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An application of electron-cyclotron heating with an off-axis resonance location produces a cylindrical layer with energetic electrons and facilitates the formation for a profile of plasma rotation...

The effects of the plasma-confining potentials and the associated radially sheared electric fields on the central-cell electron energy confinement are theoretically and experimentally investigated in the GAMMA 10 tandem mirror. In particular, the scaling of the central-cell electron temperatures with electron-confining potentials is studied on the basis of the local energy-balance equation. The obtained theoretical scaling of electron temperatures with electron-confining potentials is then compared with the experimentally observed relation between these two parameters. Recently, by the use of new 0.5-MW level gyrotrons in the plug region, four-time progress in the formation of the ion-confining potential Φ c including a new record of 3 kV has been achieved in a hot-ion mode having bulk-ion temperature T i = several keV. In the hot-ion mode, intermittent vortex-like turbulent structures are observed in the case without the gyrotron injections; in this case, radially produced weak shear ofelectric fields dE r /dr and appreciable transverse losses are observed. However, during the application of electron-cyclotron heatings, the associated potential rise produces a stronger shear in the central cell (dE r /dr = several 10 kV/m 2 ) resulting in the disappearance of such intermittent turbulent vortices with plasma confinement improvement. In order to investigate the effect of the radially sheared electric fields on the electron energy confinement, the radial profiles of the thermal diffusivity are derived from the local power-balance analysis by the use of the data from the following various diagnostics in the above-described hot-ion mode. The obtained radial profiles of radial electric field and thermal diffusivity imply that the reduction of the thermal diffusivity is associated with the radially produced strong shear of electric fields.

We improve the performance of the K-band oversized backward wave oscillator. The beam is annular and weakly relativistic. The beam voltage is less than 100 kV and the beam current is less than 500 ...

Interaction between an axially streaming electron beam and an axisymmetric TM mode in a periodically corrugated waveguide is analyzed using a linear fluid model. Effect of the perpendicular perturbation of the beam by a finite magnetic field is considered. There are two mechanisms of Cherenkov interaction between a beam and a TM mode. One is the conventional mechanism attributed to a longitudinal perturbation. The other is attributed to the vertical perturbation of the beam surface and is dominant in the low magnetic field region. The slow cyclotron mode on an axially streaming beam is able to interact with an axisymmetric TM mode only if beam surface modulation is taken into account. The Cherenkov and cyclotron interactions degenerate for zero magnetic fields. This interaction has higher growth rate compared to the conventional Cherenkov interaction in the region of high current and weakly relativistic energy.

Summary form given only. Recently, plasma techniques under atmospheric pressure circumstances have been adapted for industrial, medical and biological applications. Atmospheric pressure plasmas, such as a plasma jet are typically produced using an arc discharge and a dielectric barrier discharge (DBD). The arc discharge produces a high-temperature plasma, whereas DBD produces a low-temperature plasma, which results in less thermal damage to materials. Atmospheric pressure plasma of DBD is generated intermittently using dielectric, rate gas and metal electrode by applying radio frequency and high voltage1. When it is used a quartz tube as a dielectric, plasma is released to the atmosphere. A plasma plume is a small bulletlike volume of plasma traveling at unusually high velocities2. We have studied a generation of high density plasma jet using focused plasma jets3. However, the detailed properties of the plasma current and density were still not estimated. In this work, we use helium plasma jet produced using a quartz tube and copper foil electrodes where a low frequency (~13 kHz) and a high voltage (-6 ~ +9 kV) are applied. The measurement of plasma current is used by a current probe. The plasma drift velocity is measured indirectly by the drift velocity of luminous bullet on the time of flight method. The plasma cross-section is estimated on the photographs. The plasma density is evaluated from these measurements values. The dependences of plasma current and density on the helium gas flow rate are examined. Detail experimental results and discussion will be presented at the conference.

