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

We present an extension of the klystron simulation code TESLA to model multiple-beam klystrons (MBKs) in which interaction parameters may vary significantly from beam-tunnel to beam-tunnel. In earlier work, the single-beam code was applied to model the MBK by assuming that all electron beams and beam-tunnels were identical and all electron beams interacted identically with the fields of the resonant cavities, using averaged values of R/Q to represent interaction with each resonant cavity. To overcome the limitations of this approach and to take into account the effects from nonidentical beams and/or beam-tunnels, we have modified the code to use a parallel algorithm for multiple beams. The implementation of the parallel version of TESLA is based on the latest Fortran-95 version of the serial code and uses the message-passing interface library for communication. For testing and verification purposes, the new version of the code is applied to simulate an experimental four-cavity, eight-beam klystron amplifier, which was designed and successfully tested last year at the Naval Research Laboratory. The results of modeling using the new parallel TESLA and their comparison with experimental data are discussed in detail.

Parallel Simulation of Independent Beam-Tunnels in Multiple-Beam Klystrons Using TESLA

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

A strong candidate for the Standard Model Scalar boson, H(126), has been discovered by the Large Hadron Collider (LHC) experiments. In order to study this fundamental particle with unprecedented precision, and to perform precision tests of the closure of the Standard Model, we investigate the possibilities offered by An e+e- storage ring collider. We use a design inspired by the B-factories, taking into account the performance achieved at LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34 cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km circumference. The achievable luminosity increases with the bending radius, and for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision points appears feasible. Beamstrahlung becomes relevant at these high luminosities, leading to a design requirement of large momentum acceptance both in the accelerating system and in the optics. The larger machine could reach the top quark threshold, would yield luminosities per interaction point of 10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W pair production threshold (80 GeV per beam). The energy spread is reduced in the larger ring with respect to what is was at LEP, giving confidence that beam polarization for energy calibration purposes should be available up to the W pair threshold. The capabilities in term of physics performance are outlined.

A High Luminosity e+e- Collider to study the Higgs Boson

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 10 MW, 1.3 GHz multiple beam klystron (MBK) has been developed for the DESY X-FEL and International Linear Collider projects. The device uses six electron beams set off-axis on a large bolt circle which interact with a combination of higher-order-mode and conventional klystron cavities to efficiently produce high power RF. Extensive two and three dimensional simulations were used to design the device. Recent test results have validated the basic design concepts and procedure. Ten megawatts of peak and 150 kW of average power have been stably generated with 59% efficiency and 48 dB of gain.

/pdf/design-and-operation-of-a-high-power-l-band-multiple-beam-39mn6kdbi6.pdf

Design and Operation of a High Power L-Band 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

Summary form only given, as follows. A high efficiency multiple beam klystron (MBK) is being developed for the superconducting linear accelerator TESLA. 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.

/pdf/development-of-a-10-mw-l-band-multiple-beam-klystron-for-5z3gn2gyew.pdf

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

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Operation of a 1.3 GHz, 10 MW multiple beam klystron

Design and Operation of a High Power L-Band Multiple Beam Klystron

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

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

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