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

A 340GHz backward wave oscillator (BWO) based on the sine waveguide and pencil electron beam is presented as a novel terahertz radiation source. The particle-in-cell (PIC) simulation results predicts that this device can produce the output power of over 2.7W in the frequency range of 335.8–348.5GHz by utilizing a 20mA pencil beam and adjusting the voltage from 12kV to 14 kV.

A 340GHz sine waveguide backward-wave oscillator

The present study develops a dual-beam flat-roofed sine waveguide slow wave structure (SWG SWS) by complying with the conventional flat-roofed SWG SWS in this article. Through the placement of a metal plate in the electron beam tunnel center of conventional flat-roofed SWG SWS, the electron beam tunnel is divided into two tunnels. The SWS exhibits a wide working bandwidth, low loss, and small reflection by optimizing the structural size of the dual-beam flat-roofed SWG. Moreover, a comparison is drawn of the slow wave characteristics and beam–wave interaction between dual-beam flat-roofed SWG and conventional flat-roofed SWG. As revealed from the results, the output power level of the dual-beam flat-roofed SWG traveling-wave tube (TWT) is significantly higher than that of the flat-roofed SWG TWT exhibiting the identical current density or the input power. Furthermore, this study develops a $W$ -band high-gain dual-beam flat-roofed SWG TWT with an attenuator. The maximum output power is 756.6 W at 93 GHz, and the corresponding gain is 38.73 dB. In the frequency range of 89–100 GHz, the output power reaches over 500 W, and the 3-dB bandwidth exceeds 10 GHz.

Study on a Novel Dual-Beam Flat-Roofed Sine Waveguide Traveling-Wave Tube

The analysis of the novel coupled-cavity traveling-wave tube(CC-TWT) operating at X-band is presented for the purpose of gaining higher power with a smaller size compared with the existing coupled cavity circuit. The electromagnetic characteristics, and the beamwave interaction based on the ridge-loaded staggered single-slot rectangular coupled-cavity slow-wave structure(SWS) are investigated. Compared with the existing staggered single-slot rectangular coupled cavity TWT, our designed TWT has the advantage in coupled impedance and electron efficiency, which makes it has the potential of miniaturization in CC-TWT. The calculation results reveal that it can produce saturated output power over 23 kilowatts from 8.6 to 9.5GHz when the cathode voltage are set from 25.9kV to 26.9kV and beam current is 5A, respectively. The corresponding saturated gain and electron efficiency can reach over 39dB and 17.4%.

Ridge-Loaded staggered single-slot rectangular coupled-cavity structure for X-band traveling-wave tube

A Q-band high efficiency helix traveling wave tube (TWT) is designed and simulated in this paper. By using appropriate slow wave structure and taking reasonable helix pitch tapering method, high electronic efficiency and output power can be obtained. The 3D electromagnetic simulation software CST is used for the calculation of the high frequency characteristics and beam-wave interaction. The preliminary simulation results show that no oscillation is observed in the output signal. The electronic efficiency of this helix TWT exceeds 25.8% within the frequency range of 37-42.5GHz, the output power is more than 220W, and the gain is greater than 51dB.

Design of a Q-Band High Efficiency Helix TWT

We present a novel double V-shaped winding microstrip meander-line slow-wave structure (SWS) for traveling-wave tubes (TWTs) in this paper. The proposed structure evolves from a V-shaped winding microstrip meander-line. The radio-frequency characteristics of the above-mentioned structures are calculated. Numerical results from high frequency characteristics calculation are given and analyzed. It has been illustrated that, compared with the V-shaped winding microstrip meander-line, the novel structure proposed in this paper has higher interaction impedance and the same cold bandwidth over the working frequency band.

Yanyu Wei

Papers

A 340GHz sine waveguide backward-wave oscillator

Study on a Novel Dual-Beam Flat-Roofed Sine Waveguide Traveling-Wave Tube

Ridge-Loaded staggered single-slot rectangular coupled-cavity structure for X-band traveling-wave tube

Design of a Q-Band High Efficiency Helix TWT

A novel double V-shaped winding microstrip meander-line slow wave structure for millimeter-wave TWTs