Publisher：ICEAST 2018 - 4th International Conference on Engineering, Applied Sciences and Technology: Exploring Innovative Solutions for Smart Society  

We developed a prototype radar for sea-tide level measurement. The radar was evaluated in a laboratory room. It was confirmed that the radar could detect the change in the position of a target with a resolution of <1 mm. We also evaluated the phase-detection performance of scattered waves in an anechoic chamber and confirmed that the phase profiles measured at vertically different antenna positions agree well with theoretical calculations.

DOI： 10.1109/ICEAST.2018.8434449

Scopus

Publisher：IMBioc 2018 - 2018 IEEE/MTT-S International Microwave Biomedical Conference  

This paper presents noncontact measurement of vital signals using microwave reflectometry. Elimination of the spurious component due to random movement of human subject has been the biggest problem for microwave measurement. Auto-gain control of the receiver, template matching and cross-correlation technique among multiple reflectometers enable motion artifact elimination, signal peak detection, and data processing for various parameters. We focus here on the real-time measurements of heart rate (HR) and heart rate variability (HRV). Those measurements are performed by both reflectometer and conventional electrocardiograph (ECG) for each other comparison. The evaluation of HR and HRV using microwave reflectometry is completely noninvasive and feasible even through clothing, which is extremely effective to daily life and driver's monitoring.

DOI： 10.1109/IMBIOC.2018.8428948

Scopus

Publisher：Advances in Physics: X  

Progress in microwave and millimeter-wave technologies has made possible advanced diagnostics for application to various fields, including radio astronomy, alien substance detection, plasma diagnostics, airborne and space-borne imaging radars called as synthetic aperture radars, and living body measurements. Transmission, reflection, scattering, and radiation processes of electromagnetic waves are utilized as diagnostic principles. The diagnostics are classified as active and passive systems. Specifically, active radar reflectometry has become of importance in various applications due to the possibility of high localization and accessibility of the measurements as well as the non-invasive nature of the systems. In this paper, recent development and application of radar reflectometers are described. The key words are profile reflectometry, fluctuation reflectometry, imaging radar (optics imaging and synthetic aperture imaging), and radio-optics fusion technology in order to improve the spatial resolution.

DOI： 10.1080/23746149.2018.1472529

Scopus

Publisher：Journal of Instrumentation  

Turbulence measurement is important in the study of plasma confinement. We developed a multi-channel correlation electron cyclotron emission (cECE) radiometer system, using an existing conventional ECE radiometer system (RADH) on a large helical device (LHD). The signal received by the RADH was split and fed to our cECE system, and then electron temperatures at three separate radial positions were measured by resolving frequency component with three narrow (200 MHz) band-pass filters. Data taken by the cECE system were compared with those taken by the RADH system. Turbulence-like signals below 10 kHz were detected by the cECE measurement using coherence analysis, but were not detected by RADH measurement. We considered this to be due to differences in the radial separation length between the two channels and in the radial measurement depth of each channel. The cECE system was able to detect higher frequency turbulence because its separation length and measurement depth in the radial direction was shorter than the correlation length of the turbulence.

DOI： 10.1088/1748-0221/11/01/C01072

Scopus

Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

In this paper, we present an ultra-wideband microwave-modulated laser radar which is designed and fabricated for improvement of the spatial resolution both in the range direction and the azimuth direction. The amplitude modulation in a range of 0.01-18 GHz is applied to an infrared laser source of 1550 nm wavelength. The frequency and the bandwidth are assigned by the Administration of Radio under the Ministry of Internal Affairs and Communications in Japan. However, there is no bandwidth limitation in the infrared region. Considering the influence of radiation pattern for microwave antennas case, there is no side lobe in laser beam transmission. Ambiguous signal and interferences which are returned from the ground can be suppressed. A prototype of laser-radar system with a fiber collimator for both transmitting and receiving optics has been fabricated. A vector network analyzer is used to obtain S21 signal between the microwave modulation input and that of received signal. The system is, at first, applied to the measurement of the distance (position) of an object. It is proved that the spatial resolution is less than 1 cm during 5-10 m. As an initial experiment, we have succeeded to obtain 3D image of object by scanning a laser beam in two dimensions.

DOI： 10.1117/12.2236326

Scopus

Publisher：Journal of Instrumentation  

Microwave imaging diagnostics are powerful tools that are used to obtain details of complex structures and behaviors of such systems as magnetically confined plasmas. For example, microwave imaging reflectometry and microwave imaging interferometers are suitable for observing phenomena that are involved with electron density fluctuations; moreover, electron cyclotron emission imaging diagnostics enable us to accomplish the significant task of observing MHD instabilities in large tokamaks. However, microwave imaging systems include difficulties in terms of multi-channelization and cost. Recently, we solved these problems by developing a Horn-antenna Mixer Array (HMA), a 50 - 110 GHz 1-D heterodyne- type antenna array, which can be easily stacked as a 2-D receiving array, because it uses an end-fire element. However, the HMA still evidenced problems owing to the requirement for local oscillation (LO) optics and an expensive high-power LO source. To solve this problem, we have developed an upgraded HMA, named the Local Integrated Antenna array (LIA), in which each channel has an internal LO supply using a frequency multiplier integrated circuit. Therefore, the proposed antenna array eliminates the need for both the LO optics and the high-power LO source. This paper describes the principle of the LIA, and provides details about an 8 channel prototype LIA.

DOI： 10.1088/1748-0221/10/12/C12031

Scopus

Publisher：Plasma and Fusion Research  

Microwave to millimeter-wave diagnostics techniques, such as interferometry, reflectometry, scattering, and radiometry, have been powerful tools for diagnosing magnetically confined plasmas. The resultant measurements have clarified several physics issues, including instability, wave phenomena, and fluctuation-induced transport. Electron cyclotron emission imaging has been an important tool in the investigation of temperature fluctuations, while reflectometry has been employed to measure plasma density profiles and their fluctuations. We have developed a horn-antenna mixer array (HMA), a 50 - 110 GHz 1D antenna array, which can be easily stacked as a 2D array. This article describes an upgrade to the horn mixer array that combines well-characterized mixers, waveguide-to-microstrip line transitions, intermediate frequency amplifiers, and internal local oscillator modules using a monolithic microwave integrated circuit technology to improve system performance. We also report on the use of a multi-channel HMA system.

DOI： 10.1585/pfr.10.3402034

Scopus

Publisher：Review of Scientific Instruments  

We propose a new interferometer system for density profile measurements. This system produces multiple measurement chords by a leaky-wave antenna driven by multiple frequency inputs. The proposed system was validated in laboratory evaluation experiments. We confirmed that the interferometer generates a clear image of a Teflon plate as well as the phase shift corresponding to the plate thickness. In another experiment, we confirmed that quasi-optical mirrors can produce multiple measurement chords; however, the finite spot size of the probe beam degrades the sharpness of the resulting image.

