Microwave measurements from a gyrotron operating with a neutralizing background plasma

Summary form only given. A high-power gyrotron oscillator experiment that utilizes a neutralizing background plasma has been conducted. A background plasma was injected into a gyrotron interaction region from an upstream array of plasma guns. The peak plasma density available from the plasma guns exceeded n_p>10¹³ cm^-3. The plasma density was measured by 70-GHz microwave interferometry and Langmuir probes. A high-current annular electron beam from a field emission electron gun entered the plasma-filled gyrotron cavity from the upstream side. In the presence of the background plasma, electron beam currents in excess of 10 kA transiting the gyrotron cavity region have been measured. The gyrotron cavity is designed for the excitation of the TE62 electromagnetic mode at f=35 GHz. Computer simulations indicate that powers in excess of 1 GW may be possible. The density of the neutralizing plasma is varied by changing the delay between the firing of the plasma guns and the VEBA accelerator