Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Theory and Design of Charged Particle Beams

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2016 terahertz science and technology roadmap

Bibliometric data set the scene by illustrating the growth of terahertz work and the present interest in terahertz science and technology. After locating terahertz sources within the broader context of terahertz systems, an overview is given of the range of available sources, emphasizing recent developments. The focus then narrows to terahertz sources that rely on surface phenomena. Three are highlighted. Optical rectification, usually thought of as a bulk process, may in addition exhibit a surface contribution, which, in some cases, predominates. Transient surface currents, for convenience often separated into drift and diffusion currents, are well understood according to Monte Carlo modelling. Finally, terahertz surface emission by mechanical means—in the absence of photoexcitation—is described.

https://iopscience.iop.org/article/10.1088/0022-3727/47/37/374001/pdf

A review of terahertz sources

This paper presents a comprehensive theory of the cyclotron resonance maser (CRM) interaction in a circular waveguide. The kinetic theory is used to derive the dispersion relationships for both TE and TM modes. The TE mode case has been investigated by several authors, but there has been comparatively little work on the TM mode case. However, the TM mode interaction competes effectively with the TE mode interaction at relativistic electron energies. The conditions for maximum temporal and spatial growth rates are shown. The TM mode growth rates are found to vanish when the RF wave group velocity equals the beam axial velocity (‘grazing incidence’). The single particle theory is used to derive a compact set of self-consistent non-linear equations for the TE and TM mode interactions. These equations are particularly appropriate for the cyclotron auto-resonance maser (CARM) regime but applicability extends to other regimes as well. The conditions for optimum efficiency are investigated for oscillator and amp...

Linear and nonlinear theory of the Doppler-shifted cyclotron resonance maser based on TE and TM waveguide modes

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

The open rectangular grating with step-loaded slow-wave structure (SWS), a type of allmetal SWS for high power wide band mm-wave wave traveling wave tubes (TWT) is presented in this paper. By using the jumping conditions at the interface of two neighboring steps and single-mode approximation (SMA) field matching theory, the dispersion equation and coupling impedance of this SWS were obtained. Then the obtained complex dispersion equation was numerically calculated, and the slow-wave characteristics of the fundamental wave of this structure were discussed. Moreover, the calculation results by our theory were accordant with the simulation data obtained by the 3D electromagnetic simulation software HFSS. The numerical calculation results show that the dispersion characteristics and coupling impedance are notably improved by loading the steps. And the working bandwidth may be the widest when the thickness of the step is about equal to the thickness of the groove depth. The proper design parameters can be optimized to meet the needs of high frequency characteristics with wide bandwidth and high output power. The present study will be useful for further research and design of this kind of high frequency system.

Analysis of Step-Loaded Open Rectangular Grating Slow-Wave Structures for MM-Wave Traveling-Wave Tubes

In this paper, the effects of these structure parameters variations on performances of TWT are investigated. Therein, the working voltage can be determined from the dispersion curve of the slow-wave structure, as shown in Fig. 2, and the amplitude-frequency characteristics can be predicted from the frequency spectrums of input and output power, as shown in Fig. 3 and Fig. 4, by particle-in-cell (PIC) simulations. These results will favor the design of the circularly polarized traveling-wave tube.

Effect of structure parameter variations on performances of TWT with twisted twin comb

Summary form only given, as follows. Helical-Groove waveguide(HGW) traveling wave tube (TWT) is one of the potential alternative candidates for high power millimeter wave sources. In this paper, we present the analysis of the novel helical-groove waveguides, the conductor-centered arbitrarily-shaped helical-groove structures, for a possible employment in a wide band TWTs in slow-wave regime. By making use of field theory and admittance, the dispersion relation, interaction impedance are derived. Numerical analysis has performed with HGW-2[3] code to investigate the physical parameters including the groove shape, the radius of the center rod on the wave properties of the electromagnetic (EM) wave propagating through the conductor-centered arbitrarily-shaped helical-groove structure. As it shown from the dispersion characteristics, the profile of the groove takes large influence on high cut-off frequency, passband and wave velocities. This analysis also shows the interaction impedance and small signal gain of TWT with the variation of the physical parameters, indicating the bandwidth of HGW-TWT can be increased largely by choosing a conductor-centered arbitrarily-shaped helical-groove structure with a triangle profile of the groove.

Conductor-centered arbitrarily-shaped helical-groove slow-wave structure for TWTs

A general theory has been developed to account for the effect of the dielectric loss of discrete dielectric rods on traveling wave tube helix loss. It is clearly shown that the influence of dielectric loss on attenuation constant is much larger at the millimeter frequency band than that at the microwave frequency band. The general theory developed here has been further conformed by comparing the results with those obtained elsewhere for some special cases.

Theoretical Determination of TWT Helix Loss

In this paper, multiphysics field simulation is applied to analyze the temperature distribution of Ka-band U-shaped microstrip line planar TWT considering the thermal losses induced by ohmic loss and electron collision losses. The beam-wave interaction of the planar TWT is analyzed by using CST particle-in-cell (PIC) solver, at the same time the thermal losses distribution is recorded, which will be the heat source. The simulation results show that the high temperature with a peak value of 263 °C.

Yanyu Wei

Papers

Analysis of Step-Loaded Open Rectangular Grating Slow-Wave Structures for MM-Wave Traveling-Wave Tubes

Effect of structure parameter variations on performances of TWT with twisted twin comb

Conductor-centered arbitrarily-shaped helical-groove slow-wave structure for TWTs

Theoretical Determination of TWT Helix Loss

Multiphysics analysis of Ka-band U-shaped microstrip line planar traveling wave tube