Dean E. Pershing

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

The design and experimental study of a 35-GHz gyrotron-traveling-wave tube (gyro-TWT) amplifier operating in the circular TE/sub 01/ mode at the fundamental cyclotron harmonic are presented. The interaction circuit in this experiment consisted of a new type of ceramic loading that provided the required loss for stable operation. A saturated peak power of 137 kW was measured at 34.1 GHz, corresponding to a saturated gain of 47.0 dB and an efficiency of 17%, with a -3-dB bandwidth of 1.11 GHz (3.3%). Peak output powers in the range of 102.1 to 148.6 kW with -3-dB bandwidths of 1.26 and 0.94 GHz, respectively, were measured by varying the operating parameters. The gyro-TWT was found to be zero-drive stable at these operating points, demonstrating that ceramic loading is a highly effective means of suppressing spurious oscillations in gyro-TWTs. This type of ceramic loading has the added advantage of being compatible with high average power operation.

A TE/sub 11/ K/sub a/-band gyro-TWT amplifier with high-average power compatible distributed loss

Current amplifier research at the Naval Research Laboratory Vacuum Electronics Branch emphasizes techniques to extend the bandwidth and average power capability of gyro devices for millimeter wave radar applications. This paper will discuss the implementation of a wideband high-gain gyro-traveling wave tube amplifier design, with a measured peak output power of 78 kW, gain /spl sim/60 dB, and a 3-dB bandwidth of 4.2 GHz (12%) at 52 kW in K/sub a/-band. The 3-dB saturated bandwidth at 70 kW is 6 GHz (17%), which is also the instantaneous bandwidth with appropriately tailored input power (e.g., gain equalizer). The amplifier operates in the TE/sub 11/ mode and for stabilization employs a high-average power compatible diffractive loading technique.

Experimental investigation of W-band (93 GHz) gyroklystron amplifiers

The results from W-band gyroklystron amplifier experiments are presented. Two circuit configurations, WGKL1 and WGKL2, have been demonstrated. The WGKL1 circuit achieved 67 kW peak output power, corresponding to 28% efficiency, for a 55-kV, 4.3-A electron beam. The full width half maximum (FWHM) bandwidth was measured to be 460 MHz, a significant increase over the bandwidth demonstrated in previous W-band gyroklystron experiments. The amplifier was unconditionally stable at the operating point. The WGKL2 circuit, which was designed to have a broader bandwidth, produced 60 kW peak output power at 25% efficiency with a 640 MHz FWHM bandwidth for a 58 kV, 4.2 A electron beam. The results from both experiments are compared with theory and good agreement is obtained.

Development and testing of a high-average power, 94-GHz gyroklystron

The development of a 10-kW average power, 94-GHz gyroklystron amplifier is described. This average power was obtained with 11% radio frequency (RF) duty factor and 92-kW peak power in the TE/sub 01/ circular cavity mode. The instantaneous bandwidth was 420 MHz, and the efficiency was 33.5%. Low-duty-factor testing also yielded a peak power of as much as 115 kW with 600-MHz instantaneous bandwidth. This development effort was carried out over the past three years and represents record average power performance in an amplifier at this frequency.

Demonstration of a 10 kW average power 94 GHz gyroklystron amplifier

The experimental demonstration of a high average power W-band (75–110 GHz) gyroklystron amplifier is reported. The gyroklystron has produced 118 AW peak output power and 29.5% electronic efficiency in the TE011 mode using a 66.7 kV, 6 A electron beam at 0.2% rf duty factor. At this operating point, the instantaneous full width at half-maximum (FWHM) bandwidth is 600 MHz. At 11% rf duty factor, the gyroklystron has produced up to 10.1 kW average power at 33% electronic efficiency with a 66 kV, 4.15 A electron beam. This represents world record performance for an amplifier at this frequency. At the 10.1 kW average power operating point, the FWHM bandwidth is 420 MHz. At higher magnetic fields and lower beam voltages, larger bandwidths can be achieved at the expense of peak and average output power.