To clarify the growth pattern of body composition by body part for the management of childhood obesity, we measured body fat and muscle using BIA (bioelectrical impedance analysis) in 685 Japanese elementary schoolchildren (aged 6-11 years). The growth patterns of percentage body fat (%BF), fat mass (FM), and muscle mass (MM) were examined throughout the whole body and in various body parts. The %BF of the whole body was greater in females than in males, and this difference widened with age. The %BF, FM, and MM in each body part showed similar growth patterns and gender differences to those of the whole body. The mean %BF of the left limbs was higher than that of the right limbs at all age groups. BMI was strongly correlated with %BF in both sexes. In conclusion, the compositions of all body parts change similarly with age, and gender differences are also similar in childhood. The effect of one's dominant arm on body composition is seen at a young age. The accumulation of body composition data according to body part is indispensable for understanding childhood body composition and managing obesity.

Field patterns and Poynting vectors of TM 01 mode in sinusoidally corrugated waveguides are analyzed numerically.It is shown that a plasma column near the axis excludes the rf electric field lines towards the peripheral region, resulting in increased Poynting vectors in the axial direction there. The excitation of TM 01 mode in corrugated waveguides is shown to be classified into two cases; surface and the volume waves. A possible physical explanation for the enhanced radiation observed previously from plasma filled backward wave oscillators is tried from the present results.

The linear dispersion relation of low frequency electromagnetic plasma waves in a corrugated plasma waveguide is analyzed successfully for a particular model in which difficulties for satisfying Floquet theorem rigorously are overcome. The resultant absolute instabilities are investigated numerically in some detail.

An analytical method based on a new theoretical model for the x‐ray energy responses of silicon surface‐barrier (SSB) detectors has been proposed. This method may address a recent confusing issue in the x‐ray detection characteristics of SSB semiconductor detectors; that is, the x‐ray responses of SSB detectors as well as p‐i‐n diodes used in underbiased operations were recently found to be contrary to the commonly held belief that the x‐ray sensitivity of an SSB detector is determined by the thickness of the depletion layer. The model presented includes a signal contribution from thermally diffusing charge that is created in the field‐free substrate region within a diffusion length from the depletion layer along with a signal contribution from charge created in the depletion layer. This model predicts a large signal contribution from the charge‐diffusion effect on the SSB responses to high‐energy x rays. Formulas and calculated results supporting SSB calibration data have been represented. These analytic...

Numerical analysis for radiation level in a high-power backward wave oscillator with a finite-length slow-wave structure with end reflections has been made using an algorithm called the higher-order implicit difference method (HIDM). Spatial and temporal evolutions of a small localized disturbance in an RF field are followed by relativistic fluid equations and Maxwell equations. The radiation intensity of the oscillation decreases substantially with increasing energy spread beyond 10% of the beam.

Absolute instability in a plasma‐filled backward wave oscillator with sinusoidally corrugated slow wave structure driven by an intense relativistic electron beam has been analyzed numerically. The maximum spatial growth rate of the plasma‐filled waveguide is found to be larger than that of an optimally designed vacuum structure. The excitation of a finite length structure is investigated. Although the spatial growth rates obtained in the linear theory increase with plasma density in the finite length plasma‐filled structure for the fundamental TM01 mode of oscillation, negative global spatial growth rates prevent the coherent oscillation for intermediate ranges of plasma density, beam current, and even for structure length.

The linear theory of electromagnetic radiation from a localized plasma-loaded backward wave oscillator with sinusoidally corrugated slow wave structure driven by an annular intense relativistic electron beam has been derived and analyzed numerically. The enhanched radiation from a plasma-loaded structure is attributed to the increase in the spatial growth rate of the absolute instability. The backward wave oscillator instability without plasma is found to be most effective in a case where the beam travels near the wall of the slow wave structure. For the given number of plasma particles per unit length of the structure, the decrease in the plasma column radius enhances the output radiation.

An increase with time of the central-cell electron temperature during a period with thermal barrier potentials has been observed. The increase is explained by an improvement of the electron energy confinement due to the presence of thermal barriers. Different evolutions of the electron energy in the plug region have been observed; these are closely related with the variation in time of the confining potential of the plug electrons. The observed behaviour of the potential confined electrons provides the first data set for the evolution of the effect of thermal isolation caused by the formation of a thermal barrier in the kilovolt range.

