Bench Testing of New Polarimeter with Silicon Photoelastic Modulator for Short Wavelength FIR Laser

A short wavelength laser whose wavelength is about 50 μm is preferable for a polarimeter and an interferometer in large fusion devises. This paper reports the development of a polarimeter with a photoelastic modulator(PEM) for a CH3OD laser (wavelengths of 57.2 and 47.6 μm). The PEM with a high-resistive silicon as a photoelastic element has been newly developed. The transmissivity of the high-resistive silicon is high in a far infrared region. The polarimeter with the Si PEM has been tested and the polarization angle is successfully measured. Noise sources (a multi-reflection of the laser beam in the photoelastic element, a measurement error of amplitude of a detector output and an estimation error of the retardation) of the measured angle are also discussed

Nonstop Lose-Less Data Acquisition and Storing Method for Plasma Motion Images

Plasma diagnostic data analysis often requires the original raw data as they are, in other words, at the same frame rate and resolution of the CCD camera sensor. As a non-interlace VGA camera typically generates over 70 MB/s video stream, usual frame grabber cards apply the lossy compression encoder, such as mpeg-1/-2 or mpeg-4, to drastically lessen the bit rate. In this study, a new approach, which makes it possible to acquire and store such the wideband video stream without any quality reduction, has been successfully achieved. Simultaneously, the real-time video streaming is even possible at the original frame rate. For minimising the exclusive access time in every data storing, it has adopted the directory structure to hold every frame files separately, instead of one long consecutive file. The popular ‘zip’ archive method improves the portability of data files, however, the JPEG-LS image compression is applied inside by replacing its intrinsic deflate/inflate algorithm that has less performances for image data

Advanced Laser Diagnostics for Electron Density Measurements

This paper describes innovative laser diagnostics under development at the National Institute for Fusion Science, aiming for the establishment of reliable density measurement techniques in the next step magneticallyconfined fusion devices. There are two approaches, interferometry and polarimetry. A new type of two color laser (47.6/57.2-μm CH3OD) interferometer has been developed and its original function, vibration subtraction,was confirmed in a test stand. The line integrated density measurement at Compact Helical System by using the polarimeter based on Cotton-Mouton effect was demonstrated by the use of a 337-μm HCN laser source

Improvements of CO2 Laser Heterodyne Imaging Interferometer for Electron Density Profile Measurements on LHD

After installation of CO2 laser (wavelength 10.6 μm) heterodyne imaging interferometer (CO2 HI) in 2001, continuous developments have been carried out to improve the measurements capability and stability of operation. The CO2 HI works almost without phase jumping at high electron density (> 1 × 1020 m-3), where the existing far infrared laser (wavelength 118.9 μm) interferometer suffers from fringe jump due to the reduction of signal intensity caused by refraction. However a second interferometer is required to compensate mechanical vibration. A YAG laser (wavelength 1.06 μm) heterodyne imaging interferometer (YAG HI) is presently used for the vibration compensation. In the 10th LHD experimental campaign (2006?2007), sixty four channels of CO2 HI to measure electron density profile and ten channels of YAG HI to measure mechanical vibration are working. A measurement example of a pellet fuelled high-density discharge is reported

Adaptive data migration scheme with facilitator database and multi-tier distributed storage in LHD

Recent “data explosion” induces the demand for high flexibility of storage extension and data migration. The data amount of LHD plasma diagnostics has grown 4.6 times bigger than that of three years before. Frequent migration or replication between plenty of distributed storage becomes mandatory, and thus increases the human operational costs. To reduce them computationally, a new adaptive migration scheme has been developed on LHD’s multi-tier distributed storage. So-called the HSM (Hierarchical Storage Management) software usually adopts a low-level cache mechanism or simple watermarks for triggering the data stage-in and out between two storage devices. However, the new scheme can deal with a number of distributed storage by the facilitator database that manages the whole data locations with their access histories and retrieval priorities. Not only the inter-tier migration but also the intra-tier replication and moving are even manageable so that it can be a big help in extending or replacing storage equipment. The access history of each data object is also utilized to optimize the volume size of fast and costly RAID, in addition to a normal cache effect for frequently retrieved data. The new scheme has been verified its effectiveness so that LHD multi-tier distributed storage and other next-generation experiments can obtain such the flexible expandability

Observation of charge-exchange spectra on C6+ +H in low-energy collision

The extreme ultraviolet spectra of C VI have been studied for a Neutral Beam Injection (NBI) plasmas in Large Helical Device (LHD). A strong distortion in the population distribution over the excited levels was observed and we conclude that is caused by charge-exchange recombining (CXR) processes between C^6+ ion and recycling neutral hydrogen. Spatially resolved measurements show that the C^6+-H CXR processes take place in the plasma peripheral region in LHD. We have taken a CXR pan of C VI 1s-4p line using the result of a calculation code

Conceptual Design of Electron Density Measurement System for DEMO-Relevant Helical Plasmas

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 ?m 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 ?m light source

Broadband Multichannel Radiometer for ECE Measurements on KSTAR

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 (110-162 GHz and 164-196 GHz) can cover a frequency range of 110-196 GHz. 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 1 ?s is about 0.23 eV. 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