Periodic Permanent Magnet Focusing System Research Articles

Investigation of Spindt Cold Cathode Electron Guns for Terahertz Traveling Wave Tubes

In this work, a Spindt cold cathode electron gun with a PPM (periodic permanent magnet) focusing system for a terahertz TWT (traveling wave tube) was designed and simulated based on the Pierce electron gun structure. More specifically, a new 3D (three dimensional) emission model was used, where the cathode radius of the electron gun was 1 mm and the cathode current was 30 mA, with an emitting half angle of about 28°. It was demonstrated that the electron beam was well focused with an electron beam radius of 0.3 mm and a filling ratio of 0.5 when the maximum value of the PPM field along with the axis was 0.122T. According to the simulation results, a planar cold cathode electron gun was developed. Measurements demonstrated that the I/V characteristics of the cold cathode gun were consistent with that of a cold cathode, revealing that the electrons emitted from the cathode are not intercepted when passing through the electron gun.

Development of a compact coaxial cusped periodic permanent magnet focusing system.

To achieve the application of a periodic permanent magnet in high power microwave, a compact coaxial cusped periodic permanent magnet (CPPM) focusing system is constructed. The system consists of permanent magnets with different magnetization directions and soft magnets. Taking the required magnetic field performance and the effect of demagnetization into account, NdFeB and FeCoV are selected as the permanent and soft magnet materials. After the system is constructed, the magnetic field is measured. The results show that the guiding magnetic field strength and period of the CPPM are about 0.29 T and 26 mm, respectively, and the magnetic field distribution of measurement shows good agreement with the simulation results. However, there are some differences between the measurement and simulation results, and the differences are compared and analyzed here.

Temperature stability of magnetic field for periodic permanent-magnet focusing system

In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet (PPM) focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak (B z)max of single magnet ring is greater than that of remanence B r of magnet in the range from room temperature to 200 °C, however, the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less H cb, giving rise to lower magnetic induction peak \( ( {B_{\text{z}} })^{\prime }_{\hbox{max} }. \) Finally, it should be noted that the magnetic orientation deviation angle θ (<15°) of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.

Structure and magnetic field of periodic permanent magnetic focusing system with open magnetic rings

The magnetic field along the central axis for an axially magnetized permanent magnetic ring was investigated by analytical and finite element methods. For open magnetic rings, both calculated and measured results show that the existence of the radial magnetic field creates a remarkable cosine distribution field along the central axis. A new structure of periodic permanent magnet focusing system with open magnetic rings is proposed. The structure provides a satisfactory magnetic field with a stable peak value of 120 mT for a traveling wave tube system.

Application of high-temperature permanent magnets Sm(Co, Fe, Cu, Zr) Z in PPM focusing system

Rare earth permanent magnets Sm(Co, Fe, Cu, Zr) Z with outstanding performance and high-temperature thermal stability were fabricated. Optimized by Fe content and process, Sm(Co 0.72Fe 0.15Cu 0.1Zr 0.03) 7.5 magnet with B r>0.75 T and H ci>1300 kA/m at 300 °C can be obtained. According to the performance data of Sm(Co 0.72Fe 0.15Cu 0.1Zr 0.03) 7.5, the magnetic field along central axis B Z in periodic permanent magnet (PPM) focusing system was simulated using electromagnetic field analysis software Maxwell 2D/3D. The B Z exhibited typical cosine curve along central axis, and the peak value of B Z was high enough to meet the demand of PPM focusing system at room temperature even at 200±20 °C. Additionally, a kind of simple cooling structure for PPM focusing system was designed by setting cooling pipe between polepieces. Simulated results showed that smooth cosine curve of B Z was successfully achieved with good control of the thickness of cooling pipe.

Periodic permanent magnet focusing system with high peak field

In this study, hybrid periodic permanent magnet (PPM) system is studied, which has high axial magnetic field and low magnetic leakage. By simulation computation, some laws of magnetic field distribution vs. structure dimensions were obtained. A hybrid PPM is designed and constructed whose peak field reaches 0.6 T. The factors inducing discrepancies between computational results and practical measurements are analyzed. The magnetic field distribution is very sensitive to the variations of constructional parameters. Construction accuracy greatly influences the magnetic field distribution. Research results obtained here are potentially valuable for future work.

Dynamic defocusing of electron beams in high-power helical traveling-wave tubes with length-dependent dispersion

Dynamic defocusing in a wideband helical traveling-wave tube (TWT) with an output power of 1.5–2.0 kW in the continuous-operation mode is analyzed. The TWT contains fragments with normal and anomalous dispersion of the phase velocity. It is demonstrated that the TWT output characteristics can be improved and the TWT stability against self-excitation on the backward wave can be increased with the use of appropriate values of parameters of the electron-optical system that forms a converging axially symmetric beam focused by a periodic permanent-magnet focusing system.

S-Band Multibeam Klystron With Bandwidth of 10%

A new type of S-band multibeam klystron has been developed at the Institute of Electronics, Chinese Academy of Sciences, China. The main methods for obtaining wide bandwidth include a multibeam electron gun with 18 beams, a periodic permanent magnet focusing system, a wide-band bunching system and filter-load double-gap coupling-cavity output circuit. The design methods and experimental results are given in this paper. The test results show that this device has a peak power of 120-160 kW, a bandwidth of 10%, a gain of 41 dB, a beam voltage of 16 kV, a weight of 45 kg and a length of 700 mm.

A variable high-power multi-beam klystron design

We describe here a 1.497 GHz multi-beam klystron with up to 13 kW of continuous output power, greater than 60% efficiency, and stable linear operation at ∼10% below saturation, whose design is based on direct extrapolation from klystrons operating in our electron accelerators. The beam perveance is individually adjusted with a zero-current control-electrode gun to match the parameters of a specific application, such as superconducting accelerating structures. The 18 beams are guided through six toroidal cavities, five operating at the fundamental and one at the 2nd harmonic, by a reverse periodic permanent magnet focusing system.

Periodic permanent magnets-focusing super electron-beam ion trap (abstract)

An electron-beam ion trap (EBIT) has been built as an instrument for in situ studies of atomic physics with great success. But the high complexity of the superconducting EBIT limits its use at small laboratories. In this article we consider the Super EBIT with focusing of the electron beam by a periodic permanent magnets (PPM) system. The preliminary analysis shows that a PPM Super EBIT with electron energy 200 keV and electron density about 1000 A/cm2 can be built. We would like to note that this device, first of all, is inexpensive and useful, and there are no gas freeze layer ‘‘memory effects’’ on the inner walls that are important for some applications. The proposal design and some computer simulations of EBIT with a periodic permanent magnet focusing system are presented.

A periodically focused kilowatt level traveling-wave tube amplifier

A pulsed, kilowatt-level, S-band, traveling-wave tube amplifier is described which utilizes a periodic permanent magnet focusing system. A considerable saving in weight as well as the elimination of the magnet power supply is thereby achieved. The final packaged tube weighs less than ten pounds. A kilowatt level tube has previously been reported by Caldwell and Iversen. However, in order to incorporate periodic focusing into such a tube, an extensive redesign was necessary. A converging type electron gun is used; coupled helix transducers with a coupled-helix attenuator have been developed for use with the new focusing system. In addition to providing a compatible structure for use with a periodic focusing system, these changes have resulted in improved performance, particularly a wider bandwidth.