{"created":"2023-06-20T13:22:51.925305+00:00","id":3574,"links":{},"metadata":{"_buckets":{"deposit":"f68ac3c0-e96e-4a0f-8976-c2c6e6361e02"},"_deposit":{"created_by":21,"id":"3574","owners":[21],"pid":{"revision_id":0,"type":"depid","value":"3574"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00003574","sets":["2:427:12"]},"author_link":["1419","1420","1418"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"明, 廷〓"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ミン, ティンフン"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2012-09-28"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（学術）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"In order to achieve economical fusion reactors, a high beta operation of the plasma\r\nis required. When the plasma beta, i.e. the plasma pressure divided by the magnetic\r\npressure, increases, the induced pressure gradient drives MHD instabilities.\r\nTherefore, the understanding of the MHD instabilities is one of the key issues to\r\nrealize high beta plasmas. The spatial structure of the instabilities is essential\r\nin understanding of their characteristics. Computed tomographic reconstruction\r\n(CTR) using the soft X-ray emission is one of the standard techniques for that\r\npurpose. In the Large Helical Device (LHD), the arrangement of the detectors\r\nsuitable for the CTR is difficult; due to the superconducting coil systems, it is\r\nnot possible to arrange the detectors in a way that the plasma is observed from\r\ndifferent directions. The tangentially viewing imaging system has been thus used\r\nfor the observation of the core MHD activities. And such tangentially viewing\r\nimaging systems have been also developed on many devices around the world.\r\nHowever, those imaging systems are using soft X-ray emission, which are good\r\nfor observations of the core plasma activities but not good for studies of the edge\r\nplasma activities. A newly developed high-speed imaging system using vacuum\r\nultraviolet (VUV) emission from the edge LHD plasma is presented in this study.\r\nThe VUV imaging system is composed of a telescope made of Mo/Si multilayer\r\nmirrors, micro-channel plate (MCP) and a high-speed visible CMOS camera.\r\nWith Mo/Si mirrors, VUV photons with a wavelength of 13.5 nm can be\r\nselectively measured. A telescope optics rather than pin-hole optical system is\r\nselected; the solid angle of the mirror viewed from the plasma is much larger than\r\nthe solid angle of a pinhole system. Therefore, faster optics, suitable for fluctuation\r\nstudy can be constructed. A Zr filter is installed to cut-off the low energy\r\nVUV photons which can also be reflected by the Mo/Si mirrors. The image is\r\nthen detected by MCP and recorded by the high-speed camera. By measuring\r\nthe CVI line emission around 13:5nm, edge MHD activities are directly visualized\r\nby this device. Additionally, since the time evolution of line emission of C VI is\r\nselectively measured, it is possible to carry out carbon impurity transport study\r\nwith this imaging system.\r\nData analysis methods for the imaging data have been developed in this thesis.\r\nSince the imaging data are line-integrated ones, tomographic reconstruction\r\nof local emission profile from the line-integrated data are required. Construction\r\nof the so-called geometry matrix by which the local emission is related with lineintegrated\r\nimage is discussed. If an arbitrary three-dimensional emission profile\r\nis assumed, reconstruction from a two-dimensional image is not possible. An\r\nassumption that the emission along the magnetic field line is constant is made.\r\nThereby a new method is developed to construct the geometry matrix. In this\r\nmethod, sight lines are projected to curved sight lines on a cross-section (horizontally\r\nelongated section in this thesis). The line elements in a sight line are\r\nconnected to the line elements in the curved sight line along the magnetic field\r\nlines. Then the CTR problem for tangentially viewing case is reduced to a standard\r\n2D tomography problem with peculiar sight lines. HINT2 equilibrium code\r\nis used to estimate the magnetic field lines. With HINT2 code, magnetic field\r\nline traces can be made with finite beta condition. Magnetic field lines outside\r\nthe last closed magnetic surface (LCFS) can be also estimated. This is good for\r\nthe VUV imaging diagnostics since it is possible that C VI emission may come\r\nfrom the stochastic region which is outside the LCFS. After the construction of\r\ngeometry matrix, synthetic images can be calculated according to the relation of\r\nline-integrated image and local emission profile.\r\nThe performance of the tomographic reconstruction method is investigated\r\nin LHD configuration. Several algorithms have been tested, such as Phillips-\r\nTikhonov (PT) method, maximum entropy method (MEM), truncated singular\r\nvalue decomposition (TSVD). According to the phantom test results, PT gives\r\nthe best performance, and the spatial mode structure with high mode number\r\n(m ～ 10) has been shown to be reconstructed even with a complex LHD con\r\nfiguration. The noise level where the reconstruction is available is investigated.\r\nThe maximum noise level is about 6%. The quality of the reconstruction results\r\nis however more sensitive to the accuracy of the equilibrium magnetic field.\r\nA simple transport model has been constructed to study the behavior of the\r\ncarbon impurity. In this modeling, transport process, ionization and recombination\r\nprocess are included. With this transport model, time evolutions of the C VI\r\nemissivity are estimated assuming a transport coe\u000ecient profile. It is confirmed\r\nthat the CVI emission is peaked in the edge region of LHD plasma in normal\r\nexperimental condition.