High-power four-cavity S-band multiple-beam klystron design

We develop a methodology for the design of multiple-cavity klystron interaction circuits. We demonstrate our approach with the detailed design of a collector and a four-cavity circuit for a multiple-beam klystron (MBK) operating in the fundamental mode at a center frequency of 3.27 GHz (S-band). These elements are designed to be used with a 32-A 45-kV magnetically shielded eight-beam electron gun currently under fabrication . Upon integration of the gun, circuit, and collector, the MBK will be used for beam transport and beam-wave interaction studies and to validate developmental design codes and design methodologies. The device has a predicted gain of 33 dB at a peak pulsed output power of 750 kW with a corresponding electronic efficiency of 52%. For the present design, broad bandwidth is not a design objective, and the 3-dB bandwidth is 2.5%. Downstream of the output cavity, the magnetic field profile and the interior surface profile of the collector are carefully shaped to minimize the space-charge potential depression at the entrance to the collector, minimizing reflected electrons. The maximum calculated instantaneous power density on the walls of the collector is approximately 55 kW/cm/sup 2/; at low duty cycles (<1.8%), the average power density is well within the limits for liquid cooling for pulse lengths up to 1.3 ms.

Demonstration of an S-band, 600-kW fundamental-mode multiple-beam klystron

We present initial experimental results from the successful operation of a 600-kW peak, fundamental-mode multiple-beam klystron (MBK). The eight-beam device operates at a cathode voltage of /spl sim/45 kV and a total beam current of /spl sim/32 A with an axial guiding magnetic field of 1.8-2.2 kG. In the absence of radio-frequency (RF) drive, the measured beam transmission is in excess of 99%; at a driven frequency of 3.25 GHz, the measured beam transmission at saturation is /spl ges/97%, where the four-cavity circuit generates a peak power of /spl sim/600 kW with an electronic efficiency of 40%. The measured beam transport and RF performance are in excellent agreement with predictions made by the three-dimensional gun/collector code, MICHELLE, and the large-signal klystron code, TESLA. The accuracy of the design codes enabled the achievement of a working device in a single hardware design pass.

Amplifier performance of the NRL ubitron

Abstract Operation of the Naval Research Laboratory K u -band ubitron has successfully demonstrated a high power/efficiency and broad bandwidth. This device employs a helical wiggler/axial guide field configuration. Performance levels achieved at 16.6 GHz can be summarized as a peak power of 4.2 MW for an efficiency of 17.5% and a gain of 29 dB, and an instantaneous bandwidth of 22%. Substantial beam loss was observed. The specific loss rate was correlated with output power, and reached a level of 50% beam loss at the 4.2 MW level. Nonlinear simulations of the experiment are in good agreement with these observations.

Development and demonstration of high-average power W-band gyro-amplifiers for radar applications

The results of a focused program to develop high-power W-band gyro-amplifiers, which culminated in the demonstration of record average output powers from amplifiers in this band, are described. Following an experimental and theoretical study of low-duty prototype amplifiers, two high-average power devices were designed, built, and demonstrated. The first high-average power amplifier achieved 10.1-kW average output power at 33% efficiency in the TE/sub 0.1/ mode at 93.8 GHz. The instantaneous bandwidth was 420 MHz and the saturated gain at the 10.1-kW point was 32 dB. The second high-average power gyroklystron, designed for improved bandwidth, demonstrated 10.2-kW average power at 31% efficiency with 700-MHz instantaneous bandwidth and 33-dB saturated gain. The measured results of the low-duty prototype amplifiers and the high-average power gyroklystrons are described in detail. In addition, theoretically predicted results for a high-average-power W-band gyrotwystron amplifier, which is currently in construction, are presented.

Nonlinear theory of the free‐electron laser based upon a coaxial hybrid wiggler

A three‐dimensional nonlinear formulation of a free‐electron laser based upon a coaxial hybrid iron (CHI) wiggler is described. The CHI wiggler is created by insertion of a central rod and an outer ring [composed of alternating ferrite and dielectric spacers in which the ferrite (dielectric) spacer on the central rod is opposite to the dielectric (ferrite) spacer on the outer ring] along the axis of a solenoidal. An analytic model of the CHI wiggler is developed which is in good agreement with the Poisson/Superfish group of codes. The free‐electron laser (FEL) formulation is a slow‐time‐scale analysis of the interaction of an annular electron beam with the CHI wiggler in a coaxial waveguide. The electromagnetic field is represented as the superposition of the vacuum transverse electric (TE), transverse magnetic (TM), and transverse electromagnetic (TEM) modes of the waveguide, and a set of nonlinear second‐order differential equations is derived for the amplitudes and phases of these modes. These equation...