DOI： 10.1063/1.4893430

Scopus

Publisher：Review of Scientific Instruments  

A new antenna array is proposed in order to improve the sensitivity and complexity of microwave imaging diagnostics systems such as a microwave imaging reflectometry, a microwave imaging interferometer, and an electron cyclotron emission imaging. The antenna array consists of five elements: a horn antenna, a waveguide-to-microstrip line transition, a mixer, a local oscillation (LO) module, and an intermediate frequency amplifier. By using an LO module, the LO optics can be removed, and the supplied LO power to each element can be equalized. We report details of the antenna array and characteristics of a prototype antenna array. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4885471

Scopus

Publisher：Physics of Plasmas  

We report the observation of electromagnetic radiation at high harmonics of the electron cyclotron frequency that was considered to be converted from electrostatic waves called electron Bernstein waves (EBWs) during magnetic reconnection in laboratory overdense plasmas. The excitation of EBWs was attributed to the thermalization of electrons accelerated by the reconnection electric field around the X-point. The radiative process discussed here is an acceptable explanation for observed radio waves pulsation associated with major flares.

DOI： 10.1063/1.4900872

Scopus

Publisher：Journal of Electromagnetic Waves and Applications  

Ultra-wideband microwave-modulated laser radar is designed and fabricated for the improvement of spatial resolution both in the range and in the azimuth directions. The frequency modulation (1-18 GHz chirp) is applied to an infrared laser source in 1550 nm wavelength. A prototype of laser radar system with a beam expander has been constructed and applied to the measurement of the distance (position) of an object. In the experiment, it has been proved that the spatial resolution in the range direction is less than ±2 cm. © 2014 Taylor & Francis.

DOI： 10.1080/09205071.2014.917994

Scopus

Publisher：Conference Proceedings of 2013 Asia-Pacific Conference on Synthetic Aperture Radar, APSAR 2013  

We have developed spotlight mode SAR called Live SAR for flood area surveillance. Live SAR has many feature for flexible measurement. The radar system is enough light to mount on small plane, and is able to take an image of various area with an antenna on a gimbal. Live SAR can control by an easy user interface software, and can automatically outputs very high-resolution image (0.1 m) within few tens of seconds. Live SAR has been tested both on ground and helicopter in Fukuoka and Utsunomiya area which include river and sea water, and could successfully generate high resolution image. It is confirmed that the water area looks dark due to a low radar cross section. We could take some such an image to estimate the water area and water volume. As well as fixed target image, moving target has been also detected. This feature will become very important to detect the water flow direction and people refuge. © 2013 IEICE.

Scopus

Publisher：Nuclear Fusion  

Since the first H-mode discharges in 2010, the duration of the H-mode state has been extended and a significantly wider operational window of plasma parameters has been attained. Using a second neutral beam (NB) source and improved tuning of equilibrium configuration with real-time plasma control, a stored energy of Wtot ∼ 450 kJ has been achieved with a corresponding energy confinement time of τE ∼ 163 ms. Recent discharges, produced in the fall of 2012, have reached plasma βN up to 2.9 and surpassed the n = 1 ideal no-wall stability limit computed for H-mode pressure profiles, which is one of the key threshold parameters defining advanced tokamak operation. Typical H-mode discharges were operated with a plasma current of 600 kA at a toroidal magnetic field BT = 2 T. L-H transitions were obtained with 0.8-3.0 MW of NB injection power in both single- and double-null configurations, with H-mode durations up to ∼15 s at 600 kA of plasma current. The measured power threshold as a function of line-averaged density showed a roll-over with a minimum value of ∼0.8 MW at . Several edge-localized mode (ELM) control techniques during H-mode were examined with successful results including resonant magnetic perturbation, supersonic molecular beam injection (SMBI), vertical jogging and electron cyclotron current drive injection into the pedestal region. We observed various ELM responses, i.e. suppression or mitigation, depending on the relative phase of in-vessel control coil currents. In particular, with the 90° phase of the n = 1 RMP as the most resonant configuration, a complete suppression of type-I ELMs was demonstrated. In addition, fast vertical jogging of the plasma column was also observed to be effective in ELM pace-making. SMBI-mitigated ELMs, a state of mitigated ELMs, were sustained for a few tens of ELM periods. A simple cellular automata ('sand-pile') model predicted that shallow deposition near the pedestal foot induced small-sized high-frequency ELMs, leading to the mitigation of large ELMs. In addition to the ELM control experiments, various physics topics were explored focusing on ITER-relevant physics issues such as the alteration of toroidal rotation caused by both electron cyclotron resonance heating (ECRH) and externally applied 3D fields, and the observed rotation drop by ECRH in NB-heated plasmas was investigated in terms of either a reversal of the turbulence-driven residual stress due to the transition of ion temperature gradient to trapped electron mode turbulence or neoclassical toroidal viscosity (NTV) torque by the internal kink mode. The suppression of runaway electrons using massive gas injection of deuterium showed that runaway electrons were avoided only below 3 T in KSTAR. Operation in 2013 is expected to routinely exceed the n = 1 ideal MHD no-wall stability boundary in the long-pulse H-mode (10 s) by applying real-time shaping control, enabling n = 1 resistive wall mode active control studies. In addition, intensive works for ELM mitigation, ELM dynamics, toroidal rotation changes by both ECRH and NTV variations, have begun in the present campaign, and will be investigated in more detail with profile measurements of different physical quantities by techniques such as electron cyclotron emission imaging, charge exchange spectroscopy, Thomson scattering and beam emission spectroscopy diagnostics. © 2013 IAEA, Vienna.

DOI： 10.1088/0029-5515/53/10/104005

Scopus

Publisher：2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings  

Progress in micro- to millimeter-wave technologies have made possible advanced diagnostics (imaging) for various applications, such as, plasma diagnostics, radio astronomy, alien substance detection, airborne and spaceborne imaging radars called as synthetic aperture radars, living body measurements. In this report we focus on the reflectometric (radar) techniques applied to plasma diagnostics and biomedical measurement. © 2013 IEICE.

Scopus

Publisher：Fusion Science and Technology  

We proposed a flexible electron density measurement system based on the interferometer for confinement study. An INRD guide antenna for spatial scan capability of a probe beam has been analytically designed. As a result of fabricating and evaluating the antenna, it was confirmed that the antenna has a predicted performance. We also evaluated the analysis method of a sampled data with numerical simulation in order to calculate phase shift due to the plasma density. A 3000 order FIR filter could successfully separate a sample signal with various frequencies into a signal with a single frequency when S/N is not critical.

DOI： 10.13182/FST13-1T17

Scopus

Publisher：Review of Scientific Instruments  

We propose a new interferometer concept that can realize electron-density distribution measurement with high spatial and moderate temporal resolution. The image non-radiative dielectric guide antenna can probe a wide measurement area simultaneously. We fabricated the antenna with an electromagnetic simulator and confirmed that the simulated and measured radiation patterns are consistent with each other. In addition, we found that the antenna shows the required characteristics such as scanning characteristics, which depend on the input frequency. © 2012 American Institute of Physics.