A W-band (75 - 110 GHz) oversized surface wave oscillator driven by weakly relativistic electron beams with energy in the range of 10 - 80 keV is studied. Rectangular corrugations are used as slow-wave structures (SWS) having surface waves with an upper cutoff frequency of approximately 100 GHz (W-band). Uniformly distributed annular electron beams are generated by a disk-type cold cathode and then are injected into the W-band oscillator. A longer SWS length causes the oscillator to function in both backward wave oscillator (BWO) and travelling wave tube (TWT) operations, and no meaningful oscillation occurs at the π-point or the Bragg condition. When the SWS length is short enough, oscillation occurs in all regions: BWO, π-point and TWT. The operations of the oscillator are strongly affected by the structure length. The maximum radiation power is estimated to be approximately 20 kW with the figure of merit of about 2 × 102 MW.GHz2.

The linear theory of electromagnetic radiation from a backward-wave oscillator with a plasma-filled, sinusoidally corrugated waveguide driven by a relativistic electron beam has been derived and analyzed numerically. The presence of plasma can cause a substantial increase in the spatial growth rate of the absolute instability. For high plamsa densities, however, the absolute instability is suppressed and only the convective instability remains. The predicted radiation enhancement can be attributed to a decrease in the group velocity of the backward wave in the presence of a plasma.

A linear theory of the excitation of electromagnetic waves in a plasma-filled corrugated-wall waveguide with an arbitrarily large sinusoidal corrugation has been derived and analyzed numerically. The theory predicts that, when driven by an electron beam, the presence of a plasma in the slow wave structure will cause an increase in the oscillation frequency, and that the temporal growth rates of a high-frequency mode approach those of the fundamental mode for high plasma densities. The latter result may account for the high-frequency modes observed in the authors' plasma-filled backward-wave oscillator. >

A plateau-shaped electron distribution function is observed when an electrostatic electron-trapping potential is formed by the electron cyclotron heating (ECH) in the plug region of the GAMMA 10 tandem mirror. Also, a remarkable thermal isolation effect due to a kV-range thermal barrier is observed along with the difference between distribution functions in thermally separated regions. These new findings as well as the relation between ion-confining potentials and thermal-barrier potentials in the kV range consistently support the validity of Cohen's strong ECH theory.

An electric brake by a three-phase short-circuit system used as the brake equipment of a small wind turbine damages the rotor blades by a rapid revolution stopping of the generator. Moreover, the generators windings may also be damaged by a large short-circuit current. In this paper, the electric braking circuit using the NTC thermistors (negative temperature coefficient resistors) is proposed as a braking system for a cheaper and safe stop of the small wind turbine. The effect under the natural wind condition is examined by the field test using a 500W small wind turbine. AS a result, it is clarified that the generator can decelerates gradually and reduce the burst current by using the braking circuit that composed of the NTC thermisitors.

Aim: We analysed the body measurements of Japanese women to determine which factors may forecast adult obesity and also performed a comparative study of the utility of body mass index (BMI), which is used widely in Western Europe, and percentage of overweight, which is used in Japan. Methods: Subjects included 244 Japanese women who were born between 1983 and 1986. Using a questionnaire, we investigated anthropometric values from birth to present and parents’ present anthropometric data, and analysed factors that correlate with current BMI data. Results: (i) BMI after 10 years of age and BMI increase between ages 7 and 8 years correlated with BMI in adulthood. The carrying over rate of overweight increased with age. Meanwhile, percentage of overweight after 13 years onwards correlated with BMI in adulthood. (ii) Adult BMI positively correlated to both parents’ BMI. Conclusions: (i) For a Japanese woman, BMI in childhood is a good indicator of young adult BMI, and has the possibility of becoming an important parameter to monitor obesity progression. (ii) Therefore, attempts to control obesity in elementary school girls are necessary. (iii) Parents’ weights may potentially influence obesity in adulthood; however, further examination of other confounding factors is necessary.

