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A surface-wave oscillator (SWO) is one of the promising terahertz-wave sources based on excitation of a surface wave using an electron beam. The surface wave is formed by a metal periodic structure, and the frequency is determined by the size parameter of the structure and the parameters of the electron beam. In this article, we design and fabricate a 200-GHz cylindrical corrugated waveguide which has the periodic structure on the inner wall. The field intensity of the surface wave rapidly decreases to zero from the structured wall. Due to a manufacturing error of the corrugated waveguide, the frequency of the surface wave in the fabricated structure decreases to 189 GHz at $\pi $ -point in comparison with the frequency of 204 GHz in the designed one. The effect of the error is evaluated by calculating the intensity distribution of the electric field of the surface wave and its growth rate due to the beam interaction. We also conduct the SWO experiment using the fabricated waveguide. Intense radiation with a total power is roughly estimated to 0.2 kW with a 45-keV and 60-A electron beam.

Spoof plasmon is surface waves extended along corrugated surfaces and the terahertz equivalent of optical surface plasmon polaritons for metals. The spoof plasmon may be effectively excited by an electron beam. The beam is perturbed three-dimensionally during the interaction with the spoof plasmon. In this work, we present numerical analysis on the spoof-plasmon instability driven by a magnetized electron beam in a terahertz region. The slow cyclotron as well as Cherenkov instabilities of the spoof plasmon are excited due to the 3-D perturbation. The two instabilities grow large and merge by increasing the beam current and decreasing the magnetic field. The merged instability divides again into the two instabilities for an extremely high beam current. The spoof-plasmon instabilities are examined by revealing modes involved using the saddle-point analysis.

We studied the operation of an oversized backward wave oscillator driven by an electron beam with energy less than 100 keV for terahertz radiation. Cylindrical slow wave structures (SWSs) with rectangular corrugations and annular electron beam are used to generate broadband terahertz radiation. The starting conditions for intense terahertz radiation are examined by varying the beam parameter and the SWS length. Operation frequencies in the range of 0.26–0.34 THz and 0.31–0.39 THz are obtained using two types of SWSs with different corrugation amplitudes. The obtained maximum output power is at the kilowatt level. Characteristics of the beam instabilities in the terahertz-SWSs are examined by comparison between the experimental and numerical results.

We numerically and experimentally studied the operation of a W-band (75–110 GHz) surface-wave oscillator driven by the electron beam energy of less than 100 keV. Two numerical methods of the real wavenumber analysis and the saddle point analysis are studied to examine the operation of the oscillator. We analyzed the Cherenkov instability for the interaction of the space charge modes and the structure modes EH01. We showed that the instabilities are of absolute instabilities when the oscillator operates around the $\pi $ -point region. In the experiment, radiations due to the absolute instability are detected around the $\pi $ -point region when the length of the slow-wave structure (SWS) is short enough. On the other hand, the absolute instability generates no meaningful radiation in the $\pi $ -point region for the long length of SWS.

Beam interactions with surface waves and higher order modes in oversized $G$ -band slow-wave structures (SWSs) are studied in a coaxial SWS. The coaxial SWS reduces the number of higher order mode and eases the mode competition problem. The SWS is excited by an annular electron beam. The slow cyclotron (SC) interaction as well as the Cherenkov interaction occurs due to 3-D beam perturbations of the electron beam. Growth rates for the surface waves are larger than those for the higher order modes and increase with increasing beam current. The SC interaction merges with the Cherenkov interaction for a sufficiently high beam current and a relatively low magnetic field. And the merged growth rate also increases with the beam current.

We have studied an atmospheric-pressure plasma generated using a quartz tube, helium gas, and a copper foil electrode by the application of a radio-frequency high voltage. The atmospheric-pressure plasma, which is generated in the form of a bullet, is released as a plume into the atmosphere. To study the properties of plasma plume formation, we examine the relationships among the plasma plume length and charge and the applied voltage waveform. The dependences of the waveform on the plasma plume length and charge are not clear. However, the plasma plume length increases with increasing plasma plume charge in laminar flow. Consequently, we find that the plasma plume length depends on the plasma plume charge becoming an energy source so that electric charge travels the plasma.