DOI： 10.1063/1.4734488

Scopus

Publisher：Review of Scientific Instruments  

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO. © 2012 American Institute of Physics.

DOI： 10.1063/1.4729259

Scopus

Publisher：Journal of Instrumentation  

Progress in microwave and millimeter-wave technologies has made possible advanced diagnostics for application to various fields, such as, plasma diagnostics, radio astronomy, alien substance detection, airborne and spaceborne imaging radars called as synthetic aperture radars, living body measurements. Transmission, reflection, scattering, and radiation processes of electromagnetic waves are utilized as diagnostic tools. In this report we focus on the reflectometric measurements and applications to biological signals (vital signal detection and breast cancer detection) as well as plasma diagnostics, specifically by use of imaging technique and ultra-wideband radar technique. © 2012 IOP Publishing Ltd and SISSA.

DOI： 10.1088/1748-0221/7/01/C01089

Scopus

Publisher：Plasma and Fusion Research  

Techniques for visualizing turbulent flow in nature and in the laboratory have evolved over half a millennium from Leonardo da Vinci's sketches of cascading waterfalls to the advanced imaging technologies which are now pervasive in our daily lives. Advancements in millimeter wave imaging have served to usher in a new era in plasma diagnostics, characterized by ever improving 2D, and even 3D, images of complex phenomena intokamak and stellarator plasmas. Examples at the forefront of this revolution are electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry (MIR). ECEI has proved to be a powerful tool as it has provided immediate physics results following successful diagnostic installations on TEXTOR, ASDEX-U, DIIID, and KSTAR. Recent results from the MIR system on LHD are demonstrating that this technique has the potential for comparable impact in the diagnosis of electron density fluctuations. This has motivated a recent resurgence in MIR research and development, building on a prototype system demonstrated on TEXTOR, toward the realization of combined ECEI/MIR systems on DIII-D and KSTAR for simultaneous imaging of electron temperature and density fluctuations. The systems discussed raise the standard for fusion plasma diagnostics and present a powerful new capability for the validation of theoretical models and numerical simulations. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

DOI： 10.1585/pfr.6.2106042

Scopus

Publisher：Nuclear Fusion  

Since the successful first plasma generation in the middle of 2008, three experimental campaigns were successfully made for the KSTAR device, accompanied with a necessary upgrade in the power supply, heating, wall-conditioning and diagnostic systems. KSTAR was operated with the toroidal magnetic field up to 3.6 T and the circular and shaped plasmas with current up to 700 kA and pulse length of 7 s, have been achieved with limited capacity of PF magnet power supplies. The mission of the KSTAR experimental program is to achieve steady-state operations with high performance plasmas relevant to ITER and future reactors. The first phase (2008-2012) of operation of KSTAR is dedicated to the development of operational capabilities for a super-conducting device with relatively short pulse. Development of start-up scenario for a super-conducting tokamak and the understanding of magnetic field errors on start-up are one of the important issues to be resolved. Some specific operation techniques for a super-conducting device are also developed and tested. The second harmonic pre-ionization with 84 and 110 GHz gyrotrons is an example. Various parameters have been scanned to optimize the pre-ionization. Another example is the ICRF wall conditioning (ICWC), which was routinely applied during the shot to shot interval. The plasma operation window has been extended in terms of plasma beta and stability boundary. The achievement of high confinement mode was made in the last campaign with the first neutral beam injector and good wall conditioning. Plasma control has been applied in shape and position control and now a preliminary kinetic control scheme is being applied including plasma current and density. Advanced control schemes will be developed and tested in future operations including active profiles, heating and current drives and control coil-driven magnetic perturbation. © 2011 IAEA, Vienna.

DOI： 10.1088/0029-5515/51/9/094006

Scopus

Language：Japanese  

Language：English  

Publisher：Plasma and Fusion Research  

A broadband heterodyne radiometer system has been developed and installed on KSTAR to measure second harmonic electron cyclotron emission (ECE) at the magnetic field of 3 T. The system consisting of two radiometers (110-162GHz and 164-196GHz) can cover a frequency range of 110-196GHz. The unique and key components to construct this ECE diagnostic instrument are specially-designed detector modules and a diplexer for splitting ECE radiation with high efficiency. The minimum detectable electron temperature with a time response of 1μs is about 0.23eV. The observed signal intensity is roughly consistent with the value estimated by using characteristics of various components (waveguide components, sub-harmonic mixers, amplifiers, and intermediate frequency detectors). In this article, design considerations and preliminary ECE measurements will be described. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

DOI： 10.1585/pfr.6.2402094

Scopus

Publisher：Proceedings - 2010 12th International Conference on Electromagnetics in Advanced Applications, ICEAA'10  

Microwave reflectometric measurement is applied to diagnose human vital signal. The reflectometer signal is processed by a quadrature phase detector in order to obtain both phase and amplitude components of the signal. The phase component is analyzed by using fast-Fourier transform and wavelet transform to evaluate the frequency spectrum of the heartbeat and respiration. In this report, we focus on some challenges such as overnight monitoring and the performance during driving vehicle. The system using Automatic Gain Control (AGC) and integration of reflectometry system are also discussed. ©2010 IEEE.

DOI： 10.1109/ICEAA.2010.5653066

Scopus

Publisher：Review of Scientific Instruments  

A combined system of microwave imaging reflectometry and electron cyclotron emission (ECE) imaging has been developed for the Large Helical Device. This system includes a wide-band two-dimensional horn-antenna mixer array (HMA). The HMA consists of horn antennas, waveguides, mixers, and intermediate frequency circuits. The frequency response of the HMA is between 50 and 110 GHz. The ECE signal is selected using a 95 GHz local oscillator and a 93 GHz high-pass filter. © 2010 American Institute of Physics.

DOI： 10.1063/1.3491223

Scopus

Publisher：Review of Scientific Instruments  

We developed and installed an electron cyclotron emission radiometer for taking measurements of Korea Superconducting Tokamak Advanced Research (KSTAR) plasma. In order to precisely measure the absolute value of electron temperatures, a calibration measurement of the whole radiometer system was performed, which confirmed that the radiometer has an acceptably linear output signal for changes in input temperature. It was also found that the output power level predicted by a theoretical calculation agrees with that obtained by the calibration measurement. We also showed that the system displays acceptable noise-temperature performance around 0.23 eV. © 2010 American Institute of Physics.

DOI： 10.1063/1.3491304

Scopus

Publisher：Review of Scientific Instruments  

A simultaneous projection/detection system of four different frequencies for microwave imaging reflectometry (MIR) was developed for three-dimensional observation of electron density fluctuations in the Large Helical Device (LHD). The microwave with four frequency components at 60.410, 61.808, 63.008, and 64.610 GHz is projected in a continuous-wave mode to illuminate the target LHD plasma. A two-dimensional horn-antenna mixer array (2D HMA) receives the reflected wave from the plasma as well as the wave from the local oscillator operating at 55.800 GHz. The first intermediate frequency (IF) signals at 4.610, 6.008, 7.208, and 8.810 GHz were confirmed to be obtained by downconversion of these microwaves using the 2D HMA. Each of these first IF components is filtered from each other and downconverted again for the superheterodyne detection. It was confirmed that both the amplitudes and the phases of the detected signals reflect the fluctuations in LHD plasmas. © 2010 American Institute of Physics.