We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and a foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. The helium gas flowing out of quartz tube mixes with air, and the flow channel is composed of the regions of flowing helium gas and air. The plasma plume length is equivalent to the reachable distance of flowing helium gas. Although the amount of helium gas on the flow channel increases by increasing the inner diameter of quartz tube at the same gas flow velocity, the plasma plume length peaks at around 8 m/s of gas flow velocity, which is the result that a flow of helium gas is balanced with the amount of gas. The plasma plume is formed at the boundary region where the flow of helium gas is kept to the wall of the air.

High-power microwave (HPM) sources based on electron cyclotron resonance (ECR) such as gyrotrons are fast wave devices and velocity component of electron beam perpendicular to guiding magnetic field is the origin of HPM. HPM sources based on Cherenkove mechanism are slow wave devices and can be driven by a beam without initial perpendicular velocity. The authors present here the experimental result that seems to be the first demonstration of high-power slow wave electron cyclotron maser (ECM) consisting of a large diameter sinusoidally corrugated metal waveguide driven by a beam with predominant parallel velocity. The designed size parameters of slow wave structure (SWS) are as follows: average radius 30 mm, corrugation pitch 3.4 mm, its amplitude h = 1.7 mm and total length 238 mm. They use an annular beam with radius 26.3 mm, energy 55 keV, current 200 A in their experiment. Expected Cherenkov oscillation frequency of TM01 mode is 20 GHz. The observed high-power microwaves can be quantitatively explained by a backward wave oscillation with Cherenkov mechanism enhanced by positive feedback of anomalous Doppler slow cyclotron wave. In conclusion, the slow wave ECM presented here will be a competitive candidate against gyrotrons for generating multi-MW millimeter microwaves available inmore » fusion plasma research.« less

Summary form only given, as follows. We study beam instabilities by developing a new version of self-consistent, linear theory considering three dimensional beam perturbations.

Summary form only given, as follows. Operation modes of oversized backward wave oscillators are studied experimentally Two kinds of periodic slow wave structures (SWSs) are fabricated.

We studied a G-band oversized backward wave oscillator (BWO) driven by a weakly relativistic electron beam of less than 100 kV. Rectangular corrugations are used as slow-wave structures having surface waves with upper cutoff frequencies above 150 GHz (G-band). We examine how dispersion characteristics of surface waves are affected by accuracy in machining the corrugation amplitude, width, and period length. Of these, accuracy in the amplitude has the largest effect. Uniformly distributed annular electron beams are generated by a disk-type cold cathode and injected into the G-band BWO. G-band BWO operations in 137 - 173 GHz and above 173 GHz are achieved by changing the corrugation amplitude. The radiation patterns are fairly broad, and the estimated radiation power is at kW level.

We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the properties of the plasma plume, the plasma plume current is estimated from the difference in currents on the circuit, and the drift velocity is measured using a photodetector. The relation of the plasma plume density n plu, which is estimated from the current and the drift velocity, and the gas flow velocity v gas is examined. It is found that the dependence of the density on the gas flow velocity has relations of n plu ∝ log(v gas). However, the plasma plume density in the laminar flow is higher than that in the turbulent flow. Consequently, in the laminar flow, the density increases with increasing the gas flow velocity.

Surface waves in oversized G-band slow-wave structure with rectangularly corrugated wall are analyzed numerically. The inner corrugation generates cylindrical surface wave. The outer corrugation also generates transverse magnetic surface wave. The upper cut-offs of surface waves are controlled by corrugation amplitude. In excitation of the surface waves by an annular electron beam, the slow cyclotron interaction as well as the Cherenkov interaction occur due to there-dimensional beam perturbations. The slow cyclotron interaction merges with the Cherenkov interaction at lower magnetic field. The merged growth rate is enhanced by 13 % as compared to the isolated Cherenkov growth rate. The surface waves on inner and outer corrugations can have different frequencies and can be excited selectively by adjusting the beam radius of the electron beam.

Higher order mode radiations of oversized K-band backward wave oscillator (BWO) are examined experimentally. By injecting an annular beam in the weakly relativistic region less than 100 kV, a beam mode with harmonic number n = 1 excites BWO radiations based on the TM01 surface wave. The same beam mode excites higher order modes leading to radiations in the U- and E-bands. The power levels of the higher order modes are hundreds of times smaller than that of BWO due to the surface wave. For a beam mode with n = 2, higher order mode radiations are in the F- and D-bands, up to about 100 GHz, which is about four times higher than the frequency of the TM01 surface wave. The power level of higher order mode radiation by the n = 2 beam mode decreases by a factor of hundreds from that of the n = 1 beam mode.

