[show abstract][hide abstract] ABSTRACT: “Fusion virtual laboratory (FVL)” is the experiments’ collaboration platform covering multiple fusion projects in Japan. Major Japanese fusion laboratories and universities are mutually connected through the dedicated virtual private network, named SNET, on SINET4. It has 3 different categories; (i) LHD remote participation, (ii) bilateral experiments’ collaboration, and (iii) remote use of supercomputer. By extending the LABCOM data system developed at LHD, FVL supports (i) and (ii) so that it can deal with not only LHD data but also the data of two remote experiments: QUEST at Kyushu University and GAMMA10 at University of Tsukuba. FVL has applied the latest “cloud” technology for both data acquisition and storage architecture. It can provide us high availability and performance scalability of the whole system. With a well optimized TCP data transferring method, the unified data access platform for both experimental data and numerical computation results could become realistic on FVL. The FVL project will continue demonstrating the ITER-era international collaboration schemes and the necessary technology.
Fusion Engineering and Design. 12/2012; 87(12):2189–2193.
[show abstract][hide abstract] ABSTRACT: This paper presents a system called “TSMAP” that maps electron temperature profiles to flux coordinates for the Large Helical Device (LHD). Considering the flux surface is isothermal, TSMAP searches an equilibrium database for the LHD equilibrium that fits the electron temperature profile. The equilibrium database is built through many VMEC computations of the helical equilibria. Because the number of equilibria is large, the most important technical issue for realizing the TSMAP system is computational performance. Therefore, we use multiple personal computers to enhance performance when building the database for TSMAP. We use virtual machines on multiple Linux computers to run the TSMAP program. Virtual machine technology is flexible, allowing the number of computers to be easily increased. This paper discusses how the use of virtual machine technology enhances the performance of TSMAP calculations when multiple CPU cores are used.
Fusion Engineering and Design. 12/2012; 87(12):2076–2080.
[show abstract][hide abstract] ABSTRACT: A novel configuration of the multi-pass Thomson scattering (TS) system is proposed to improve the time resolution and accuracy of electron temperature measurements by use of a polarization control technique. This configuration can realize a perfect coaxial multi-passing at each pass, and the number of round trips is not limited by the optical configuration. To confirm the feasibility of the new method, we installed this system in the GAMMA 10 plasma system. As a result, the integrated scattering signal of the double-pass configuration is about two times larger than that of the single-pass configuration. These results are in good agreement with the design.
The Review of scientific instruments 10/2012; 83(10):10E326. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: In order to measure the poloidal rotation velocity, a Doppler reflectometer has been developed in Large Helical Device (LHD). A remotely controlled antenna tilting system has been installed in an LHD vacuum vessel. A synthesizer is used as the source, and the operation microwave frequency ranges are ka-band and V-band. In LHD last experimental campaign we obtained the Doppler shifted signal, which was consistent with CXRS measurements.
The Review of scientific instruments 10/2012; 83(10):10E322. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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.
The Review of scientific instruments 10/2012; 83(10):10E347. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the GAMMA 10 tandem mirror, the typical electron density is comparable to that of the peripheral plasma of torus-type fusion devices. Therefore, an effective method to increase Thomson scattering (TS) signals is required in order to improve signal quality. In GAMMA 10, the yttrium-aluminum-garnet (YAG)-TS system comprises a laser, incident optics, light collection optics, signal detection electronics, and a data recording system. We have been developing a multi-pass TS method for a polarization-based system based on the GAMMA 10 YAG TS. To evaluate the effectiveness of the polarization-based configuration, the multi-pass system was installed in the GAMMA 10 YAG-TS system, which is capable of double-pass scattering. We carried out a Rayleigh scattering experiment and applied this double-pass scattering system to the GAMMA 10 plasma. The integrated scattering signal was made about twice as large by the double-pass system.
The Review of scientific instruments 10/2012; 83(10):10E333. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: To measure the Z(eff) with electron temperature (T(e)) and electron density (n(e)) profiles at the same time and the same position in the KSTAR tokamak, we design a new polychromator for Thomson scattering system that has additional function. The additional function is measuring bremsstrahlung intensity to calculate Z(eff) independent of Thomson signals. For this new polychromator, we design and fabricate a collimation lens set, and interference filter that has center wavelength of 523 nm and 2 nm FWHM. Finally, we change the lenses, detector diodes, and add the bremsstrahlung filter on the KSTAR edge Thomson scattering polychromator. Then this new polychromator was tested by Tungsten light and monochromator.
The Review of scientific instruments 10/2012; 83(10):10E334. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: New power records of second harmonic gyrotron oscillation have been demonstrated in the sub-THz band. The first step gyrotron of demountable type had succeeded in oscillation with power more than 50 kW at 350 GHz and nearly 40 kW at 390 GHz [T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009)]. Then, the second step gyrotron of sealed-off type was manufactured. A cavity mode was carefully selected to avoid mode competition with a neighboring fundamental harmonic mode. Matching of the selected mode with the electron gun was also circumspectly considered. The second step gyrotron has attained higher power radiation than the first gyrotron. The maximum single mode power was 62 kW at 388 GHz. Then, the electron gun was modified for use of a different cavity mode with a higher coupling coefficient than that for the 62 kW mode. The new mode proved single mode oscillation power of 83 kW at about 389 GHz. These results are new second-harmonic-oscillation power records for sub-THz gyrotrons. The present study constitutes foundations of development of high power second harmonic sub-THz gyrotron for application to collective Thomson scattering measurement on fusion plasmas, especially on high-density plasmas such as those produced in LHD [N. Ohyabu et al., Phys. Rev. Lett. 97, 055002 (2006)]. This paper reports the design consideration to realize high power single mode gyrotron oscillation at second harmonic and the examination of oscillation characteristics of the gyrotron.