An oversized $G$ -band backward wave oscillator (BWO) driven by a weakly relativistic electron beam less than 100 kV is studied. Rectangular corrugations are used as the slow-wave structure (SWS), which have surface waves with upper cutoff frequencies of above 150 GHz [ $G$ -band (140–220 GHz)]. In this paper, we examine the starting conditions for intense $G$ -band BWO operation by varying the beam parameters and SWS lengths. It is shown that a starting energy exists for the $G$ -band BWO and that the starting energy is more critical than the starting current in the oversized BWO. Above the starting energy, very intense output powers on the order of 10 kW are obtained. The oscillation-starting condition for such intense operation may play an important role in high-intensity terahertz wave sources.

We present a measurement method of the plasma current and density in an atmospheric-pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying a high RF voltage. The plasma in the form of a bullet is released as a plume or jet into the atmosphere. To study the characteristics of the atmospheric-pressure plasma, the plasma current is measured using a current probe, and the drift velocity of plasma plume is measured using a photodetector. The current of the plasma plume is estimated by subtracting the ground line current from the power line current in the circuit. The density of plasma plume n is estimated from the plasma plume current I and the drift velocity v as I = envS, where S is the cross section of plasma plume. The density of the released plasma into the atmosphere is estimated as ∼1018 m−3 by the method. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Possible legacy of the Tokyo 2020 Paralympics can broadly be divided into two parts: domestic impact and legacy, and international legacy. Domestic legacy can be achieved at least in four dimensions. Firstly, there can be legal, institutional or organisational legacy. Legal and institutional status of various para-sports federations can be more streamlined, particularly as a result of the newly established Nippon Foundation Paralympic Support Centre. Secondly, there is an economic dimension which is mainly focused on the wider employment of disabled persons and stronger commitment of business sponsorship. Thirdly, one can envisage social legacy ranging from stronger promotion of accessibility for and wider social inclusion of disabled persons. Fourthly, one can add technological development both in instruments used by disabled persons and in the software to be used for facilitating communication with and among persons with disabilities. On the international dimension, one could count on the possible outcome of the “Sport For Tomorrow” initiative under which sports for the disabled in developing countries are expected to be promoted through economic cooperation.

Smith-Purcell (SP) radiations of weakly relativistic oversized backward wave oscillator (BWO) are examined experimentally. A bunching section composed of a coaxial slow wave structure with inner K-band corrugation is placed upstream from the oversized BWO. An annular beam less than 100 kV is self-bunched in the bunching section and then excites the oversized BWO. SP radiations are examined by using 25.5- and 45.0-GHz oversized BWOs. The beam is too far away from the walls of the oversized BWO for SP radiation to occur without the self-bunching. When the corrugation parameters of the bunching section are the same as those of the oversized BWO, enhanced SP radiations in the frequency region above the surface wave are observed even when the beam propagates outside the interaction region of the surface wave.

Beam interactions with surface waves and higher-order modes in an oversized backward wave oscillator (BWO) are studied. In addition to the well-known Cherenkov interaction, the slow cyclotron interaction occurs due to transverse perturbations of the electron beam. The Cherenkov interaction dominates the slow cyclotron interaction. Growth rates of both the interactions for the higher order modes are small compared with those for the surface-wave modes in an oversized BWO. The coaxial slow-wave structure exhibits a reduced number of higher-order modes, which consequently reduces the mode competition problem and improves beam interactions with higher-order modes. For higher values of beam currents, the slow cyclotron wave grows at a faster rate than the Cherenkov waves.

In this paper, the electromagnetic properties of a beam free trapezoidally corrugated slow wave structure (TCSWS) are numerically and experimentally investigated. The dimensions of the TCSWS are selected so that it can be deployed in $X$ -band backward wave oscillators (BWOs). The theoretical dispersion characteristics for the axisymmetric ${\rm TM}_{01}\hbox{--}{\rm TM}_{03}$ modes are obtained by solving the dispersion equation numerically. In order to verify the numerical calculation, a cold test is conducted using a 6-period TCSWS cavity and a vector network analyzer (VNA). The cavity is excited by a small needle-type antenna and frequency of the VNA is swept over the passbands. The dispersion characteristics are obtained from frequency values of the discrete resonant peaks of reflection measurement of each TM mode. Experimental results show an excellent agreement with numerical ones. The numerical and cold test results reveal that TCSWS can be used as an alternative to sinusoidally corrugated slow wave structure in BWO experiments with an advantage of ease of fabrication.

