Microwave-cavity modes directly observed in a Penning trap

Abstract
The microwave-cavity mode pattern has been directly observed in an old-style compensated Penning trap by a simple bolometric technique which monitors changes in the temperature of the axial center-of-mass motion for a cloud of electrons. The method allows one to easily determine the position of individual modes to a precision better than 0.01%. Presently, over 60 modes have been observed for fields between 17 and 60 kG and an upper limit estimate of 2300 has been made for the cavity Q.