Oleg A. Nezhevenko

Design of a high power X-band magnicon amplifier

We present a design study for an X-band frequency-doubling magnicon amplifier driven by a 500 keV, 172 A beam from a field-emission diode. This study makes use of steady-state particle simulations employing the realistic fields of magnicon cavities connected by beam tunnels, and includes the effects of finite electron beam diameter. The simulations propagate an electron beam through a sequence of deflection cavities at 5.7 GHz, followed by an output cavity that operates at 11.4 GHz. The deflection cavities and the output cavity contain synchronously rotating TM modes. The deflection cavities progressively spin up the beam transverse momentum, until /spl alpha//spl equiv/v/sub /spl perp///v/sub z/>1, where v/sub /spl perp// and v/sub z/ are the velocity components perpendicular and parallel to the axial magnetic field. The output cavity uses this synchronously gyrating beam to generate microwave radiation at twice the drive frequency. Self-consistency of the simulation is achieved by iteration until power balance exists in each cavity, and until the optimum RF phase in each cavity is determined. The final magnicon circuit should produce 20 to 50 MW at 11.4 GHz, depending on initial beam diameter, with a drive power of 1 kW at 5.7 GHz. >

Commissioning of the 34-GHz, 45-MW pulsed magnicon

A high-efficiency, high-power magnicon at 34.272 GHz has been designed and built as a microwave source to develop radio frequency (RF) technology for future multi-TeV electron-positron linear colliders. To develop this technology, this new RF source is being perfected for necessary tests of accelerating structures, RF pulse compressors, RF components, and to determine limits of breakdown and metal fatigue. The design of this high-power amplifier tube, as well as the first experimental results are presented.

X-band magnicon amplifier for the Next Linear Collider

The magnicon is a scanning-beam microwave amplifier that is being developed as a high power, highly efficient microwave source for use in powering the next generation of high gradient electron linear accelerators. This article first discusses the results from a cold cathode magnicon experiment at 11.12 GHz, driven by a single-shot Marx generator. Following this, a design is presented for a new thermionic magnicon experiment to produce more than 50 MW at 11.4 GHz, using a 210 A, 500 kV beam from an ultrahigh convergence thermionic electron gun driven by a repetition-rated modulator. This new design has a predicted efficiency in excess of 60%.The magnicon is a scanning-beam microwave amplifier that is being developed as a high power, highly efficient microwave source for use in powering the next generation of high gradient electron linear accelerators. This article first discusses the results from a cold cathode magnicon experiment at 11.12 GHz, driven by a single-shot Marx generator. Following this, a design is presented for a new thermionic magnicon experiment to produce more than 50 MW at 11.4 GHz, using a 210 A, 500 kV beam from an ultrahigh convergence thermionic electron gun driven by a repetition-rated modulator. This new design has a predicted efficiency in excess of 60%.

High power pulsed magnicon at 34-GHz

A high efficiency, high power magnicon amplifier at 34.272 GHz has been designed as a radiation source to drive multi-TeV electron-positron linear colliders. Simulations show peak output power of 45 MW in a 1.5 microsecond wide pulse with an efficiency of 45% and gain of 55 dB. The repetition rate is 10 Hz. The amplifier is a frequency tripler, or third harmonic amplifier, in that the output frequency of 34.272 GHz is three times the input drive frequency of 11.424 GHz. Thus the rotating TM110 modes in the drive cavity, 3 gain cavities and double decoupled penultimate cavities are resonant near 11.424 GHz; and the rotating TM310 mode in the output cavity is resonant at 34.272 GHz. A 500 kV, 200 A high area compression electron gun will provide a low emittance electron beam with a diameter of about 0.8 mm. A superconducting solenoid magnet will provide a magnetic field of 13 kG in the deflection system and 22 kG in the output cavity. A collector for the spent beam has also been designed. Detailed simulatio...

