K. Narihara

M. Inomoto

S. Ito

T. Nonaka

T. Yamada

Y. "Ono

Y." Nagayama

National Institute for Fusion Science (NIFS-Repository)

Study on Quick Similarity Search in Massive-size Waveform Databases Hochin, T., Nomiya, H. (Kyoto Inst. of Tech.) Okumura, H. (Mie Univ.) Nakanishi, H., Kojima, M., Nagayama, Y., Ohdachi, S., Emoto, M., Ohsuna, M. Experiments of the fusion phenomena produce a lot of sequences of time-varying values which form waveforms. If the waveforms similar to a desired one can be obtained by using computer system, the burden of researchers in searching similar waveforms will extremely be decreased. We have addressed to the issue on this kind of retrieval. 1) We have proposed an indexing method of the severely and quickly changing plasma waveforms for accelerating search and retrieval of their subsequences. 2)The method divides a waveform into fine-grained segments. The similar segments are grouped into a segment group, which is managed by using a multi-dimensional index. A sequence of segments is used as a unit in matching subsequences in the retrieval. This method could bring us the quick construction and the small size of the index, and the good performance and the good retrieval correctness. 2)This paper treats movies of plasma discharge, which are called plasma movies. Although a plasma movie is a kind of time series data, it could not be treated well through the conventional methods of handling time series data because a unit of a movie is a picture (frame).  A plasma movie is divided into segments as in the method described above. 2) A segment includes sixteen frames. The duration of a segment is about 0.5 second. The frame is of the center region of the original frame for the purpose of excluding the character strings of shot number, and so on. The width and the height of a frame are 256 pixels and 128 pixels, respectively. Feature values described later are obtained from each segment. By using the feature values, dissimilarity of the key segment of a plasma movie and a segment of a plasma movie stored in a database is calculated. The absolute values of the Fourier coefficients obtained by applying three-dimensional Fourier transformation to the luminance values of a segment are used as the feature values. Ten coefficients are selected because many coefficients are obtained. We have tried three methods for this selection. The first method uses variances of the absolute values of the Fourier coefficients obtained from 82 segments out of five typical plasma movies. Ten coefficients, which have the largest variances, are selected. The second method uses the coefficient of variation, which is the standard deviation divided by the average value, of the absolute values of the Fourier coefficients. The last method filters the coefficients by using their variances, then select ten coefficients whose coefficients of variation are the largest. Correctness of retrieval is evaluated by using ten plasma movies (totally 120 segments). A snapshot of the key segment, which is the third segment of the plasma movie whose shot number is 40215, is shown in Fig. 1. It is evaluated with recall (= ncor / nsel) and precision (= ncor /ncorall), where ncor is the number of the correct segments retrieved, nsel is the number of the segments retrieved, and ncorall is the total number of the correct segments. The correct segments are manually decided from 120 segments. The number of the correct segments is 14. The recall-precision curves are shown in Fig. 2. In Fig. 2, the method using the Fourier coefficients selected by using the variance (coefficients of variation, respectively) is depicted by “Variance” (“COV”). The method using the Fourier coefficients selected by using the coefficients of variation after the filtering with variances is depicted by “Two steps.” In the “COV” method, the first two candidates are correct, while the followings include errors. The “variance” method retrieves many errors in the first several candidates. The first several candidates are not correct in the “two steps” method, while the latter ones are correct. This brings the good accuracy to this method. The retrieval key segment varies from dark to bright, while the incorrect segments retrieved as the first several candidates vary from bright to dark. This may be caused by the fact that the phase difference is not considered in the feature values, which are the absolute values of the Fourier coefficients.Fig. 1.  