Gyrotron-traveling wave-tube circuits based on lossy ceramics

A gyrotron-traveling-wave tube amplifier experiment with a ceramic loaded interaction region

“…4 shows the measured cold test results for three circuit ceramics compared with calculations performed using a version of CASCADE [23] which was modified to include lossy, dielectric material. The cold loss for the TEoi mode was measured to be 3.51 dB/cm at 35 GHz, which agreed well with both the CASCADE value of 3.39 dB/cm and the theoretically calculated value of 3.44 dB/cm at 35 GHz [7]. Similar'agreement was obtained for a measurement of the TEn mode.…”

“…The radial thickness of the ceramic was 0.14 cm and was chosen to be where the TE02 mode attenuation reaches a minimum that occurs when the field at the dielectric is small. This resulted in the field structure in the vacuum being close tothat of the unloaded TE 0 i mode with a similar propagation constant [7]. The total loaded interaction region of 23-cm length and 0.5495-cm radius consisted of 20 ceramic rings alternating with copper rings of 0.15-cm length.…”

“…The required loss rate for stability of the TE 0 i operating mode was calculated to be 3.44 dB/cm at 35 GHz [7]. The corresponding loss rates for the BWO modes, TEn, TE 2 i, TE 0 2 were 3.04 dB/cm at 25 GHz, 12.5 dB/cm at 28 GHz, and 18.4 dB/cm at 61 GHz, respectively.…”

“…The copper rings were incorporated into the design for ease of assembly and to help collect stray electrons that could potentially cause breakdown. Also, including metal rings allows the loading of nonaxisymmetric parasitic modes to be adjusted selectively due to the absence of axial currents in the TE 0n modes [7]. I The cold test, transmission properties of three circuit ceramics plus copper rings (total length 3.45 cm) were measured for the TEoi operating mode.…”

“…In this paper, we present a new method of stabilizing the gyro-TWT that involves controlled loading of both the TE 0 i operating mode and the backward wave oscillations. A high thermal conductivity, lossy ceramic material was used to suppress oscillations with the added advantage of being high-average power compatible [7].…”