Electron beam generation in a weakly relativistic region of less than 100 kV is investigated utilizing rectangular and disk cold cathodes made of copper. Electron emission areas are located on the edges of the cathodes. For uniform electron emission, some surface roughness is required on the emission surface, which is obtained by scratching the surface with sandpaper. A uniform sheet beam with a size of about 2 × 40 mm and an annular beam with a diameter of about 25 mm and a thickness of about 2 mm are demonstrated in the weakly relativistic region. Stable electron beams of sheet and annular shapes are experimentally demonstrated.

Normal modes and slow-wave instabilities in an oversized coaxial slow-wave structure (SWS) are numerically analyzed for the case of a weakly relativistic annular beam. The coaxial SWS has outer and inner rectangular corrugations with K-band dimensions. The inner corrugations have a cylindrical surface wave, which is the fundamental mode and exists even if the outer conductor is removed. The outer corrugations generate higher-order waveguide modes. Both transverse and longitudinal beam perturbations are considered in the beam interactions, leading to slow cyclotron instabilities as well as Cherenkov instabilities. The instabilities of axisymmetric and nonaxisymmetric modes have almost the same growth rates. The relative position between the outer and inner corrugations affects the normal modes and may allow wide frequency tunability.

The temporal growth rate (TGR) in a trapezoidally corrugated slow-wave structure for a backward-wave oscillator is theoretically studied. An intense relativistic annular electron is used as the energy source for the device. The annular electron beam is assumed to be infinitesimally thin in the radial extent and guided by an infinitely strong magnetic field. The trapezoidal profile of the structure is approximated by a sinusoidal function using Fourier approximation, and the dispersion relation of the system is derived using the Rayleigh–Fourier method. To study the TGR of the electromagnetic wave inside the system, the dispersion equation is solved for different values of the beam parameters. The dimensions of sinusoidally corrugated comparable trapezoidal structure are determined by comparing their dispersion characteristics. For the ${\rm TM}_{01}$ mode, TGR of instability that gives a qualitative measure of the microwave generation is calculated. The peak TGR of the proposed structure is found to be on average 1.5% higher than that of the sinusoidally corrugated slow-wave structure for the same set of beam parameters. Apart from its improved growth rate, the proposed structure has an added advantage of easy fabrication.

Experimental studies of coaxial oversized backward wave oscillators (BWOs) are presented. The beam voltage is weakly relativistic, less than 100 kV. The slow-wave structure (SWS) consists of a rectangularly corrugated oversized hollow waveguide and rectangularly corrugated inner conductor and has a target operating frequency due to Cherenkov interaction is in the K-band. The coaxial SWS can have two surface waves caused by the inner and the outer corrugations. The oversized BWO operations under the influences of two surface waves are examined. The oscillation start voltage is decreased by introducing a rectangularly corrugated inner conductor. The output power is increased greatly as compared with those without the corrugated inner conductor. The inner corrugation improves the oversized BWO operation.

We experimentally studied an intense Smith-Purcell (SP) radiation based on a cylindrical corrugated waveguide driven by a weakly relativistic electron beam. The corrugated waveguide has a rectangular periodic structure, and an annular electron beam with energy less than 100 keV and current of the order of 100 A is injected. We observe both intense surface-wave radiation at 25 GHz and intense SP radiations up to 150 GHz. The observed SP radiations are enhanced by the sixth and fourth temporal harmonics of the surface wave. The characteristics of the enhanced SP radiation depend on the periodic number of the structure. In the experiment with the use of the 60-period structure, the observed power of the SP radiation at the fourth harmonic is higher than that of the radiation at the sixth harmonic. In the case of the 30 period-structure, the power level of the radiation at the sixth harmonic is comparable to that at the fourth harmonic.

