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

Recently, a new need for high-frequency, high-power sources has been emerging for advanced radar and communication needs, with frequencies in the band between 100 and 300GHz and peak powers as high as several hundreds of kilowatts, and with bandwidth of up to 10%. After investigation of the interaction mechanisms of different slow-wave structures, the rectangular waveguide grating SWS has attracted the scholar's interest due to some of its peculiarities: the scalability to smaller dimensions and shorter wavelengths, high precession of manufacturing and assembling, super thermal conductivity and low loss, which make it worth consideration, especially at millimeter-wave frequency-band. From the investigation of the different structures, such as V-type, cosine-type, dovetail-type, etc., the cosine-shaped groove SWS has the weakest dispersion and the widest bandwidth. In this paper, this type of structure was analyzed. A longitudinal cross section configuration is shown in Fig. 1. s is the width at the mouth of the groove, L is the period and L=s, b and p are waveguide height and groove depth, respectively. The width of the rectangular waveguide is represented by a. Expressed in terms of rectangular coordinates, the space of the rectangular waveguide grating SWS with cosine-shape grooves can be divided into two parts: interaction region I and groove region II. By means of an approximate field-theory analysis, the expressions of dispersion equation and coupling impedance are derived.

Study on Rectangular Waveguide Grating Slow-Wave Structure with Cosine-Shaped Grooves

The backward wave oscillator (BWO) is one of the best choices for generating high-power radiation waves in the terahertz (THz) region. In order to improve the efficiency of beam–wave interaction and output power, a novel THz BWO scheme is proposed in this article, which uses double-slot embedded electron beams (DSEEB) to drive a grating loaded rectangular waveguide (GLRW) slow wave structure (SWS). The dispersion relation and the coupling impedance of the proposed SWS are derived by using an eigenfunction method (EFM) and solved with a numerical method. The results show that the upper limit frequency and the coupling impedances are remarkably improved, which are greater than those of traditional grating SWS. Based on this scheme, a BWO operating at the frequency of 0.5 THz is designed. The particle-in-cell simulations show that the output power reaches 8.86 W with an efficiency of 0.9%, which is 2.5 times the electronic efficiency of the conventional BWO. Thus, the proposed scheme provides a promising aim to develop the high-power THz source, which may be used in THz biomedical and material studies, and so on.

An Efficiency-Enhanced 0.5-THz BWO Using Double-Slot Embedded Electron Beams to Drive a Grating Loaded Rectangular Waveguide

This paper pertinently investigates the Backward wave oscillator (BWO) based upon a novel sine-shaped ridge waveguide (SSRWG) slow wave structure (SWS) which works in the frequency range of 300-350GHz. The dispersion characteristics and interaction impedance of SSRWG and normal sine waveguide (SWG) are compared. The results show that SSRWG has a wider bandwidth at the same size and a higher interaction impedance at the same phase velocity than those of SWG. The beam-wave interaction is then simulated by CST Particle Studio. The results show that this BWO loaded by pencil electron can produce more than 2.5W output power in 300-350GHz frequency range.

A Wideband 340GHz Backward Wave Oscillator with Sine-Shaped Ridge Waveguide Slow Wave Structure

The development of 220GHz sine waveguide BWO with cylindrical beam tunnel is presented here. The particle-in-cell (PIC) simulation result predicts that this device can product the output power over 6.SW in frequency range of 214.07GHz to 224.99GHz. The radius of beam tunnel is 0.2 mm. The beam current is chosen as 70mA which has a current density of 99A/cmA2. The uniform magnetic is 0.25T.

220GHz Sine Waveguide BWO with large Beam Tunnel

A double flat-roofed sine waveguide (DFRSWG) slow wave structure (SWS) with low loss for 220-GHz traveling-wave tube (TWT) has been demonstrated in this letter. Through the simulation method, it is inferred that this structure has a large coupling impedance and excellent transmission properties. Besides, the experimental results demonstrate that the transmission loss of the circuit is only 0.62–0.75 dB/cm and the return loss is more than 19.3 dB in the frequency band of 210–250 GHz. Eventually, a two-section DFRSWG interaction circuit is designed to achieve stable device performance. Based on the particle-in-cell (PIC) simulation results, it can be predicted that the DFRSWG TWT can generate the maximum output power of 235 W at 220 GHz, which corresponds to a gain of 36.72 dB and an electronic efficiency of 6.06%.

Yanyu Wei

Papers

Study on Rectangular Waveguide Grating Slow-Wave Structure with Cosine-Shaped Grooves

An Efficiency-Enhanced 0.5-THz BWO Using Double-Slot Embedded Electron Beams to Drive a Grating Loaded Rectangular Waveguide

A Wideband 340GHz Backward Wave Oscillator with Sine-Shaped Ridge Waveguide Slow Wave Structure

220GHz Sine Waveguide BWO with large Beam Tunnel

Demonstration of a Double Flat-Roofed Sine Waveguide Slow Wave Structure With Low Loss for 220-GHz Traveling-Wave Tube