A snapshot of the key segment. 㪇㪅㪇㪇㪅㪉㪇㪅㪋㪇㪅㪍㪇㪅㪏㪈㪅㪇㪇㪅㪇 㪇㪅㪉 㪇㪅㪋 㪇㪅㪍 㪇㪅㪏 㪈㪅㪇㪩㪼㪺㪸㫃㫃㪧㫉㪼㪺㫀㫊㫀㫆㫅 㪫㫎㫆㩷㫊㫋㪼㫇㫊㪭㪸㫉㫀㪸㫅㪺㪼㪚㪦㪭Fig. 2. Evaluation result of retrieval accuracy. 1) Hochin, T., Koyama, K., Nakanishi, H., Kojima, M., LABCOM group: Extension of frequency-based dissimilarity for retrieving similar plasma waveforms, Fusion Eng. Des. 83 (2008) 417-420 2) Yamauchi, Y., Hochin, T., Nomiya, H., Nakanishi, H., Kojima, M.: Fast Partial Similarity Retrieval Method of Swinging Time Series, IPSJ SIGDBS 2009-DBS-148 (17) (2009) 1-8 (in Japanese)   Fig. 1 The laser beam path and measuring points for thepresent 3x3 2-D Thomson scattering measurement in thepoloidal flux contour of ST plasma (top), the measured 2-Dcontour of electron temperature (middle) and the Thomsonscattered lights as a function of wavelength for Gaussianfitting (bottom).  Fig. 2 Measurement points for the proposed 2-D Thomsonscattering measurement (top) and r-z profile of themeasured electron temperature (bottom) Development of Two Dimensional Thomson Scattering Measurement System   Ono, Y., Nonaka T., Ito, S., Yamada, T., Inomoto, M. (Univ. Tokyo, Dept. Advanced Energy), Narihara, K., and Nagayama Y. (NIFS)  The Thomson scattering method is the most reliable diagnostics for electron temperature measurement and its two dimensional (2-D) measurement is expected to solve magnetic reconnection in TS-4 experiment and electron transport in LHD experiment. We have developed a new cost-effective 2-D Thomson scattering measurement system using multi-reflection of a single laser light and its time-of-flight effect. A new characteristics for our system are as follows: (1) multiple reflections of laser light to cover m x n (2-D) measuring points on r-z plane, (2) usage of time-of–flight of laser light to save the number of polychromators and detectors, and (3) flexible usage of laser path length to control the delay times of scattering signals from those measuring points. They enable us to develop a low-cost 2-D Thomson scattering system using a single Laser and polychromators equivalent to the 1-D system, because the scattering lights from n measurement points are measured by a single polychromator.     In 2009, we optimized the 2-D (3x3) measurement system and measured for the first time the 3x3 Thomson scattered signals using three polychromator, collecting lens system and optical fiber system. Its laser beam was reflected three times by the mirror to cover the center area of out TS-4 spherical tomamak (ST) plasma. The Thomson scattering signals from the 3x3 measuring points were successfully measured by those collecting optics and polychromator system. Figure 1 shows the three Thomson scattering signals measured with equal time intervals of 30nsec corresponding to laser flight length of 12m. Figure 2(bottom) shows the time evolutions of Thomson scattering signals at three radial positions: r=360mm, 540mm and 620mm. The time axis indicates the axial position because of the time-of-flight measurement. Those signals are used to calculate the electron temperature by Gaussian fitting. Finally, 2-D contour of electron temperature were obtained as shown in Fig. 2(bottom). This successful result supports the validity of our 2-D Thomson scattering method by multiple reflection and time-of-flight of laser. The remaining problem is 1) suppression of plasma light and 2) improvement of laser beam quality along the long laser beam path. Under the present experimental condition, we will check the upper limit of reflection number of laser beam.   1) S. Ito ， T. Sumikawa ， E. Kawamori ， Y. Ono, “Development of Multipoint Thomson Scattering Measurement System Using Multiple Reflections and Time-of-Flight of Laser Light, IEEJ Trans. Fun. Mat. 128-A, (2008), p.499. 2) Y. Ono et al., “Ion and Electron Heating Characteristics of Magnetic Reconnection in TS-3 and UTST Merging Startup Experiments”, Fusion Energy 2008, EX/P9-4, 2008. 185§36. Dev lopment of Two Dime sional Thomson Scattering Measurement SystemOno, Y., Nonaka, T., Ito, S., Yamada, T., Inomoto, M. (Univ. Tokyo, Dept. Advanced Energy), Narihara, K., Nagayama, Y.

Development of Two Dimensional Thomson Scattering Measurement System

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Development of Two Dimensional Thomson Scattering Measurement System

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