It has been confirmed that the normal mode of a surface wave on a corrugated metal plate can be excited by a sheet electron beam. Two types of instabilities are analyzed numerically. One is the Cherenkov instability between the surface normal mode and the slow-space-charge mode of the electron beam. This instability is possibly absolute instability. The oscillation frequency of this instability can be controlled by the amplitude of the corrugation depth. The electron beam energy for this instability is determined by the ratio of the period length and the amplitude of the corrugation. Another is the Smith–Purcell-type instability. This instability is always convective-type instability. The oscillation frequency is higher than that of the above-mentioned Cherenkov instability and is in a broad band. The temporal growth rate of this instability is strongly reduced as the beam energy is reduced.

Generalized scaling laws for the formation of plasma confining potentials are investigated to find the physics essentials common to representative tandem-mirror operational modes in GAMMA 10. These modes are characterized in terms of (i) a high-potential mode and (ii) a hot-ion mode. The potential-formation scalings in these modes are consolidated and generalized on the basis of the consistency with finding of the wider validity of Cohen's strong electron-cyclotron heating (ECH) theory covering over both modes. A plateau-shaped electron distribution function is observed when a plug electron-confining potential is formed in the hot ion mode of GAMMA 10, as predicted in terms of the strong ECH theory.

(1) Four-time progress in ion-confining potentials Φ c to 3.0 kV in comparison to Φ c attained 1992-2002 is achieved in the hot-ion mode (T i =several keV). A scaling of Φ c , which favorably increases with plug electron-cyclotron heating (ECH) powers (P PECH ), is obtained. (2) The advance in Φ c leads to a finding of remarkable effects of radially sheared electric fields (dEr/dr) on turbulence suppression and transverse-loss reduction. (3) A weak decrease in Φ c with increasing n c to ∼10 19 m -3 with the recovery of Φ c with increasing P PECH is obtained. (4) The first achievement of active control and formation of an internal transport barrier (ITB) has been carried out with the improvement of transverse energy confinement. Off-axis ECH in an axisymmetric barrier mirror produces a cylindrical layer with energetic electrons, which flow through the central cell and into the end region. The layer, which produces a localized bumped ambipolar potential Φ c , generates a strong E r shear and peaked vorticity with the direction reversal of E r ×8 sheared flow near the Φ c peak. Intermittent vortex-like turbulent structures near the layer are suppressed in the central cell. This results in T e and T i rises surrounded by the layer. The phenomena are analogous to those in tokamaks with ITB. (5) Preliminary central ECH (170 kW, 20 ms) in a standard tandem-mirror operation raises T e0 from 70 to 300 eV together with T ι⊥0 from 4.5 to 6.1 keV, and T i//0 from 0.5 to 1.2 keV with τ P0 =95 ms for Φ c (=1.4 kV) trapped ions. The on-axis particle to energy confining ratio of τ P0 /τ E0 is observed to be 1.7 for Φ c trapped ions (consistent with Pastukhov's theory) and 2.4 for central mirror-trapped ions with 240-kW plug ECH and 90-kW ICH (η ICH ∼0.3; nl c =4.5×10 17 m -2 ). (6) Recently, a 200 kW central ECH with 430 kW plug ECH produces stable central-cell plasmas (T e =600 eV and T i =6.6 keV) with azimuthal E r ×B sheared flow. However, in the absence of the shear flow, hot plasmas migrate unstably towards vacuum wall with plasma degradation.

Macroprolactinemia was recognized more than a decade ago as a cause of hyperprolactinemia and the prevalence of macroprolactinemia is thought to be 10%-26% of patients with hyperprolactinemia. However, there are few published reports about macroprolactinemia in childhood. We report a 7-year-and-1-month-old girl with hyperprolactinemia due to macroprolactinemia with the complication of transient idiopathic central precocious puberty (ICPP). At the age of 6 years and 9 months, she was diagnosed with ICPP at another clinic, on the basis of isolated mammary development and increased height velocity with slightly advanced bone age. At that time, the unexpected finding of high PRL level was also observed. Four months later, she was referred to our clinic for persistently high PRL level. At this time, other endocrinological data showed prepubertal stage and we demonstrated macroprolactinemia and the presence of anti-PRL autoantibody. After other causes of hyperprolactinemia such as prolactinoma and stress were ruled out, we finally diagnosed her with hyperprolactinemia due to macroprolactinemia. Because most patients with macroprolactinemia are symptom-free despite hyperprolactinemia and drug therapy would not be indicated, macroprolactinemia should be suspected even in children to avoid unnecessary examinations and treatments.

