperat ure dependence can be interpreted as a change in the dielectric tensor caused by the temperature increase.