Microwave measurements of electron density in a spherical inertial-electrostatic confinement system using six ion guns

The electron density in a spherical inertial-electrostatic confinement device using six ion beams has been studied with microwave techniques involving the fundamental and higher order cavity resonances. Thermal expansion problems were circumvented by switched operation of the device. The deuterium background pressure was found to be a dominant factor in determining n/sub e/ throughout the entire range of 0.4 to 10 milliTorr. With 1 m Torr pressure and 10 mA total ion current (at 20 to 40 keV) central electron densities of the order 109 electrons/cm3 were estimated, with total population of approximately 1010 electrons. No evidence of shell structure of the electron density was found, although the use of higher order modes to obtain better spatial resolution was precluded by the low magnitude of n/sub e/. Indirect indication of weak ion trapping was obtained by measurement of the enhancement of neutron flux that resulted when the guns were operated simultaneously