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 flat-roofed sine waveguide for Ka-band traveling wave tube is designed in this paper, in order to analyze its beam wave interaction in such frequency band. For increasing the output power and suppressing oscillatory signal, this structure adopts the two-stage structure and the phase velocity jump technology. PIC method is used to analyze the beam wave interaction and the simulation results show that the model has the advantages of wide bandwidth and high output power. In the bandwidth of 32-36GHz, the output power of the structure is greater than 6000W, the gain is above 33.01dB, and the minimum electronic efficiency is 13%.

Design of Two-stage Flat-roofed Sine Waveguide SWS for a 6kW Level Traveling Wave Tube

An open-styled dielectric-lined azimuthally periodic circular waveguide (ODLAP-CW) which is a modified form of a dielectric-lined azimuthally periodic circular waveguide (DLAP-CW) is proposed in this paper. Here, the metal shell in the DLAP-CW is replaced by absorbing materials in the improved structure. The improved structure can effectively eliminate the mode competition in the beam-wave interaction with only slight influence on the dispersion characteristics. As a result, the interaction efficiency and the stability of the TWT based on such a structure can be expected to be greatly improved.

The research of an open-styled dielectric-lined azimuthally periodic circular waveguide for TWT

In this paper, based on a novel focusing structure, the characteristics of a W-Band microstrip meander-line traveling wave tube (MML-TWT) are simulated and analyzed. Compared with the traditional approach, the novel focusing structure can achieve the purpose of stable sheet electron beam (SEB) transport with lower magnetic field. The simulation results show that the novel focusing structure for MML-TWT is beneficial to balance the potential distribution and evidently reduce the operating magnetic field, while it barely affects the high frequency characteristics of the whole device. Furthermore, the lower magnetic field can contribute to a miniaturization of the bulkiness of the MML-TWTs.

Analysis of a W-Band Microstrip Meander-Line TWT with Novel Focusing Structure

A high-frequency structure that can be used for the G-band high-power traveling wave tube is proposed to analyz and the slow-wave characteristics of the quasi flat-roofed sine waveguide(QFRSWG). The PIC method is used to obtain the interaction characteristics of the sheet electron beam and the electromagnetic wave in this structure. The calculation results show that the traveling wave tube can produce over 110 W output power in the frequency range of 212 GHz-232 GHz, the gain is greater than 33.94 dB and the maximum electronic efficiency is 5.25 %.

Design of a 100-W 20-GHz Bandwith G-band TWT Based on Quasi Flat-roofed Sine Waveguide

2D material graphene has a wide range of applications in terahertz, most graphene modulation is performed with electrodes for gate voltage modulation or high-power laser pulse modulation. Here, we construct a self-developed system based on scanning electron microscopy (SEM) combined with terahertz time-domain spectroscopy (TDS) to experimentally demonstrate the tuning of a no-electrode graphene metamaterial modulation. Because the electron beam radius and position of the SEM is highly controllable, it can be adjusted precisely. This is of seminal importance for the development of terahertz graphene terahertz devices.

Yanyu Wei

Papers

Design of Two-stage Flat-roofed Sine Waveguide SWS for a 6kW Level Traveling Wave Tube

The research of an open-styled dielectric-lined azimuthally periodic circular waveguide for TWT

Analysis of a W-Band Microstrip Meander-Line TWT with Novel Focusing Structure

Design of a 100-W 20-GHz Bandwith G-band TWT Based on Quasi Flat-roofed Sine Waveguide

Accurate modulation of graphene metamaterials with no-electrode through free electrons