DOI： 10.1063/1.3491197

Scopus

Publisher：Review of Scientific Instruments  

A new electron cyclotron emission (ECE) diagnostics system was installed for the Second Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The new ECE system consists of an ECE collecting optics system, an overmode circular corrugated waveguide system, and 48 channel heterodyne radiometer with the frequency range of 110-162 GHz. During the 2 T operation of the KSTAR tokamak, the electron temperatures as well as its radial profiles at the high field side were measured and sawtooth phenomena were also observed. We also discuss the effect of a window on in situ calibration. © 2010 American Institute of Physics.

DOI： 10.1063/1.3491224

Scopus

Publisher：Japanese Journal of Applied Physics  

As the importance of advanced millimeter-wave diagnostics increases, the fabrication of high-performance devices and components becomes essential. In this paper, we describe the development of millimeter-wave planar antennas using low-loss fluorine substrates. The problems to be solved in this study are the low degree of adhesion between copper foil and the fluorine substrate and the accuracy of device pattern using conventional fabrication techniques. In order to solve these problems, a new surface treatment of fluorine films and a fabrication method using electro-fine-forming (EF2) are proposed. In order to confirm the performance of the treated films, microstrip lines (MSLs) and planar patch antennas with a low sidelobe level in the E-plane are designed and fabricated on conventional fluorine substrates and grafted poly(tetrafluoroethylene) (PTFE) films© 2010 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.49.106506

Scopus

Publisher：Review of Scientific Instruments  

Two dimensional (2D) plasma image analysis is useful to study the improvement of plasma confinement in magnetically confined fusion plasmas. We have constructed a 2D interferometer system with phase imaging method for studying 2D plasma density distribution and its fluctuation measurement in the tandem mirror GAMMA 10. 2D profiles of electron density and its fluctuation have been successfully obtained by using this 2D phase imaging system. We show that 2D plasma density and fluctuation profiles clearly depends on the axial confining potential formation with application of plug electron cyclotron heating in GAMMA 10. © 2010 American Institute of Physics.

DOI： 10.1063/1.3464577

Scopus

Publisher：Fusion Science and Technology  

Several types of microwave diagnostics, in the category of electron cyclotron emission (ECE) spectroscopy and reflectometry, have been developed on the Large Helical Device (LHD). Since LHD has a complicated magnetic configuration, the polarization effects have been studied for optimization of the microwave passive and active diagnostics. It was found that if the density is sufficiently high, the effect of mode conversion is negligible and the local polarization angle can be estimated as the angle at the plasma boundary. Three types of ECE spectroscopy, which are the heterodyne radiometer, the Michelson spectrometer, and the grating polychromator, have been optimized and operated routinely in order to measure radial profiles of electron temperature and its fluctuations in the frequency range 50 to 500 GHz. Several types of microwave reflectom-eters have also been utilized for measurements of the electron density profile and fluctuations. Two ultrashort pulsed radar reflectometers for density profile measurements, a V-band frequency-hopping reflectometer for density fluctuation profile measurements, and a fixed-frequency three-channel homodyne reflectometer for the interlock system of the neutral beam injection have been routinely operated. Also, an advanced diagnostic, which uses an imaging technique, has been developed to study the two-or three-dimensional structure of temperature and density fluctuations.

DOI： 10.13182/FST10-A10822

Scopus

Publisher：Journal of Physics: Conference Series  

Reflectometry is considered to be one of the key diagnostics to measure density profiles and density fluctuations of fusion oriented plasmas. When an electromagnetic wave is launched into a plasma, the wave is reflected at the corresponding cutoff layer of the ordinary (O) mode or the extraordinary (X) mode. Reflectometry measures the time of flight (TOF) or group delay of the reflected wave. We have applied ultrashort-pulse reflectometry (USPR) to Large Helical Device (LHD) at National Institute for Fusion Science (NIFS). The highspatial analysis method called signal record analysis (SRA) is utilized to reconstruct the density profiles from the TOF signal. Also, it is noted that the remote control system using super science information network (super-SINET) has been introduced to the present USPR system. This remote system is exclusive, and it seems to be quite effective for collaborating experiment of large devices such as ITER. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/227/1/012034

Scopus

Publisher：34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009  

Millimeter wave imaging diagnostics such as electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry (MIR) are advanced technology to investigate electron temperature/density profiles and their fluctuations in magnetically confined plasmas. We have installed an ECEI system in the large helical device (LHD) at National Institute for Fusion Science (NIFS). The optimization of a receiving antenna array is essential for the imaging diagnostics. We have designed and fabricated dual-dipole antenna array. In this paper, the design and fabrication process of dual-dipole antennas are described. The characterizations of the antennas are also reported by comparing simulation and experimental results. © 2009 IEEE.

DOI： 10.1109/ICIMW.2009.5324955

Scopus

Publisher：34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009  

We have developed an electron cyclotron emission (ECE) radiometer to measure the radial electron temperature profiles. Before installation of this system on KSTAR, we installed a part of this system on LHD, and confirmed that acquired signals are in good agreement with those provided by the Michelson spectrometer. © 2009 IEEE.

DOI： 10.1109/ICIMW.2009.5325633

Scopus

Publisher：Plasma Devices and Operations  

Microwave to millimeter-wave diagnostic techniques such as interferometry, reflectometry, scattering and radiometry have been powerful tools for diagnosing magnetically confined plasmas. Recent advances in electronic devices and components together with computer technology have enabled the development of advanced diagnostics in microwave to millimeter-wave region. The two-dimensional and three-dimensional profiles of plasma density/temperature and dynamic behaviors of their fluctuations are measured by using the advanced diagnostic systems. The measurements have clarified the physics issues such as stability, wave phenomena and fluctuation-induced transport. We report here on the representative microwave diagnostics and their contribution to plasma confinement physics. © 2009 Taylor & Francis.

DOI： 10.1080/10519990902909436

Scopus

Publisher：International Conference on Communication Technology Proceedings, ICCT  

Reflectometry is widely used to measure plasma density profiles and density fluctuations in magnetically confined plasmas. When the electromagnetic wave is launched into the plasma, the wave is reflected at the corresponding cutoff layer. Higher frequency wave reflects at the higher density layer. Therefore wide frequency band system is needed to obtain whole density profile. Ultrashort-pulse as a source is one of the candidates to achieve this, which is called ultrashort-pulse reflectometry (USPR). An USPR has been applied to Large Helical Device (LHD) at National Institute for Fusion Science (NIFS). The system can be controlled from remote site via Internet called Super-SINET. This paper describes the USPR system and the reconstruction method of density profiles. © 2008 IEEE.

