The millimeter-wave spectrum, generally considered to range from 30 to 300 GHz, is one of the most actively used spectrums today, with applications such as high-data-rate terrestrial and space communications, radar, and electronic warfare. The helix traveling-wave tube (TWT) amplifier has long been a critical component for enabling modern millimeter-wave systems. This paper presents an overview of several recently developed high-power millimeter-wave helix TWTs which have extended the helix TWT performance envelope. In particular, the power-frequency-bandwidth product for these devices has increased by a factor of 4 to over 100 depending upon the application. These helix TWTs operate at power levels up to 1-kW peak power or 500-W average or continuous-wave power and over frequencies from 18 to 46 GHz, with efficiencies up to 60%. The helix TWT performance improvements discussed here have not only kept pace with improvements in rival technologies such as GaN solid-state power amplifiers but also pushed helix TWTs into competition with traditionally higher power and higher frequency vacuum electron devices such as extended-interaction klystrons and coupled-cavity TWTs. Indeed, the modern high-power millimeter-wave helix TWT offers system engineers a singularly attractive amplifier technology with an outstanding combination of small size, light weight, high efficiency, good linearity, high reliability, and large bandwidth.

Latest Advancements in High-Power Millimeter-Wave Helix TWTs

This is Part I of a two-part report on design and manufacturing methods used at SLAC to produce accelerator klystrons. Chapter 1 begins with the history and applications for klystrons, in both of which Stanford University was extensively involved. The remaining chapters review the theory of klystron operation, derive the principal formulae used in their design, and discuss the assumptions that they involve. These formulae are subsequently used in small-signal calculations of the frequency response of a particular klystron, whose performance is also simulated by two different computer codes. The results of calculations and simulations are compared to the actual performance of the klystron.

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High Power Klystrons: Theory and Practice at the Stanford Linear Accelerator CenterPart I

Several types of C-band broadband multibeam klystrons (MBKs) are under development at the Institute of Electronics, Chinese Academy of Sciences. These MBKs operate at various C-band frequencies and have peak powers of 30-200 kW, average powers of 2-10 kW, and bandwidths of 4%-7%. The design considerations for obtaining high power and wide instantaneous bandwidths and test results for these MBKs are presented in this paper. The main technical problems, including a power sag in the band, high voltage breakdown, and non-operating mode oscillation, are also discussed. Further research work for improving the performance of these MBKs is described

Research Progress on C -band Broadband Multibeam Klystron

In this paper, a novel slow-wave structure (SWS) called folded V-shape groove waveguide SWS is proposed. The high frequency characteristics of this SWS is studied. An input and output waveguide transition structure, which is appropriate for this new kind of SWS is put forward. The transmission loss of the folded V-shape groove waveguide is lower than that of folded rectangular groove waveguide. The dimension of the folded V-shape groove waveguide is larger than that of the folded rectangular groove waveguide at the millimeter waveband, even at terahertz waveband. Based on this kind of SWS, a W-band sheet beam traveling-wave tube is studied, whose beam-wave interaction is calculated by means of the simulation software. The calculation results show that the output power can be over 260 W within 3-dB bandwidth from 84 to 98 GHz, the gain can reach up to 36 dB, and the electron efficiency is 12.33% at the center frequency.

Investigation on Sheet Beam Folded V-Shape Groove Waveguide for Millimeter-Wave TWT

The Institute of Electronics, Chinese Academy of Sciences, started developing X-band multibeam klystrons (MBKs) in 2000. Three types of X-band MBKs are currently under research and development; two types operate in the fundamental mode (TM010), and the other type operates in a high-order mode (coaxial TM310). These MBKs operate over the frequency range from 8 to 10 GHz and have peak powers of 50-100 kW, average powers of 2.5-5 kW, and bandwidths of 5%. The design considerations and testing results are presented in this paper. The technological problems, including nonhomogeneity of the RF electric field and low beam transmission, are also described. Further research work on the improvement of these MBKs is discussed.

Research Progress on X-Band Multibeam Klystron

Summary form only given. Results are reported for a 1.3 GHz, 10 MW multiple beam klystron that is being developed for the TESLA linear accelerator facility. It features six off-axis electron beams which are contained in a common enclosure, common and higher-order-mode input and output cavities, conventional klystron intermediate cavities with external tuners, dual waveguide and window outputs and six isolated collectors for the measurement of intercepted beam current on each beam line. The design parameters for the device are 10 MW peak RF output power with 150 kW average power, 1.5 ms pulse length, 65% efficiency, 50 dB gain, 4 MHz 1 dB bandwidth, 114 kV beam voltage, 131 A total beam current (emitted by the six cathodes) and 2.0 A/cm/sup 2/ maximum cathode loading.

Operation of a 1.3 GHz, 10 MW multiple beam klystron

A high efficiency multiple beam klystron, designated the VKL-8301, is being developed for the DESY superconducting linear accelerator TESLA in Hamburg, Germany. The accelerator will require 572 klystrons each producing up to 10 MW of rf output power at 1300 MHz. A multiple beam klystron will be used due to its ability to produce large rf output powers using moderate electron beam energies.

Development of a 10 MW, L-band multiple beam klystron for TESLA

IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established their position as reliable and highly efficient UHF amplifiers, predominantly in the television transmitter service. In this application, they reach output power levels equivalent to about 50 kW CW. Scientific applications, like proton accelerators, require UHF amplifiers with considerably higher output power capability. Super power klystrons are available for this service; however, IOTs offer some advantages over klystrons in terms of efficiency: higher basic efficiency; power regulation possible at full output power (no saturation); inconsequential drop of efficiency at reduced output power. Higher order mode IOTs (IOM-IOTs) possess the added advantage of lower operational voltage and smaller size. Based on these expectations, a development of a 700 MHz HOM-IOT, sponsored by the Los Alamos National Laboratory, has been carried out by CPI. The development attention was paid to the suppression of both unwanted modes and stray radiation from the space between electron gun and body. Focusing the electron beam was another issue that required high modeling effort.

700 MHz HOM-IOT: design and first test results

CPI has designed and is currently in the process of building a prototype of a horizontally oriented, ≥10 MW, ≥65% efficiency multiple beam klystron (MBK) operating at 1300 MHz. The klystron, designated the VKL-8301B, was ordered by DESY for the European XFEL. The klystron was designed using of sate-of-the-art multi-dimensional design codes to ensure that all performance requirements are exceeded. Initial rf hot test data at reduced duty and pulse width produced a peak saturated rf output power in excess of 11 MW and 70% efficiency, which was however accompanied by high beam interception. Operation at full duty and pulse width as well as adjustment of the focusing and retuning the cavity frequencies impacted output power and efficiency. A compromise was found to satisfy all required operating conditions, including operation into a higher output mismatch. Complete test results will be presented at the conference.

Design and operation of a high power, high efficiency, L-band multiple beam klystron

In this paper, we reported on the design of a 10 MW, 1300 MHz multiple beam klystron for TESLA superconducting linear accelerator. The multiple beam klystron is used in the accelerator because of its ability to produce high RF output power at moderate electron beam energies. The beam optics design has been verified by fully 3D simulations using the codes Michelle and Mafia. Electron trajectories in the gun region as calculated from Mafia codes.

Design of a multiple beam klystron for TESLA

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