Summary form only given, as follows. Recent experiments with the plasma-loaded, 8.5 GHz, relativistic backward wave oscillator (BWO) showed an increase in the microwave interaction efficiency up to 40% and the possibility of operation at beam currents beyond the vacuum limit. Our goal is to analyze and optimize interaction between the electron beam and electromagnetic fields in plasma-loaded periodic slow wave structures filled with plasma. In this work, we measured electromagnetic dispersion characteristic of a plasma-loaded corrugated slow wave structure. A hydrogen flashover gun generated a plasma column which was guided by a magnetic field (2-15 kG) and filled a periodic slow wave structure. Since the structure is of finite length, resonances occur only for discrete values of the wavenumbers. Introduction of plasma into the slow wave structure was expected to cause upward frequency shifts of the resonances. The frequency upshifts associated with the TM/sub 01/ mode in the periodic slow wave structure were measured as a function of the background plasma density by a single port (S/sub 11/) method. In order to determine the background plasma density the same technique was used for a smooth wall cavity. We measured frequency shifts on the order of 0.1 GHz around a center frequency of 8.5 GHz for the plasma density of about 10/sup 11/ cm/sup -3/. The obtained resonance frequency upshifts in the plasma-loaded slow wave structure showed good agreement with theoretical calculations.

We present a numerical and experimental study of the dispersion characteristics of cylindrical surface waves on metallic cylinders with rectangular corrugations. In actual devices, reflections at both ends quantize the electromagnetic modes into resonant axial modes. A cavity method based on axial mode measurements is applied to study the properties of the cylindrical surface waves. The resonances are relatively sharp near the upper cutoff, but at low frequencies far from the cutoff, the resonances broaden to resemble those of a Sommerfeld wave. c

Backward wave oscillation based on a cylindrical surface wave of Smith-Purcell free electron laser (SP-FEL) is demonstrated. The SP-FEL is composed of a metal cylinder having a periodically corrugated wall and a surrounding hollow straight waveguide. Corrugation parameters are those used in K-band backward wave oscillators (BWOs). The metal cylinder has a surface wave due to the corrugation. The cylindrical surface wave is excited by an axially injected coaxial annular beam. Radiations due to the backward wave oscillation based on the cylindrical surface wave are examined in a weakly relativistic region less than 100 kV. An oscillation starting voltage exists for the backward wave oscillation as in the case of hollow oversized BWO. The frequencies are in K-band and are determined by the cylindrical corrugation. Radiations up to tens of kW are obtained.

Summary form only given. Cold tests have been performed on a slow-wave structure made from a cylindrical waveguide with sinusoidally varying radius. To study the dispersion relation, a cavity was formed by shorting a section of the structure between metal plates placed at planes of mirror symmetry. A simple axial wire antenna was used to launch azimuthally symmetric TM (transverse magnetic) modes. The end reflection was measured on the 8-period beam test structure to include the effect of the output taper. Since the input side was cutoff to all TM modes, one only needed to measure reflection for the output side of the structure. This reflection was found by measuring the diffractive quality factor of the structure.

Three kinds of models are used for beam instability analyses: those based on a solid beam, an infinitesimally thin annular beam, and a finitely thick annular beam. In high-power experiments, the electron beam is an annulus of finite thickness. In this paper, a numerical code for a sinusoidally corrugated waveguide with a finitely thick annular beam is presented and compared with other models. Our analysis is based on a new version of the self-consistent linear theory that takes into account three-dimensional beam perturbations. Slow-wave instabilities in a K-band oversized sinusoidally corrugated waveguide are analyzed. The dependence of the Cherenkov and slow cyclotron instabilities on the annular thickness and guiding magnetic field are examined.