Studies of an oversized BWO with a novel cathode and a rectangular corrugation are presented. The beam voltage is weakly relativistic, less than 100 kV. We propose to use a disk cathode made of metal only. The disk cathode can generate a uniformly distributed annular electron beam even in the weakly relativistic case. By using the annular electron beam, a weakly relativistic oversized BWO consisting of rectangularly corrugated cylindrical waveguide is demonstrated. The oscillation starting energy is about 60 kV for a 10-period rectangular corrugation. The maximum output power is estimated about 200 kW. The operation mode between axisymmetric and nonaxisymmetric modes can be controlled by changing the end condition of BWO.

Nonaxisymmetric Cherenkov and slow cyclotron instabilities in a backward wave oscillator are investigated by using a new version of self-consistent linear theory. The slow cyclotron instability as well as Cherenkov instability can be driven by an axial electron beam without any initial perpendicular velocity. In a low magnetic field region, the radial displacement of beam plays an important role in the beam interactions. The slow cyclotron instability becomes strong, when the perturbed cyclotron motion and the electromagnetic wave rotate in the same direction. The rotational direction of electromagnetic wave also affects the Cherenkov instability.

Performance of oversized backward wave oscillators (BWOs) is investigated. Due to the axial mode operation, there exists a critical value of beam energy for the oscillation, i.e., a starting energy. The output power depends on the beam radius and voltage. The maximum output powers are above 100 kW (K-band) and above 50 kW (Q-band). The corresponding quality factor Pf 2 is about 6×104 [kW·GHz2]. By changing the condition at the SWS end, an enhanced performance of the K-band oversized BWO is observed in a low magnetic field region about 0.4 T.

Operation mode of an oversized backward wave oscillator is studied experimentally, using an oversized slow-wave structure. The dispersion characteristics of the slow-wave structure are determined by the average radius, corrugation amplitude and pitch length of the periodic waveguide. The corrugation amplitude and the corrugation period mainly determine the upper cutoff frequency of the lowest mode. The lower cutoff frequency is determined by the average radius. In this work, a Q-band periodic slow-wave structure is fabricated from aluminum. The diameter of the slow-wave structure is about 4 times free space wavelength. The beam voltage is weakly relativistic, around 50 kV, and the beam current is in the range of 100 A. The output powers of several 10 kW are obtained in the Q-band, i.e., the estimated frequency is in the range of 34-41 GH. The output modes are examined by measuring the radiation patterns. Nonaxisymmetric as well as axisymmetric modes are observed. It is demonstrated for the first time that the nonaxisymmetric and axisymmetric operations of the oversized BWO can be controlled by changing the corrugation number of slow-wave structure.

We present atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying a radio frequency high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the formation of the plasma plume, the dependences of the plasma plume charge and the plasma plume length on the gas flow rate are examined. In a quartz tube with inner diameter 1.5 mm, which has more helium than air in the cross section of the flow channel, the distributions of the length and charge on the gas flow rate show similar tendencies. Consequently, when more helium gas is present than air, the travel length of the plasma plume correlates with the plasma plume charge. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Backward wave oscillators (BWOs) have a slow-wave structure (SWS) with periodically corrugated walls. To increase the operation frequency and the power handling capability, the SWS is oversized with the diameter larger than the free-space wavelength of output electromagnetic wave. Generally, the slow wave becomes a surface wave concentrated on the corrugation of oversized SWS. Excited surface waves are converted into radiating waves at the ends of SWS, leading to BWO radiations1. There exists an alternative mechanism to radiate electromagnetic waves in periodic structures, i.e., Smith-Purcell (SP) mechanism which directly excites radiating waves2. Original SP radiation was a spontaneous emission. SP radiation more intense than the original one was demonstrated based on the stimulated emission, in which self-bunching of electron beam due to the backward-wave interaction plays an essential role3.

Slow wave electron cyclotron maser composed of a periodically corrugated waveguide and an axially streaming electron beam is considered. This slow wave electron cyclotron maser can be driven by the...