Similar pattern search for time-sectional oscillation in huge plasma waveform database

Recently there has been drastic data growth in many fusion plasma experiments. Some computer-aided assistance to find similar waveforms has become indispensable for accelerating data recognition and analysis. A similarity search for slowly varying waveforms, which applies “R-tree” index with Java implementation, was already reported [H. Nakanishi, T. Hochin, M. Kojima, LABCOM group, Search and retrieval method of similar plasma waveforms, Fusion Eng. Design 71 (1–4)(2004)189-193]. The next step is the search for time-sectional oscillation patterns. This requires neglecting the initial phase difference between many slices of waveforms. This new algorithm applies power spectrum density (PSD) values instead of FFT complex coefficients. To emphasize the difference between peak PSD frequency of each waveform, its Euclidean distance is multiplied by ωj/ωiωj/ωi (ωj>ωiωj>ωi). By applying “SR-tree” and fast numerical library implemented in C/C++, its computations have been accelerated. This enables the system to deal with much larger data sets. These modifications have successfully extended the application range toward them with verified accuracy.