D. Shiffler

A high-power, traveling wave tube amplifier

High-power X-band traveling-wave tube amplifiers (TWTs) have been fabricated and tested. The tubes have gains ranging from 13 to 35 dB at 8.76 GHz and output powers ranging from 3 to 100 MW. The amplifiers are driven by the interaction of a slow space-charge wave, propagating on an electron beam, with an electromagnetic wave supported by the structure. The electron beam, which is produced from a magnetic-field-immersed field-emission cathode, has an energy of 850 keV, a current in the 1-kA range, and a pulse duration of 100 ns. The amplifiers are designed to operate as narrow-band devices in the TM/sub 01/ mode. A report is presented on the amplifier characteristics, and their performance is compared with calculated performance using conventional TWT theory. The scaling of the gain and bandwidth with the beam current are approximately as expected from theory, but the absolute magnitude of the gain is somewhat greater than expected. >

A high-power two stage traveling-wave tube amplifier

Results are presented on the development of a two stage high‐efficiency, high‐power 8.76‐GHz traveling‐wave tube amplifier. The work presented augments previously reported data on a single stage amplifier and presents new data on the operational characteristics of two identical amplifiers operated in series and separated from each other by a sever. Peak powers of 410 MW have been obtained over the complete pulse duration of the device, with a conversion efficiency from the electron beam to microwave energy of 45%. In all operating conditions the severed amplifier showed a ‘‘sideband’’‐like structure in the frequency spectrum of the microwave radiation. A similar structure was apparent at output powers in excess of 70 MW in the single stage device. The frequencies of the ‘‘sidebands’’ are not symmetric with respect to the center frequency. The maximum, single frequency, average output power was 210 MW corresponding to an amplifier efficiency of 24%. Simulation data is also presented that indicates that the...

High‐power traveling‐wave tube amplifier

A high‐power X‐band traveling‐wave tube amplifier has been fabricated and tested. The tube has a 17 dB gain at 8.76 GHz and an output power of order 10 MW. The electron beam has an energy of 850 keV and a beam current of 1 kA. Results are presented showing the characteristics of the amplifier.

Theoretical studies of high‐power Cerenkov amplifiers

The main theoretical aspects of the experiments performed and reported recently are discussed here. First the one stage amplifier is considered. As a preliminary step the behavior of the electrons is followed in the phase space at different points along the interaction region. This analysis reveals that about 30% of the interaction region is utilized for construction of the electron bunches. It is shown that although the average energy of the electrons remains unchanged along most of the amplifier, their energy spread increases substantially. Since the system consists of two long tapered sections, it is suggested that the effective length of the interaction region might be significantly longer than the physical length of the uniform structure. It is further suggested that the electrostatic periodic potential induced by the beam may also improve the interaction process. The next subject addressed here is the bandwidth of a single stage amplifier. It is shown that the reason for the narrow measured bandwidt...

Sideband development in a high-power traveling-wave tube microwave amplifier

The work presented describes the characteristics of single stage and severed high‐efficiency, high‐power traveling‐wave tube amplifiers operating in X band at 8.76 GHz. Average amplified output powers of 210 MW have been achieved at 24% efficiency. At high output power levels (≳100 MW) sidebands develop increasing the average radiated power to over 400 MW with a microwave conversion efficiency of over 45%. In single frequency operation phase stability to within ±8° has been demonstrated.

A High Power Travelling Wave Tube (TWT) Amplifier

Preliminary results are reported on the design and performance of a high power travelling wave tube amplifier. The amplifier is designed to work in the TMoi mode of a cylindrical waveguide and to operate in X band. The signal from a 250 kW magnetron is used as the input source for the amplifier. Details are presented of the amplifier design, the input coupler, and of the performance of the system when an 800 kV, 1.4 kA, POO nsec. duration pencil electron beam is used as the primary power source. Initial results indicate that the amplifier has a gain of 29dB at a frequency of 9.09 GHz, and an output power in excess of 100 MW.

Review of high power traveling wave tube amplifiers

The authors review work performed on high-power traveling wave tube amplifiers. The tubes operated in the X-band at 8.76 GHz with both a single stage and severed amplifier configuration. The single stage amplifiers provide useful gain (i.e. no oscillation) in the current range from 800 to 1700 A. The output is monochromatic until the output power reaches 70 MW, at which point a sideband structure develops in the frequency spectrum. Above 1.7 kA, the tube goes into oscillation from positive feedback. To eliminate the oscillations, the amplifier was severed. The severed amplifier achieved a total overall power output of about 400 MW, as verified by calorimetry. The power at the carrier frequency was 210 MW, giving an amplifier efficiency of 24%. Theoretical work has been performed to investigate the amplifier performance, including the sidebands. Most of the effects seen here can be attributed to finite length effects.<<ETX>>

Pulse power driven high power traveling wave tube amplifiers

Results on the development of a two-stage, high-efficiency, high-power 8.76-GHz severed traveling wave tube amplifier are presented. Peak powers of more than 400 MW have been obtained over the complete electron beam duration, with a conversion efficiency from the electron beam to microwave energy of 45%. The maximum, single-frequency, average output power was 210 MW, corresponding to an amplifier efficiency of 24%. The severed amplifier showed an asymmetric sideband-like structure in the frequency spectrum of the microwave radiation. Theoretical analysis and simulation are used to examine the device performance. A substantial number of electrons are found to be accelerated in the slow wave structure.<<ETX>>

High-gain high-efficiency TWT (traveling wave tube) amplifiers

Results are presented from recent research carried out on the development of high efficiency, high power traveling wave tube amplifiers. A rippled wall traveling wave tube is used as a slow wave structure for wave interactions with an 850 kV, 1 kA electron beam. A 100 kW signal from a magnetron is injected at the front end of the device and amplified by 15-30 dB giving an output power of 100 MW from a single stage amplifier. At higher gains the system tends to oscillate due to feedback from impedance mismatches at the structure ends. To overcome this we have used a severed amplifier consisting of two identical amplifiers in series and separated by an absorbing graphite section between the two amplifiers. With this device we have obtained 400 MW output power with an energy conversion efficiency of 48%. We shall present a comparison between the amplifier characteristics for the single and two stage amplifiers. Peak output powers are obtained in the severed amplifier at a beam current of 900 A; however, sidebands have developed and the output is no longer single frequency. It should be noted that the relative distribution of power in the sidebands compared to the center frequency varies with the beam current and that the sideband power can approach 50% of the total radiated intensity at high beam currents. The sidebands are asymmetrically located on either side of the carrier frequency with the upper sideband displaced from the carrier by about three times the frequency shift for the lower sideband. The authors discuss mechanisms leading to the sideband behavior described. It seems likely that most of the phenomena observed can be accounted for by finite structure length effects, which lead to resonances in the transmission coefficient for the structure. Other effects of importance include a substantial spread in the electron energy spectrum as the wave develops.

Development of sidebands in ultra high power traveling wave tube amplifiers

Results are presented from recent research on the development of high-efficiency, high-power traveling-wave-tube amplifiers (TWTAs). A rippled wall TWTA is used as the slow-wave structure for wave interactions with an 850 keV, 1 kA, 100 ns duration electron beam. The output power of the tube is in excess of 400 MW at 8.76 GHz, corresponding to an electron beam to microwave energy conversion efficiency of 48%. At high output power levels (>100 MW), sidebands are observed to develop which carry an increasing fraction of the output signal as the beam current is increased. The sidebands are asymmetrically located with respect to the center frequency of the amplifier and do not appear to be associated with trapped particles. It is postulated that the sidebands result from finite length effects in the short amplifier sections used.<<ETX>>