High-power high-convergence electron gun for an 11.424-GHz pulsed magnicon

This paper describes the design and testing of an ultrahigh-convergence electron gun that was developed for a high-power X-band magnicon amplifier. The gun operates at an area compression ratio of 1400:1 to produce a /spl sim/500-kV /spl sim/200-A beam with a diameter of /spl sim/2 mm.

High Power Accelerator R&D at the NRL 11.424‐GHz Magnicon Facility

An 11.424‐GHz magnicon amplifier has been jointly developed by the Naval Research Laboratory and Omega‐P, Inc. as an alternative technology to klystrons for powering a future X‐band linear collider. This paper will discuss its background, operating principles, and results to date, as well its present status as part of a facility for collaborative research on accelerator‐related technologies that require high‐power 11.424‐GHz radiation. Two collaborative research programs are currently under way using the magnicon output. The first, a collaboration with Omega‐P, Inc. and the Institute of Applied Physics, is investigating active microwave pulse compressors using plasma switch tubes. The second, a collaboration with Argonne National Laboratory and SLAC, is investigating dielectric‐loaded accelerating (DLA) structures, with the ultimate goal of developing a compact DLA accelerator.

Recent developments in high-power magnicons for particle accelerators

Continued progress in high energy and nuclear physics demands a new generation of particle accelerators, which in turn requires new high-power, high efficiency rf sources. One of the attractive candidates for this role is the magnicon–microwave amplifier with circular deflection of an electron beam. Magnicons have shown great potential with both high efficiency and high power. A first magnicon to have demonstrated these qualities was built and tested in the 80s in Novosibirsk. A power of 2.6 MW was obtained at 915 MHz with a pulse width of 30 μs and an electronic efficiency of 85%. The latest results in magnicon research, as well as the status of current magnicon projects, are presented in this paper. Examples of both operating magnicons and those under development include decimeter wave (1.3 GHz) amplifiers with a power level up to 10 MW in millisecond pulses; frequency-doublers in the centimeter wave range (7 GHz and 11.4 GHz) at a power of 50–60 MW, and a 40 MW frequency-tripler in the millimeter range...

Two-channel active high-power X-band pulse compressor

A two-channel active pulse compressor has been developed that is able to provide output-pulses of at least 100 MW peak power with pulse duration of 100 nsec at X-band, with a power gain of 12–15 and with an energy efficiency of 60%. This paper describes the design of the compressor and the driving generator-compressor microwave circuit. Each channel of the compressor is connected to the driving generator and the load via a novel 3-dB quasi-optical coupler. Variations in phase of compressed output pulses from this active pulse compressor were measured. The moderate-power tests of a prototype design of such a compressor using 100 kW-level microwaves demonstrated coherent addition of the compressed pulses from each of the compressor channels. The paper also describes design of a modified output reflector, with which the two-channel active pulse compressor can produce output pulses with a peak power of at least 500 MW and a power gain 12–15.

Compact all-metal high-vacuum gate valve for microwave tube research

A manually operated all-metal high-vacuum bakable gate valve is described that is designed to attach between an electron gun and an experimental high-power microwave tube. It is designed with a minimal radial extent in order to fit within the 20 cm bore of a magnet that encloses the microwave tube. It also provides a continuous cylindrical metal boundary condition for the electron beam. The valve is used to maintain the electron gun vacuum when the remainder of the tube is brought up to atmospheric pressure for modifications.

ACTIVE COMPRESSION OF RF PULSES

The active RF pulse compression is considered as a candidate for using in feed systems of future electron-positron colliders. The key component of the compressor is an electrically controlled switch changing one state for another in a time much shorter than the desired RF pulse width. For an X-band two- channel RF compressor based on TE01-mode energy storage cavities, a gas discharge switch is proposed. Designs, low- and high-power tests of some versions of the compressor are described in this paper. At high-power tests carried using the Omega-P/NRL 11.424 GHz magnicon, 50 MW compressed RF pulses have been produced. The application of developed plasma switches for an electrically controlled switching of an existing passive pulse compressor SLED-II for increasing its efficiency as proposed by SLAC is discussed. The low-power test of the plasma switch for X-band active SLEDII compressor is described.