\r\nUsing this model, the penetration depth of injected carbon pellets is estimated\r\nfrom the imaging data. The ionization process is dominant just after the\r\npellet ablation. Therefore, the image just after the deposition is used to study\r\nthe initial deposition profile. The estimated penetration depth is qualitatively\r\nconsistent with the estimation made by the pulse width of the Hα emission signal\r\nthat is caused by the carbon pellet injection.\r\nMHD activities with low-frequency (about 0:75kHz) have been successfully\r\nmeasured by the VUV imaging system. The amplitude of the MHD activities is\r\nfairly large and degradation of the con\fnement is observed with this MHD modes.\r\nThe poloidal mode number (m = 1) and the location of the mode (r=a ～ 0:9)\r\nis estimated. The 2D spatial structure of the m=n = 1=1 mode has been identi\r\nfied by comparing the synthetic images assuming and images measured experimentally.\r\nThe estimate of the mode number is consistent with that estimated\r\naccording to the magnetic probe signal and the location is consistent with q =1\r\nrational surface.\r\nThe proof of concept, this type of imaging system can detect fuctuations\r\nlocalized in the edge region, is shown successfully. Although the maximum sampling\r\nrate of this device is as low as 2kHz at the present moment, it is limited\r\nonly by the intensity of the plasma emission. And the data analysing technique\r\ndeveloped in this study is shown to be quite useful in analysing the MHD activities.\r\n7.2 Outlook\r\nThe challenge is to improve the framing rate up to ～ 10kHz to realize the concept\r\nthat the VUV imaging system is suitable for investigating normal edge MHD\r\ninstabilities in LHD. For normal discharges, the carbon impurity concentration is\r\nalmost stable and very low, upgrade of the optical system is required to improve\r\nthe framing rate. Since the total number collected by the imaging system is\r\nproportional to the imaging area of the mirrors, a new mirror system, which has\r\nlarger imaging area, is under plan.\r\nAdditionally, the carbon pellet injection is widely applied to obtain high\r\ntemperature plasma in LHD. And MHD activities have been observed during the\r\npellet injection. Since the concentration of the carbon impurity is much higher\r\nthan that in normal discharges, hence, the intensity of the C VI emission can be\r\nsignificantly increased in such discharges. Therefore, it is possible to study such\r\npellet induced MHD phenomena with this imaging system.\r\nThere are many applications of this technique. Verification of the MHD\r\nmodel related with the resonant magnetic \feld penetration is an important example\r\nand will be investigated in future. And the tomographic reconstruction\r\nwill be tried to obtain the 2D emission profile, which enables to investigate the\r\nphenomena where asymmetric distribution exists.\r\nAnd the important topics to be studied using refined VUV telescope system\r\nare as follows:\r\n(1) Locked mode.\r\nIt has been observed that the edge MHD instabilities slowed down and\r\nstopped. A large magnetic island is formed after the locking; the performance of\r\nthe plasma degraded significantly by the mode locking. The detailed mechanism\r\nthat how the rotating mode locks and how to expand to be a static island will\r\nbe studied.\r\n(2) ELM-like activities and the relation of RMP field\r\nIn H-mode plasma in LHD, edge MHD instabilities drive ELM-like relaxation\r\nevents. The detailed process of the ELM-like collapse will be studied. When the\r\nRMP (LID) field is applied, the scale of the ELM is reduced. The spatial structure\r\nof the ELM activities with RMP field will be estimated.\r\n(3) Core density collapse event\r\nIn the core density collapse events observed in the high-density plasma experiments,\r\nthe ballooning mode might play an important role. One of the advantage\r\nof the imaging diagnostics is that mode structure with high mode number can be\r\nmeasured directory. The pre-cursor oscillations caused by the ballooning mode\r\nwill be studied.\r\n(4) Physics of Island formation\r\nWhen the externally applied field is shielded, there is no magnetic island\r\ninside the plasma. When the magnetic field penetrates, the magnetic island is\r\nformed. The VUV telescope can monitor the formation process of the island with\r\nhigh framing rate. The comparison of the model of the island can be performed\r\nby the comparison of the time scale of the expansion of the magnetic island.\r\nThis kind of fast measurement can be realized two dimensionally only by VUV\r\ntelescope system at present in LHD.","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第1544号 ","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"物理科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"10 核融合科学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2012"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"MING, Tingfeng","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲1544_要旨.pdf","filesize":[{"value":"410.5 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨","url":"https://ir.soken.ac.jp/record/3574/files/甲1544_要旨.pdf"},"version_id":"473fda8c-b48f-4430-aede-56e9361475f9"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Development of high-speed vacuum ultraviolet imaging camera system for high-temperature plasma diagnostics","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Development of high-speed vacuum ultraviolet imaging camera system for high-temperature plasma diagnostics"},{"subitem_title":"Development of high-speed vacuum ultraviolet imaging camera system for high-temperature plasma diagnostics","subitem_title_language":"en"}]},"item_type_id":"1","owner":"21","path":["12"],"pubdate":{"attribute_name":"公開日","attribute_value":"2013-05-24"},"publish_date":"2013-05-24","publish_status":"0","recid":"3574","relation_version_is_last":true,"title":["Development of high-speed vacuum ultraviolet imaging camera system for high-temperature plasma diagnostics"],"weko_creator_id":"21","weko_shared_id":-1},"updated":"2023-06-20T15:29:00.452750+00:00"}