DOI： 10.1109/ICCT.2008.4716254

Scopus

Publisher：International Conference on Communication Technology Proceedings, ICCT  

An ultrashort-pulse radar (USPR) has been developed for non-destructive inspection of structures, search of buried objects, and biomedical imaging. An impulse with 150 ps pulse width is used as a source for the present USPR. Since the bandwidth of the source is inverse relation to the pulse width, we can expect wide frequency range in microwave region which benefits high spatial resolution as well as time resolution. Therefore antennas for the USPR are required to provide acceptable characteristic in wide frequency band width. Nondestructive inspection for concrete structures utilizes the contrast in the dielectric properties between cement and air at cracks. In this paper, the comparison of inspected results of the concrete samples are described using three types of antennas, an openended rectangular waveguide antenna, a bow-tie antenna, and a log-spiral antenna. © 2008 IEEE.

DOI： 10.1109/ICCT.2008.4716255

Scopus

Publisher：International Conference on Communication Technology Proceedings, ICCT  

As the importance of advanced microwave and millimeter-wave diagnostics increases, the fabrications of highperformance planar devices become essential. This paper describes the development of planar devices such as antennas using low-loss fluorine materials. The problems to be solved for the present purpose are the low degree of adhesion between copper foil and fluorine substrate and the accuracy of device pattern using conventional fabrication techniques. In order to solve these problems, surface treatment of fluorine films and a fabrication method using Electro-Fine-Forming (EF2) are proposed. The peel adhesion strength between the metal and the fluorine films and the value of dielectric constant of the fluorine films before and after grafting are reported. In order to confirm the performance of the treated films, microstrip lines are fabricated on the conventional fluorine substrates and on the grafted-PTFE (Polytetrafluoroethylene) films. The prototype antennas using fluorine substrates with EF2 fabrication technique are also introduced. © 2008 IEEE.

DOI： 10.1109/ICCT.2008.4716223

Scopus

Publisher：Proceedings of 2008 Asia Pacific Microwave Conference, APMC 2008  

DOI： 10.1109/APMC.2008.4957984

Scopus

Publisher：Review of Scientific Instruments  

Three key devices of the microwave imaging reflectometry (MIR) are under development in large helical device (LHD). The 2-D mixer array is developed by stacking the one-dimensional array of the planar Yagi-Uda antenna. The new type of the bandpass filter bank is modified to match the requirement of the MIR. The low-cost quadrature demodulator is also developed for the phase detection system. By using the low-price commercial wireless devices, the development cost becomes much lower than the expensive waveguide system. These devices enable the development of 2-D/3-D microwave imaging system for the plasma diagnostics and industrial applications. © 2008 American Institute of Physics.

DOI： 10.1063/1.2993741

Scopus

Publisher：Review of Scientific Instruments  

Plasma experiments on KSTAR are scheduled to start up this year (2008). We have developed an electron cyclotron emission (ECE) radiometer to measure the radial electron temperature profiles in KSTAR experiments. The radiometer system consists, briefly, of two downconversion stages, amplifiers, bandpass filter banks, and video detectors. These components are made commercially or developed in house. The system detects ECE power in the frequency range from 110 to 196 GHz, the detected signal being resolved by means of 48 frequency windows. Before installation of this system on KSTAR, we installed a part of this system on large helical device (LHD) to study the system under similar plasma conditions. In this experiment, the signal amplitude, considered to be proportional to the electron temperature, is measured. The time-dependent traces of the electron temperature measured by this radiometer are in good agreement with those provided by the LHD Michelson spectrometer. The system noise level which limits the minimum measurable temperature (converted to the electron temperature) is about 30 eV. © 2008 American Institute of Physics.

DOI： 10.1063/1.2966380

Scopus

Publisher：Review of Scientific Instruments  

Reflectometry has been expected to be one of the key diagnostics to measure density profiles. We have applied an ultrashort-pulse reflectometry (USPR) system to Large Helical Device in the National Institute for Fusion Science. Wide frequency band system is required to obtain wide density profile since an incident wave is reflected at the density layer corresponding to its cutoff frequency. The reflectometry utilizes an impulse with less than [formula omitted] pulse width as a source. Since the bandwidth of an impulse has an inverse relation to the pulse width, we can cover the frequency range of micro- to millimeter waves [formula omitted] with a single source. The density profiles can be reconstructed by collecting time-of-flight (TOF) signals for each frequency component of an impulse reflected from the corresponding cutoff layer. We utilize the signal record analysis (SRA) method to reconstruct the density profiles from the TOF signal. The effectiveness of the SRA method for the profile reconstruction is confirmed by a simulation study of the USPR using a finite-difference time domain method. © 2008, American Institute of Physics. All rights reserved.

DOI： 10.1063/1.2953683

Scopus

Publisher：Japanese Journal of Applied Physics  

As the importance of advanced millimeter-wave diagnostics increases, a reliable and accurate fabrication technique for highperformance devices and relevant components is essential. We describe a new improved fabrication technique for millimeterwave planar components, such as antennas using low-loss fluororesin substrates. A fragile adhesion between the copper foil and fluororesin substrate and the accuracy of the device pattern using conventional fabrication techniques have been prime suspects in the failure of the devices. In order to solve these problems, surface treatment of fluororesin films and a fabrication method using electro-fine-forming (EF2) are proposed. The peel adhesion strength between the metal and fluororesin films and the value of the dielectric constant of the fluororesin films before and after grafting are reported. A prototype antenna using conventional fluororesin substrates and grafted-poly(tetrafluoroethylene) (PTFE) films produced using the EP2 fabrication technique are also introduced. ©2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.4755

Scopus

Publisher：Fusion Science and Technology  

Microwave/millimeter-wave techniques such as interferometry, reflectometry, scattering, and radiometry have been powerful tools for diagnosing magnetically confined high-temperature plasmas. Important plasma parameters were measured to clarify the physics issues such as stability, wave phenomena, and fluctuation-induced transport. Recent advances in microwave and millimeter-wave technology together with computer technology have enabled the development of new generation of diagnostics for visualization of 2D and 3D structures of plasmas. Microwave/Millimeter-wave imaging is expected to be one of the most promising diagnostic methods for this purpose. We report here on the recent progress in microwave diagnostics and the results obtained in magnetically confined plasmas.

DOI： 10.13182/fst07-a1312

Scopus

Publisher：Fusion Science and Technology  

Plasma density measurements are one of the important studies for achievement of nuclear fusion reaction. We have studied plasma electron density distributions and plasma frequency fluctuation by using microwave interferometers etc. in GAMMA 10. We show the first results of 2-dimensional plasma density distributions measurement under some conditions of the electron cyclotron resonance heating microwave power in GAMMA 10.

DOI： 10.13182/fst07-a1374

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

Microwave reflectometric measurement is applied to diagnose vital signal of a human. The reflectometer signal is processed by a quadrature phase detector in order to obtain both phase and amplitude components of the signal. The phase component is analyzed by using fast-Fourier transform and wavelet transform to evaluate the frequency spectrum of the heartbeat and respiration. Various applications of the microwave measurement are discussed.