The dispersion characteristics and slow-wave instabilities of a sinusoidally corrugated waveguide with coaxial slow-wave structure (SWS) are analyzed. In SWS, a central cylindrical conductor is surrounded by an outer cylindrical conductor. Sinusoidal corrugation is formed on either conductor or both conductors. The corrugation parameters are those used for an X-band SWS. The relative phase between the sinusoidal corrugations on the inner and outer conductors affects the dispersion characteristics. Instabilities due to beam interactions with the slow -waves are examined by considering three-dimensional beam perturbations. The slow cyclotron instability occurs in addition to the Cherenkov instability, since transverse as well as longitudinal perturbations are included.

Studies of coaxial oversized backward wave oscillators (BWOs) are reported. The beam voltage is weakly relativistic (less than 100 kV). The slow-wave structure consists of a periodically corrugated oversized waveguide and periodically corrugated inner conductor, whose target operating frequency due to Cherenkov interaction is in the K-band. A starting energy exists for the coaxial oversized BWO as it does for a hollow oversized BWO. The coaxial slow-wave structure has two surface wave modes caused by the inner and outer corrugations. Operation based on these surface modes can be controlled by the beam diameter. The phase difference between the inner and outer corrugations has little effect on operation of the oversized BWO.

Studies of slow cyclotron maser operation of a slow-wave device are presented. The beam voltage is weakly relativistic, less than 100 kV. The slow-wave structure is a periodically corrugated oversized waveguide for Kband operation. When using rectangular corrugation having a relatively small ratio of corrugation width to periodic length of about 20 %, the dispersion curve near the upper cut-off becomes flat and second harmonic slow cyclotron maser operation is observed in the low-energy region near 30 kV. Another type of combined resonance of Cherenkov and slow cyclotron interaction is also demonstrated in which an absolute instability is driven by the slow cyclotron interaction. By using sinusoidal corrugation and rectangular corrugation having a 50 % ratio of corrugation width to periodic length, amplification effects due to the fundamental and second harmonic slow cyclotron interactions are observed.

Studies on slow-wave devices with a novel disk cathode and two types of rectangular corrugation are reported. The beam voltage is weakly relativistic, which is less than 100 kV. A disk cathode can generate a uniformly distributed annular beam in the weakly relative region. Rectangular corrugation having the ratio of the corrugation width to the periodic length of 50 or 20% is used. Using the former, output powers of about 200 kW are obtained at around 100 kV. For the latter, the effect of slow cyclotron resonance is observed in the low-energy region of around 30 kV. Output powers of slow cyclotron masers are in the range of a few hundred W. The operation mode of a slow cyclotron maser can be controlled between axisymmetric and nonaxisymmetric modes by changing the end condition of rectangular corrugation.

The cherenkov and slow cyclotron instabilities driven by an axially injected electron beam in a cylindrical waveguide are studied using a new version of the self-consistent linear theory considering three-dimensional beam perturbations. There are three kinds of models for beam instability analysis, which are based on a cylindrical solid beam, an infinitesimally thin annular beam, and a finitely thick annular beam. Among these models, the beam shape properly representing the often used actual annular electron beams is the finitely thick annulus. We develop a numerical code for a cylindrical waveguide with a finitely thick annular beam. Our theory is valid for any beam velocity. We present eigen-modes of the cylindrical system with the plasma and beam. Instabilities driven by the annular beam in a dielectric-loaded waveguide are also examined.

Summary form only given. A linear theory of electromagnetic radiation from a high-power backward wave oscillator (BWO) with a plasma filled, sinusoidally corrugated waveguide driven by a relativistic electron beam has been derived and analyzed numerically. It was shown that the experimental results of Minami et al. (1988) and Carmel et al. (1989) on enhanced radiation from plasma BWOs can be explained by the linear theory developed. It is concluded that the present analysis of the absolute instability makes possible the practical design of high-power, coherent, and enhanced plasma BWOs

The dispersion relation of a rectangularly periodic cylindrical slow-wave structure (SWS) with an annular electron beam of energy

We report an oversized K-band backward wave oscillator (BWO) operating above 20 GHz in the weakly relativistic region less than 100 kV. It is very important to prevent microwave from going into the beam diode, since intense microwaves will harmfully affect beam generation. A weakly relativistic oversized BWO is demonstrated using a Bragg reflector at the beam entrance of slow wave structure (SWS). The effect of the Bragg reflector on the BWO operation is examined, by changing the boundary condition at the beam entrance. The Bragg reflector improves the performance of the oversized BWO.