Physics of Plasmas 06/2012; 19(6). · 2.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: Macro-scale temperature fluctuations, which have long radial correlation
length (of the order of the plasma radius), have been discovered on
Large Helical Device (LHD). In this paper, non-linear coupling between
the long-range fluctuations and microscopic fluctuations is investigated
using cross bi-coherence analysis. The significant cross bi-coherence
between long-range fluctuations and micro-fluctuations is observed in
the range of frequency f < 100 kHz, where f is the frequency of
microscopic fluctuations. It is found that the squared bi-coherence and
bi-phase for this three-wave coupling is weakly dependent on the
frequency of microscopic fluctuations. These observations demonstrate
that the microscopic fluctuations are coherently interacting with
Journal of the Physical Society of Japan 03/2012; 81(3):4501-. · 2.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: Electron temperature fluctuations with long-distance correlation have been discovered in LHD. This paper reports the extended observations recently made on the spatiotemporal structure of the long-range fluctuations both in quasi-stationary and transient plasmas. The detailed characteristics or spatiotemporal characteristics of long-range temperature fluctuations are revealed successfully using correlation analysis. Particularly, the dynamics of the long-range fluctuations is investigated to find that the amplitude of the fluctuations decreased and their radial correlation lengths shortened during the transient phase induced by pellet injection. Temporal changes of radial correlation structure and amplitude of fluctuations at the onset of change in the plasma state are discussed.
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Instrumentation 01/2012; 7(01):C01089. · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: A dispersion interferometer is free from mechanical vibrations, which
cause measurement errors. Hence, a vibration compensation system is not
required and the interferometer is suitable for future large fusion
reactors. We propose a combination of phase modulation and the use of a
ratio of modulation amplitudes for phase extraction to improve the phase
resolutions, which are evaluated during bench testing. The design of the
optical system for the Large Helical Device is shown.
Journal of Instrumentation 01/2012; 7(01):C01055. · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Two color laser diagnostics using THz laser sources are under development for a high performance operation of the Large Helical Device and for future fusion devices such as ITER. So far, we have achieved high power laser oscillation lines simultaneously oscillating at 57.2 μm (1.6 W) and 47.7 μm (0.8 W) by using a twin optically-pumped CH3OD laser. And, we confirmed the usefulness of this two color laser operation for two-color laser interferometry in a test stand. For the measurement of the Faraday rotation angle we have developed a photo-elastic modulator (PEM) operating around 50 μm, and performed bench tests of the polarimeter with dual PEMs and demonstrated the feasibility of the polarimeter. The achieved angular resolution is 0.01 degrees with a time resolution of 1 ms, which satisfies diagnostic requirements for q-profile measurements on ITER (0.05 deg. at 10 ms time resolution). In this symposium, recent hardware developments and simultaneous measurements of a phase shift and a rotation angle will be presented.
Journal of Instrumentation 01/2012; 7(02). · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Maintaining the reflectivity of first mirrors is indispensable in future fusion devices. While a retroreflector (corner cube mirror) is useful for laser diagnostics, impurities tend to accumulate and form a thick deposition layer in the central region, which causes degradation of reflectivity, due to the hollow shape of the retroreflector. Two mirror structures are tested to retain the reflectivity in the Large Helical Device (LHD). One is a bending mirror structure with a protective cylinder with fins and it could maintain the reflectivity over a three-month experimental campaign. The other is a cover window just in front of the reflector. Candidates of the window materials were exposed to the LHD plasmas and the degradation of the transmissivity of ZnSe and silicon, which are used for infrared and far infrared laser light, respectively, were small.
[show abstract][hide abstract] ABSTRACT: Electron density measurement remains indispensable to control fueling on
a DEMO reactor. For steady-state operation of the DEMO reactor, density
measurement should be highly reliable and accurate. A dispersion
interferometer and a Faraday polarimeter are free from measurement
errors caused by mechanical vibrations. Hence combination of the two
diagnostics yields a suitable system for density measurement on future
steady-state fusion reactors. A wavelength around 1 µm is one of
the desirable candidates in terms of the fringe shift and the Faraday
rotation angle, the variety of optical components, and the efficiency of
frequency doubling for the dispersion interferometer. This paper
presents a conceptual design for the dispersion interferometer and
Faraday polarimeter with a 1 µm light source.
[show abstract][hide abstract] ABSTRACT: An yttrium-aluminium-garnet (YAG) Thomson scattering (TS) system was constructed and applied to the tandem mirror GAMMA 10 device to measure the electron temperature and density. A large solid-angle TS light-collection system was achieved by use of a spherical mirror system and large numerical aperture of bundled optical fiber. A five-channel polychromator with avalanche silicon photo diodes was used. Calibration experiments for TS optical system were performed by Rayleigh and Raman scatterings. An electron temperature increases from 0.04 keV to 0.09 keV was observed with application of electron cyclotron heating (ECH) in the plug/barrier (P/B-) cells. We successfully obtained the radial electron temperature profiles without and with P/B-ECH.
Journal of Instrumentation 01/2012; 7(03). · 1.66 Impact Factor