DOI： 10.1109/APMC.2007.4554892

Scopus

Publisher：IRMMW-THz2007 - Conference Digest of the Joint 32nd International Conference on Infrared and Millimetre Waves, and 15th International Conference on Terahertz Electronics  

As the importance of intelligent transport system (ITS) and imaging diagnostics increases, the fabrication of high performance millimeter-wave planar components becomes essential. This paper describes the development of high performance millimeter-wave planar components such as antennas using a low-loss fluorine substrate. The problems to be solved are the low degree of adhesion between copper foil and the fluorine substrate and the shape of the antenna pattern. In order to solve the problems, surface treatment of fluorine films and a fabrication method using Electro Fine Forming (EF2) are utilized.

DOI： 10.1109/icimw.2007.4516733

Scopus

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers  

Poly(tetrafluoroethylene) (PTFE) and perfluoroethylene-propylene (PFEP) have many desirable properties for application to electronic devices, such as low dielectric constant and loss tangent. However, the weak adhesion of the polymer to various metals, associated with the chemical inertness of the fluorine resin surface, fails to satisfy many of the industry requirements. Surface treatment of PTFE and PFEP by radiation-induced graft polymerization was carried out to improve the adhesion. Peel adhesion strengths of 10.3 and 1.4.5 N/cm were attained for PTFE/Cu and PFEP/Cu, respectively by the treatment. In addition, the dielectric function of grafted PTFE and grafted PFEP remained almost unchanged after the graft polymerization. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.9244

Scopus

Publisher：Proceedings - Symposium on Fusion Engineering  

This paper presents recent experimental results in the Large Helical Device (LHD), which is the world largest helical system (Rax ∼ 3.6 m, aav ∼ 0.6 m, Bax ∼ 2.75 T) and has capability of steady state operation because of the super conducting magnets. LHD confines the plasma with Tio ∼ 2 keV and ne ∼ 0.8 x 1019 m -3 for 1905 sec using the ICRF heating. In this case, the total plasma heating energy was ∼ 1.3 GJ. This indicates that high energy ions generated by ICRF is well confined. Large magnetic island in the vacuum field due to the error field is vanished in plasma with higher temperature or with higher beta, so the error field is not an issue in helical systems. The obtained averaged beta is more than 4.3 % in LHD. Since the beta is not limited by the MHD events or magnetic island but the beta is limited by the lack of heating power, further improvement of beta can be expected. Internal and external transport barrier have been also observed, and the electron temperature and the ion temperature exceed 10 keV in the improved confinement mode in LHD. Besides the potential of the disruption free steady stated operation, LHD experiment accumulates evidences so that fusion reactor becomes more realistic. © IEEE.

DOI： 10.1109/FUSION.2005.252854

Scopus

Publisher：IRMMW-THz 2006 - 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics  

The development of high performance millimeter-wave planar antennas using low-loss fluorine substrate is reported. The problems to be solved are low degree of adhesion between copper foil and fluorine substrate and shape of antenna pattern. In order to solve the problems, surface treatment of fluorine substrate and a fabrication method using Electro Fine Forming (EF2) are described. ©2006 IEEE.

DOI： 10.1109/ICIMW.2006.368476

Scopus

Publisher：Review of Scientific Instruments  

An ultrashort-pulse reflectometer (USPR) has been applied to the large helical device plasmas in National Institute for Fusion Science for edge density profile measurement. Remote control system using super science information network has been introduced to the USPR system. The remote console at Kyushu University having graphical user interface is prepared to control the instruments of the USPR via the general-purpose interface bus. The operations such as the adjustment of supply voltage fed to amplifiers and the frequency doubler, timing control of the impulse, data acquisition, and monitoring can be performed from the remote site. The position of transmitter and receiver antennas can also be controlled remotely in order to observe the cutoff layer depending on various plasma conditions. The directly recorded signal by a sampling scope is analyzed and reconstructed by means of the signal record analysis method. © 2006 American Institute of Physics.

DOI： 10.1063/1.2220081

Scopus

Publisher：Review of Scientific Instruments  

A multichannel reflectometry with an imaging optical system is under development for the measurement of the electron density fluctuations in the Large Helical Device (LHD). The right-hand cutoff layer is utilized as a reflection surface. The angle of an ellipsoidal mirror installed inside the vacuum chamber is remotely adjustable with the ultrasonic motor in order to optimize the illumination angle for the wider range of the plasma parameters. An oscillation due to density fluctuation was observed using the microwave imaging reflectometry for the first time in LHD plasma experiment. © 2006 American Institute of Physics.

DOI： 10.1063/1.2349749

Scopus

Publisher：Fusion Engineering and Design  

Control, data acquisition, plasma monitoring and remote participation for steady state operation in the large helical device (LHD) are reviewed. By controlling the impedance matching of ICH, the plasma position and the electron density, high temperature plasma is confined for 1905s. The plasma parameters are monitored in real time. Data are continuously sampled by the YOKOGAWA WE7000 system and by the NATIONAL INSTRUMENTS CompactPCI system. Those data are managed by the object-oriented database system based on ObjectStore in distributed servers with mass storage. By using the multi protocol label switching-virtual private network (MPLS-VPN) technology, the local area network of LHD is expanded to the Japanese fusion community. This provides the remote participants with the same environment of the LHD control room. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.fusengdes.2006.04.027

Scopus

Publisher：Thin Solid Films  

We have applied an ultrashort-pulse reflectometer (USRM) to an inductively coupled plasma for density profile measurement along with a plasma absorption probe (PAP). It is found that the density in the edge plasma region measured by USRM is in good agreement with that by PAP, however, the measured density in core region shows large discrepancy between two methods. This difference is considered to occur due to difference of optical path route within utilized frequency band. We have rearranged experimental setup to avoid this improper situation, and confirmed that the density in core region measured by both methods is becoming in good agreement. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.08.050

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

Polytetrafluoroethylene (PTFE) has many desirable properties for substrates of millimeter-wave planar antennas such as low dielectric constant and loss tangent. However, it has weak adhesion to various metals. Surface treatment of PTFE via radiation-induced graft polymerization was carried out to improve the adhesion. The peel adhesion strength of the PTFE/Cu was attained to be 10.3 N/cm by the treatment. The dielectric function of grafted-PTFE remained almost unchanged after the graft polymerization. The design and fabrication of millimeter-wave antennas on the treated PTFE substrates have been performed using electro-fine-forming (EF2) technology. Copyright 2006 IEICE.

DOI： 10.1109/APMC.2006.4429810

Scopus

Publisher：The Joint 30th International Conference on Infrared and Millimeter Waves and 13th International Conference on Terahertz Electronics, 2005. IRMMW-THz 2005  

We have been developing a detector element which include dipole antennas and a doubly balanced mixer fabricated on a dielectric substrate. This detector is designed for millimeter-wave imaging system on fusion device experiment in order to measure electron temperature distribution. Prototype detector which work in X-band shows ideal characteristics such as axisymmetric field pattern and detection sensitivity as an imaging element. Recently, we have fabricated same type detectors which work in E-band range. We have confirmed that the detectors have sensitivity in this frequency range. © 2005 IEEE.

