Millimeter-wave Vacuum Electron Devices Research Articles

Limitations on Current of a Solid Axially Symmetric Electron Beam in the Drift Tubes of Millimeter-Wave Vacuum Electronic Devices

Conditions for ensuring the equilibrium stationary state of high-density solid electron beams, transported in cylindrical drift tubes and focused by uniform magnetic field, are investigated. Calculation results are compared to data obtained using the quasi-three-dimensional Arsenal-MSU computer code and analytical formulas proposed by other authors.

Current Limitations for the Axially Symmetric Hollow Electron Beam in the Drift Tubes of Millimeter-Wave Vacuum Electronic Devices

The conditions for ensuring the equilibrium steady-state of a high-density hollow electron beam transported in cylindrical drift tubes and focused by a uniform magnetic field are investigated. The results of numerical calculations of the currents limited due to the longitudinal deceleration of electrons by the space charge and the violation of equilibrium transverse magnetic focusing conditions when transporting beams of different configurations in klystron-type devices are presented. The limitations of the working length of the device associated with the excitation of diocotron instability are estimated. The calculation results were compared with the data obtained by the quasi-3D Arsenal—MSU computer code and by the approximate analytical formulas of other authors.

Limitations on Currents in Cylindrical Drift Tubes of Millimeter-Wave Vacuum Electronic Devices

The conditions providing the equilibrium stationary state of high-density solid and annular electron beams, transported in cylindrical drift tubes and focused by a homogeneous magnetic field, have been investigated. An efficient numerical model is proposed to determine the distributions of the electrostatic potential, charge density, and electron velocities in the stationary state of these beams, with allowance for the space-charge forces. The results of the numerical calculations for the limiting currents, determined by the longitudinal deceleration (caused by space-charge forces) and conditions for equilibrium transverse magnetic focusing for transported beams of different configurations on the length of a klystrontype vacuum electronic device, are presented. The limitations on the device working length, related to the excitation of diocotron instability, are estimated. The calculation results are compared with the data obtained using the quasi-three-dimensional program “Arsenal-MSU” and analytical formulas suggested by other researchers.

Practical Aspects of EIK Technology

Significant progress in modeling and manufacturing technologies open wide possibilities for performance improvements of millimeter-wave vacuum electron devices. However, many practical aspects should be considered to realize reliable long-life high-power sources. These are: thermal and RF stability, materials and assembly sensitivity to manufacturing, electrical stresses, cathode poisoning prevention, thermal beam effects, and many others. We address the full spectrum of design and manufacturing aspects while developing state-of-the-art extended interaction klystrons (EIKs). EIKs provide unprecedented RF performance and reliability in a compact user-friendly package. This paper discusses EIK design methodology and manufacturing concepts stating self-imposed restrictions and design modifications enhancing power capability, bandwidth, and extending operating frequencies into the terahertz region.

Research on equivalent circuit of multi-gap output cavity for sheet beam extended-interaction klystron

Sheet beam extended interaction klystron, which has both the advantages of sheet beam klystron and extended-interaction klystron (EIK), has become a key technique for developing high power microwave and millimeter-wave vacuum electron devices. An equivalent circuit of the five-gap output cavity for sheet beam EIK is proposed in this paper. The mode, resonant frequency, and the cavity impedance can be calculated by using the method of equivalent circuit efficiently. The bandwidth could be estimated by the curve of cavity impedance versus frequency. The influences of coupling coefficient (k) and external Q (Qe) on mode frequency interval and bandwidth are discussed. In order to test and verify the method of equivalent circuit, the 3D-PIC simulation of output cavity is conducted. The bandwidths under different values of external Q are calculated in two ways. The results accord well with each other. It is confirmed that the method of equivalent circuit for sheet beam EIK is accurate and credible. This is useful for the design of the whole tube.

Investigation on focus and transport characteristics of high transmission rate sheet electron beam

The investigation on focus and transport characteristics of sheet electron beam has been a key technique for the development of high-power microwave and millimeter-wave vacuum electronic devices. Compared with the period permanent magnetic system to transport the sheet electron beam, the uniform magnetic focusing system has many advantages, such as easily adjusting and matching the magnet with the beam, focusing the intensity electron beam, no cut off beam voltage restriction, etc. However, the Diocotron instability of the sheet electron beam in the uniform magnetic field can produce the distortion, deformation, vortex and oscillation to destroy the beam transportation. In this paper, the single-particle model and the cold-fluid model theory and calculation are used to indicate that if the electron optics system parameters of the sheet beam are designed more carefully, the magnitude of uniform magnetic field and the filling factor of the beam in transport tunnel are increased appropriately, the Diocotron instability can be reduced, even vanished completely to transport the sheet beam effectively in a long distance. To verify the above conclusion, the electron gun with the ellipse cathode and the electron optics system are designed and optimized with the three-dimensinal simulation software in detail. After the complex assembly and weld process with the small geometry and high precision, the W-band sheet electron beam tube is manufactured and tested. The sheet beam cross section of 10 mm0.7 mm is achieved experimentally with the one-dimensional compression and formation of electron gun. Also, with a beam voltage of 2080 kV, and beam current of 0.644.60 A,the experimental transmission rate of sheet beam electron tube manufactured is more than 95% with a drift length of 90 mm, which is higher than the periodic cusp magnetic field transport experiment result of 92% obtained recently.