{"created":"2023-06-20T13:20:29.278935+00:00","id":509,"links":{},"metadata":{"_buckets":{"deposit":"dad2cd14-abfa-4c42-9c91-7898598634a4"},"_deposit":{"created_by":1,"id":"509","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"509"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00000509","sets":["2:427:12"]},"author_link":["8681","8683","8682"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"中村, 希一郎"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ナカムラ, キイチロウ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2004-03-24"}]},"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（工学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"　Diagnostics of edge plasma parameters are important because plasma properties in the region have key role to determine the global plasma confinement. In particular, transport barriers are of strong interest. Understanding and controlling edge plasmas are also important for the divertor design in fusion reactors. In order to study plasma structure in the area, two-dimensional measurements are essential.<br />　A lithium beam probe (LiBP) is one of the best techniques for the measurement of edge plasma density profile. The LiBP utilizes the emission of the LiI resonance line (2s-2p, 670.8nm)from the injected neutral lithium by electron impact excitation. The LiBP can probe plasmas from the edge to the core crossing the last closed flux surface (LCFS) without perturbation or contamination to the plasma. It has been used in many magnetic confinement devices, but all those measurements are in one dimensional along the fixed beam line. <br />　A LiBP system that can measure two-dimensional plasma structure in the edge plasma region including the separatrix has been designed and installed on CHS. This system has a beam injector with variable injection angle and amulti-channel optical detection system. The beam injector is located on the upside of the torus, which consists of an ion gun with a Li source (6mm diameter)which is thermoionic emission typeβ-eucryptite, a Pierce extractor and cylindrical lens. This section is covered with magnetic shield in order to prevent the effect of CHS stray field. The beam energy is in the range from 10 to 20 keV with an equivalent neutral beam current of about 0.1 mA. The ion beam is neutralized in the Cs neutralizing cell operated at the temperature about 180℃. The beam energy is selected so that it offers both adequate spatial resolution and beam penetration. For the 15 keV beam, the spatial resolution is less than l.7 cm and beam penetration depth is characterized by the 2x10<SUP>18</SUP>m<SUP>-2</SUP> of line-integrated density. The neutral beam diameter is about 20 mm in the CHS vacuum chamber. <br />　Light collection optics, which detects the emission from the LiI resonance line, is located on the side port of the torus. The optical system consists of a lens, optical fibers, optical interference filters and Avalanche photodiode (APD) detectors. Since the angle between beam line and sight line is not at right angle, the observed spectral line suffers Doppler shift. Maximum Doppler shift at beam energy of 15 keV is 0.9 nm. So the optical interference filters are selected with the bandwidth of 2.0 nm. Twenty-five couplers for optical fibers are prepared on the light collection lens corresponding to twenty-five observation points along the beam with about 8 mm spacing. Eight channel optical fibers can select eight observation points by choosing eight couplers among those. The injection beam line angle can be varied between +18ﾟand -18ﾟin the major radius direction. Two-dimensional profile is obtained by changing the beam injection angle shot by shot. Since the signal to noise ratio for the present beam intensity is less than unity (S/N<1), signals from APD detectors are introduced to phase sensitive detectors with 4 kHz beam modulation. Typical time resolution is 10 ms in the present measurements. Taking the related atomic processes into account, the emission profile is converted to the electron density profile.<br />　The CHS is a low-aspect-ratio helical device that has a major radius of 1.0 m and minor radius of 0.2 m. The pole number and the toroidal periodic number of the helical field coils are l=2 and m=8, respectively. The maximum magnetic field strength is 1.8T. Magnetic field configuration can be varied over a wide range by controlling the coil current and its direction. Hydrogen plasmas are produced by electron cyclotron resonance (ECR) heating (170 kW) and additionally heated by the two neutral beam injectors (1.3 MW). The electron density is in the range of 0.5-5x10<SUP>19</SUP>m<SUP>-3</SUP> and typical electron and ion temperatures are l keV and several hundreds of eV, respectively. Low aspect ratio helical device characterizes broken helical symmetry due to strong toroidicity forming ergodic magnetic field line structure outside the LCFS. In CHS, variety of edge magnetic field configuration can be realized by changing the position of the magnetic axis. <br />　Beam emission profiles are obtained both for ECH and NBI heated plasmas of limiter configuration. Electron density is reconstructed from this emission profiles. In this study, multiple atomic processes related with transitions between 2s, 2p and ionized states are taken into account. There are two methods to convert the beam emission profile to the electron density profile. The first one is the beam attenuation method and the second one is the beam intensity method. When the plasma density is large, full emission intensity distribution is measured. Then the density profile can be reconstructed using the beam attenuation method. No calibration is necessary, which is the advantage of this method. The beam intensity method is used when the beam is not fully attenuated within the observation area. The electron density is derived from the beam emission intensity based on the atomic data, sensitivity of the optical system and the beam density. Two-dimensional electron density profiles are derived using those two methods depending on the beam penetration depth.<br />　The experimental data suggests that the ECH plasma is well confined inside the LCFS. Plasmas with density above 10<SUP>18</SUP>m<SUP>-3</SUP> do not exist outside of it. In contrast, the NBI plasma is spreading outside the LCFS toward the separatrix region and noticeable amount of plasma is confined in this ergodic region even though the magnetic field line in the ergodic layer is cut by the vacuum chamber wall (inboard limiter configuration). The plasma with the density of 10<SUP>19</SUP>m<SUP>-3</SUP> exists even 4 cm apart from the LCFS along the equatorial plane. <br />　Edge density profile steeping associated with H-mode like transitions (Edge Transport Barrier)is also observed. The characteristic scale length of the electron density gradient at the LCFS is reduced to 80% of the original one. <br />　Such 2D-diagnostics is expected to play a key role in understanding and the design of helical diverter in future. 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