Scopus

Publisher：Fusion Science and Technology  

Applicability of microwave imaging reflectometry (MIR) for the case of mirror device was numerically studied. The questions concerning radial localization of measurements, optimal position of optical system and imaging properties of MIR system were considered. The high curvature of the plasma cutoff layer and a relatively small distance from the plasma to the port are known to improve the performance of a conventional reflectometer. Nevertheless in the case of density fluctuations with wide wavenumber spectrum and large amplitude, the imaging reflectometry shows better results than the conventional one.

DOI： 10.13182/FST05-A635

Scopus

Publisher：Proceedings - Symposium on Fusion Engineering  

This paper presents development of quasi-optical microwave technology for ECE and reflectometry diagnostics in the Large Helical Device (LHD). The ECE for the electron temperature measument is transmitted with the corrugated wave guide system. Technology for Microwave imaging, sucn as imaging reflectometry and ECE imaging, has been developed to visualize 3D view of turbulence. © IEEE.

DOI： 10.1109/FUSION.2005.252969

Scopus

Publisher：Review of Scientific Instruments  

In this article we perform a numerical study of microwave imaging reflectometry (MIR) and compare it with conventional reflectometry system. As an approximation to the reflections by real plasma fluctuations, a corrugated wheel is used. As far as general performance is concerned, our simulations confirm the results by Munsat et al. [Plasma Phys. Controlled Fusion 45, 469 (2003)] that the MIR system reproduces shape of corrugation far from the wheel while conventional systems fail to do so. We addressed the effects of asymmetry and defocusing of the wheel-reflectometer system as well as spectral sensitivity of the imaging reflectometer. For a particular geometry we estimated the deterioration of the MIR performance due to misalignments and existence of broadband fluctuations. ©2004 American Institute of Physics.

DOI： 10.1063/1.1788850

Scopus

Publisher：Review of Scientific Instruments  

We have applied an ultrashort-pulse reflectometer to large helical device plasmas for density profile measurement. The frequency range of the impulse is up-converted into the R band, which corresponds to the cutoff frequency of edge plasma region in the ordinary mode. The reflected wave from plasma is received and directly recorded by a sampling scope. This system can be controlled and monitored from remote site (Kyushu University) by using ultrawideband science information network (super-SINET) that ideal bandwidth reaches up to 1 Gbps. As a result of the measurement, we have confirmed reflection wave from the plasma when the plasma density reaches steady state during the measurement. © 2004 American Institute of Physics.

DOI： 10.1063/1.1786645

Scopus

Publisher：Plasma Physics and Controlled Fusion  

Standard diagnostics for fundamental plasma parameters and for plasma physics are routinely utilized for daily operation and physics studies in the large helical device (LHD) with high reliability. Diagnostics for steady-state plasma are under intensive development, especially for Te, ne (yttrium-aluminium garnet (YAG) laser Thomson, CO2 laser polarimeter), data acquisition in steady-state and heat-resistant probes. To clarify the plasma properties of the helical structure, two- or three-dimensional diagnostics are being aggressively developed: tangential cameras (fast SX TV, photon counting CCD, Hα TV); tomography (tangential SX CCD, bolometer); imaging (bolometer, ECE, reflectometer). Divertor and edge physics are important key issues for steady-state operation. Diagnostics for neutral flux (Hα array, Zeeman spectroscopy) and ne (fast scanning probe, Li beam probe, pulsed radar reflectometer) are also in advanced stages of development. In addition to these, advanced diagnostics are being intensively developed in LHD through domestic and international collaborations.

DOI： 10.1088/0741-3335/45/12A/027

Scopus

Publisher：IEEE International Conference on Plasma Science  

The ultrashort-pulse refrectometer (USRM) system is being prepared to apply to Large Helical Device (LHD). At the present time, we preliminary applied this USRM system to a metal plate as a target, and confirmed that detection time of the reflected pulse is delayed proportionally as increasing in double path length. Recently, we are constructing the USRM system at National Institute for Fusion Science (NIFS). The experiment using this USRM system will be performed since February this year. The USRM system for LHD is as follows. The system utilize an impulse generator as a source, which can transmit an impulse with a pulse width of 22 ps and a voltage amplitude of 3 V. The impulse is fed to an active frequencydoubler via a WD-750 waveguide and a low loss coaxicial cable to produce higher frequency component suitable for high density plasma such as LHD plasma. The charped millimeter wave is amplified by a wide band power amplifier and transmitted by a conical horn in ordinary (O) mode. We utilize optical lenses in front of the transmitter and the receiver. The reflected wave is received by the receiver horn and amplified by low-noise amplifiers. The signal is recorded directly by a high-speed sampling scope (50 GSample/s). The repetition rate of impulse transmission is fixed at 1GHz, and data acquisition is completed for 10 ms. In the analysis for reconstructing density profile from the signal, we utilize signal record analysis (SRA) method, which can introduce less receiver channel requirements and reliable profile reconstruction. The SRA is the method that utilizes a phase difference at each frequency between presence and absence of plasma rather than a time delay at each frequency. In the conference, we will report the result of application of the USRM system to LHD.

Scopus

Publisher：Review of Scientific Instruments  

An ultrashort-pulse reflectometry (USRM) for steady-state plasmas was discussed. A frequency upconverter and an active doubler were utilized for the the generation of the pulse with higher frequency up to 90 GHz. The generation of the upconverted pulse in the range of 60-90 GHz and the second-harmonic frequency in the range of 26-40 GHz was confirmed.

DOI： 10.1063/1.1530351

Scopus

Publisher：Review of Scientific Instruments  

A study was performed on the measurements of density fluctuations in reflectometry of cylindrical plasmas. A fluctuation reflectometry model capable of handling the plasma profiles of arbitrary shape and curvature was developed. The advantage of the analytical model was its simplicity and low consumption of computational resources.

DOI： 10.1063/1.1538355

Scopus

Publisher：Review of Scientific Instruments  

The electron cyclotron emission (ECE) imaging system for the large helical device (LHD) was presented. The imaging system consists of optics installed inside the vacuum chamber of LHD. The ECE signals were down-converted at the mixers and the IF signal was fed to a filter bank.

DOI： 10.1063/1.1530384

Scopus

Publisher：Plasma Physics and Controlled Fusion  

The results of an analytical treatment of the time-dependent 2D full-wave equation are presented here for the case of ultra-short pulse (USP) reflectometry. We consider several models of the plasma geometry, namely linear and nonlinear slab models, as well as a 2D plasma density profile with cylindrical symmetry. The latter model is more realistic when compared to the 1D stratified plasma models previously employed in all the analytical, and most numerical, treatments, since the plasma in fusion toroidal devices, mirror machines and plasma processing chambers can often be considered axially symmetric on the scale relevant to microwave reflectometry. Based on the results of analytical modelling, a signal record analysis method of profile reconstruction is proposed. The method has the advantage of using raw signal records instead of poorly localized frequency modes, which makes it robust for the profile measurements using USP reflectometry.

