We report on hot test measurements of a wide-bandwidth, 220-GHz sheet beam traveling wave tube amplifier developed under the Defense advanced research projects agency (DARPA) HiFIVE program. Nano-computer numerical control (CNC) milling techniques were employed for the precision fabrication of double vane, half-period staggered interaction structures achieving submicrometer tolerances and nanoscale surface roughness. A multilayer diffusion bonding technique was implemented to complete the structure demonstrating wide bandwidth (>50 GHz) with an insertion loss of about −5 dB achieved during transmission measurements of the circuit. The sheet beam electron gun utilized nanocomposite scandate tungsten cathodes that provided over 438-A/cm2 current density in the 12.5:1 ratio sheet beam. An InP HBT-based monolithic microwave integrated circuit preamplifier was employed for TWT gain measurements in the stable amplifier operation region. In the wide-bandwidth operation mode (for gun voltage of 20.9 kV), a gain of over 24 dB was measured over the frequency range of 207–221 GHz. In the high-gain operation mode (for gun voltage of 21.8 kV), over 30 dB of gain was measured over the frequency range of 197–202 GHz. High-power tests were conducted employing an extended interaction klystron.

Performance of a Nano-CNC Machined 220-GHz Traveling Wave Tube Amplifier

A millimeter (mm) wave amplifier that combines both high-power output and a wide bandwidth would enable dramatic improvements in areas where high-power radio signals with significant information content are required. However, to date, the only available devices are either high-power vacuum electronic devices with limited bandwidths, or larger bandwidth semiconductor amplifiers with low-power output. Here, we show a new design of a vacuum electronic traveling-wave tube amplifier that has a measured output power of 107 W with a 3-dB bandwidth of 6 GHz centered on 200 GHz. The power-bandwidth product of this amplifier is 642 W-GHz. These results provide a demonstration of a high-power mm-wave source with significant bandwidth. This device is readily scalable to other frequency bands, particularly those in the mm- and sub-mm-wave frequency bands from 100 GHz to 1 THz.

Development of a 100-W 200-GHz High Bandwidth mm-Wave Amplifier

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.

/pdf/high-power-klystrons-theory-and-practice-at-the-stanford-4pi6u2u4uw.pdf

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

In this paper, the cold-fluid model theory of an intense sheet electron beam is developed to investigate the diocotron instability during its transport in a uniform magnetic field. The model shows that if the magnetic field strength and the beam filling factor are increased separately, the diocotron instability will be suppressed, which extends the sheet-beam transport distance effectively. To verify the above conclusion, a set of complicated instruments, the electron beam measuring and analyzing system (EBMAS), was developed to measure the beam cross section, beam current density, and the 3-D trajectory. The sheet electron beam transport process in a uniform magnetic field with its diocotron instability is investigated on the basis of EBMAS measurements. The measured results agree very well with theoretical calculation and numerical simulation. A sheet-electron-beam tube based on a uniform magnetic field was then manufactured to drive a future W-band sheet-beam klystron (WSBK). Tuning the sheet-beam parameters over a broad range, including a cathode voltage range of 20–82 kV, current range of 0.5–4.27 A, and with a beam cross section of about 10 mm $\times\,$ 0.5 mm, the experimental beam transmission rate is above 98% through a beam tunnel of 100 mm in length.

Theoretical and Experimental Investigation on Intense Sheet Electron Beam Transport With Its Diocotron Instability in a Uniform Magnetic Field

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

PPM focusing has been used in a 2.5 MW, 9300 MHz klystron. The design will be discussed and test results for three klystrons presented.

Design and operation of a 2.5 MW, PPM focused X-band klystron

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

A compact periodic permanent magnet focused 9290 MHz klystron is described that produces 2.7 MW of output power with 52 dB of gain and 43% efficiency. Three klystrons have been manufactured that exhibited a high degree of repeatability and robustness with all meeting the performance requirements. The goal of a first-time-through design success was met through the use of extensive multidimensional modeling of all aspects of the klystron. Agreement between simulated and measured performance was very good.

Design and Operation of a 2.7 MW Periodic Permanent Magnet Focused X-band Klystron

The Goldstone Solar System Radar (GSSR), part of the Deep Space Network (DSN), utilizes a 70 meter antenna and a 500kW CW transmitter powered by two VKX-7864B, 250kW CW X-band (8560 MHz) klystrons. The VKX-7864B klystron, developed in 1988, required improvements in power output, bandwidth, and reliability to ensure long term system sustainability and to support demands of future DSN/GSSR critical missions. CPI reviewed klystron subassemblies historical failure modes, performed simulations with State-of-the-Art computer codes, and identified improvement opportunities. Improvements in the beam optics, RF circuits gain, bandwidth, and efficiency, collector dissipation, coolant flow, thermal stability, and mechanical reliability were implemented in a high reliability klystron upgrade, designated the VKX-7864C. All performance goals were met or exceeded. Power output > 250kW CW over entire 50 MHz bandwidth, gain > 51dB, efficiency > 45%, RF beam transmission > 99.99%. This paper presents some important improvements of this klystron development.

Upgrading the 250kW CW X-band klystron used in the goldstone solar system radar

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