The Cherenkov instability used in slow-wave devices has been well studied in the literature. However, in previous analyses, the beam motion is restricted to the longitudinal direction assuming an infinitely strong magnetic field. For the finite strength magnetic field, the transverse beam perturbation cannot be ignored and leads to the slow cyclotron instability. Recently, a new version of self-consistent, field theory considering three-dimensional perturbation has been developed based on a solid beam. in which the effect of the transverse perturbation appears as a surface charge at a fixed boundary. In the case of a thin annular beam. the boundary is modulated and is essentially different from the solid beam case. We propose a self-consistent field theory considering the moving modified boundary surface. The slow cyclotron instability due to the modulation of an infinitesimally thin annular electron beam is presented.

Backward wave oscillators (BWOs) have been studied as a candidate hiph-power microwave source. To increase the operation frequency, an oversized slow-wave structure (SWS) is used. The operation at reduced voltage is preferable for practical applications. This work is aimed at numerically examining the operation mode of a weakly relativistic oversized BWO. We examine not only the axisymmetric transverse magnetic mode but also the non-axisymmetric hybrid modes of the oversized SWS. Both of them are candidates for the operation modes. These modes are surface waves whose fields are concentrated near the SWS wall. They overlap in frequency and are not separated by stop-hands. For an efficient beam interaction, the injected electron beam needs to be controlled more accurately than in the non-oversized SWS case.

For the purpose of end-loss-ion and -electron analyses in open-field plasmas, a compact-sized electrostatic end-loss-current detector is proposed on the basis of a self-collection principle for suppressing the effects of secondary-electron emission from a metal collector. For employing this specific method, it is worth noting that no further additional magnetic systems except the ambient open-ended magnetic fields are required in the detector operation. This characteristic property provides a compactness of the total detection system and availability for its use in plasma confinement devices without disturbing plasma-confining magnetic fields. The detector consists of a set of parallel metal plates with respect to lines of ambient magnetic forces of a plasma device for analyzing incident ion currents along with a grid for shielding the collector against strays due to the metal-plate biasing. The characterization experiments are carried out by the use of a test-ion-beam line along with an additional use of a Helmholtz coil system for the formation of open magnetic fields similar to those in the GAMMA 10 end region. The applications of the developed end-loss-current detector in the GAMMA 10 plasma experiments are demonstrated under the conditions with simultaneous incidence of energetic electrons produced by electron-cyclotron heatings for end-loss-plugging potential formation.

Our proposed “matrix-type” semiconductor detectors are applied for studying the local energy balance of bulk electrons in the tandem-mirror GAMMA 10. The matrix-type detector array consists of compactly produced six “rows” having different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channel units (“columns”) for measuring radiation profiles in the radial direction of plasmas. These various SiO2 layers are, thus, employed as “unbreakable ultrathin radiation-absorption filters” having various thicknesses to distinguish x rays from charge-exchange neutral particles and analyze the radial profiles of both plasma ion and electron temperatures simultaneously. The radial profiles of the energy confinement time and the thermal diffusivity obtained from the local energy balance analysis imply that the improvement of the plasma confinement is associated with the strong shear of radial electric fields due to a high plasma confining potentials.

The quantum efficiency of an ultralow-energy-sensitive pure-Ge (ULE Ge) detector is investigated using synchrotron radiation from the storage ring at AIST especially for x-ray pulse-height analyses (PHAs), down to a few hundred eV. Several types of x-ray diagnostics such as x-ray PHA, x-ray absorption methods, and x-ray tomography using the ULE Ge detector, a NaI(Tl) detector, as well as a microchannel-plate tomography system are employed for investigating electron distribution functions and electron temperature profiles with preliminary central electron-cyclotron heating in the central cell of the GAMMA 10 tandem mirror. These measurements play an important role in studying an essential physics scaling of the electron temperature as a function of electron confining potential in tandem mirror plasmas.