DOI： 10.1088/0741-3335/43/10/305

Scopus

Publisher：Review of Scientific Instruments  

In the GAMMA10 tandem mirror, a strong ion cyclotron range of frequency heating is performed. As a result of the heating, the Alfvén ion cyclotron (AIC) modes are spontaneously excited due to the strong temperature anisotropy. The AIC modes in the GAMMAlO are excited as the axial eigenmodes and detected at the whole of the device. In the recent experiments, the clear standing wave structure is observed with the magnetic probe measurements. Characteristics of the AIC modes and the measurement of the axial profile are presented. © 2001 American Institute of Physics.

DOI： 10.1063/1.1309008

Scopus

Publisher：Fusion Technology  

Two types of microwave reflectometries are installed in the GAMMA 10 device for electron density profile and fluctuation measurement. By trying several methods of frequency analysis, the distribution of fluctuation is simultaneously observed. Furthermore, magnetic fluctuation is observed by cross-polarization scattering method.

DOI： 10.13182/fst01-a11963457

Scopus

Publisher：Review of Scientific Instruments  

A numerical simulation of cross-polarization scattering (CPS) was performed by using frequency dependent finite difference time domain [(FD)2TD] method. In the CPS process, an incident ordinary (extraordinary) wave is converted to an extraordinary (ordinary) wave by magnetic fluctuations in a plasma. It is confirmed in the simulation that an incident wave propagates in an anisotropic dispersive media properly. The relation between scattered electric field and magnetic fluctuations is also obtained. © 2001 American Institute of Physics.

DOI： 10.1063/1.1309000

Scopus

Publisher：Review of Scientific Instruments  

A cross-polarization scattering (CPS) diagnostic method was applied to the GAMMA10 tandem mirror in order to study electromagnetic plasma waves with frequency less than 10 MHz. In the CPS process, an incident ordinary (extraordinary) wave is converted to an extraordinary (ordinary) wave by magnetic fluctuations in a plasma. The frequency spectra, and the density and magnetic fluctuations of the waves can be evaluated from both the CPS and reflectometry. The converted wave propagates through the cutoff layer and reaches a different diagnostic port with a receiver horn. The observed waves are identified as the electromagnetic drift wave assuming the wave number matching condition. The low frequency waves nonlinearly coupled with the Alfven ion cyclotron waves are also observed with increase in the plasma pressure. © 1999 American Institute of Physics.

DOI： 10.1063/1.1149423

Scopus

Publisher：Review of Scientific Instruments  

Numerical simulations of frequency modulation (FM) reflectometry are carried out for the effects of density fluctuations on phase measurements. It is found that the fluctuation amplitude, the fluctuation frequency, the sweep time of a source, and the beat frequency of a mixer output play the important roles. The reliability of density profile measurement is investigated for various sweep times and local path lengths. It is demonstrated that the reconstructed density profiles seem to be improved when the sweep time is faster than 100 μs and the local path length is shorter than 1 m. The numerical simulations are compared with the experimental results obtained from a broadband FM reflectometer applied to the GAMMA 10 tandem mirror. © 7999 American Institute of Physics.

DOI： 10.1063/1.1149499

Scopus

Publisher：Fusion Technology  

The microwave reflectometry using FM and ultrashort-pulse radar techniques have been applied to GAMMA 10 in order to diagnose plasma density profile and fluctuations. The reliability of profile measurement using the FM reflectometer is investigated for various sweep times and local path length. It is demonstrated that the reconstructed density profiles seem to be improved when the sweep time is faster than 50-100 μs. The several reconstruction algorithms are introduced to analyze the fast time-varying data, such as, the maximum-entropy method and wavelet analysis as well as zero-cross fringe counting and digital complex demodulation method. The reflectometers are applied to the measurement of density/magnetic fluctuations. The space-and time-resolving spectra of rf waves as well as low-frequency waves are obtained. The density and magnetic-field fluctuations are evaluated from both the reflectometer and cross-polarization scattering diagnostic method.

DOI： 10.13182/fst99-a11963853

Scopus

Publisher：Physical Review Letters  

Increases in the flux and temperature of end-loss electrons are observed following excitation of an Alfvén ion cyclotron (AIC) mode in the GAMMA 10 tandem mirror. Electron loss power carried to an end wall becomes more than twice as large as that without the AIC mode. The increases in the electron flux and temperature are observed only when the parallel phase velocity of the AIC mode matches with the electron thermal velocity, strongly suggesting that the parallel electron acceleration is due to electron Landau damping of the AIC mode. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevLett.82.1169

Scopus

Publisher：Japanese Journal of Applied Physics, Part 2: Letters  

Cross-polarization scattering (CPS) diagnostic was applied to the central-cell plasma of the GAMMA 10 tandem mirror in order to study electromagnetic plasma waves with frequencies of less than 200 kHz. In the CPS process, an incident ordinary (extraordinary) wave is converted to an extraordinary (ordinary) wave by magnetic fluctuations in a plasma. The converted wave propagates through the cutoff layer and reaches the opposite diagnostic port. The experimental data suggest that the power spectral density of the CPS signal satisfies the Bragg condition, while the reflectometer detects the waves near the cutoff layer where the wave number cannot be resolved.

DOI： 10.1143/jjap.36.l587

Scopus

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Publisher：Japanese Journal of Applied Physics, Part 2: Letters  

Cross-polarization scattering (CPS) diagnostics using ultrashort pulse microwaves is applied to the GAMMA 10 tandem mirror for the measurement of internal magnetic fluctuations. The CPS process uses the mode conversion effect of electromagnetic waves by means of magnetic fluctuations in a plasma. The mode contamination of antennas and multiple reflections from the vacuum vessel make the CPS measurement difficult since they easily mask the CPS signal. By using polarizers and performing time-of-flight measurement on the ultrashort pulse, the spurious electromagnetic waves are eliminated and the identification of the CPS process is successful.

DOI： 10.1143/jjap.40.l841

Scopus

Event date： 2017.12

Event date： 2017.9

Event date： 2012.11

Venue：クローバプラザ、春日市  

Event date： 2012.11

Venue：クローバプラザ、春日市  

Event date： 2012.8

Venue：つくば市　エポカルつくば  

Event date： 2012.8

Event date： 2012.8

Venue：Seogwipo Training Center of Jeju National University, Korea  

Event date： 2012.6

Venue：神戸、神戸国際会議場  

Event date： 2012.5

Venue：Monterey, CA, USA  

Event date： 2012.5

Venue：Monterey, CA, USA  

Event date： 2012.5

Venue：Monterey, CA, USA  

Event date： 2010.12

Event date： 2010.5

Event date： 2010.5

Event date： 2010.5

Event date： 2009.12

Event date： 2009.12

Event date： 2009.12

Event date： 2009.12

Event date： 2009.12

Event date： 2009.12