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内容記述 |
A new bolometer system using an infrared (IR) camera has been developed to measure the 3-D structure of plasma radiation. This bolometer is called the IR imaging bolometer (IRIB) and of this diagnostic there are two types of the mask pattern that are known as the Segmented Mask Infrared Imaging Bolometer (SIB) and the Infrared Imagine Video Bolometer (IRVB). The incident radiation power coming from the plasma is collimated by an aperture and then absorbed by a thin foil located in the vacuum vessel. An IR camera outside of the vacuum vessel measures the temperature rise of the foil by means of the thermal radiation that passes through the vacuum interface by means of an IR vacuum window. Therefore, this system does not use electrical vacuum feed-throughts, and has a very simple design as described above, compared to conventional resistive bolometers. The difference between the two IR bolometer systems is in how the spatial channels are determined. The spatial channels of the SIB foil are physically defined and separated by the segmnented mask and those of the IRVB are determined by numerically dividing up the space on a single large foil exposed to the plasma radiation.<br /> In this study, the design, production and installation of the two differential types of IRIB systems were made for LHD.<br /> The mask was designed by taking into consideration the incident power of the radiation. For a sufficient signal-to-noise ratio of the detected foil temperature, a thin metal foil was used in the mask, aluminum with a thickness of aobut 0.8μm for the SIB system and gold with a thickness of about 1μm for the IRVB system were selected. The other parts of these systems including the aperture plate, the light shielding pipe and the support of the IR camera were also designed.<br /> After the installation of these IR bolometers, an in-situ calibraiton experiment was done. The common parameters for both systems, the calibration factor (K/mW) and the cooling decay times, were measured using a He-Ne laser as a known radiation source. For the SIB system, the calibration was done for each channel and for the IRVB system, a combination of in-situ calibraiton and model profile of the temperature rise of the foil was used.<br /> Using these coefficients, the plasma radiation power density at the foil was calculated from the two-dimensional temperature distribution of the foil as measured by the IR camera. This resulted in images of the plasma radiation intensity with a sufficient signal and a time response to demonstrate the usefulness of this two-dimensional diagnostic system for plasma radiation.<br /> The merits of the IR bolometer are as follows:<br /> 1. Broad two-dimensional radiation brightness profiles are measured by one IR camera using infrared camera imaging technology.<br /> 2. Electrical vacuum feed-throughs are not necessary in this system as the information aobut the foil temperature is passed as IR radiation through an IR vacuum window to the IR camera.<br /> 3. One IR bolometer has over one hundred spatial channels.<br /> 4. For the case of the IRVB, these spatial channels can be determined after the plasma experiments with flexibility depending on the experimental objectives and the conditions of the plasma.<br /> In the latter half of this thesis, some experimental results are shown using the IRVB data. At present two IRVBs are installed, one at an upper port and the other at a tangential port, and began to measure the plasma radiation from two directions simultaneously during the 2001-2002 experimental campaign in LHD. Both of these IRVB biew the same field period and use a 1μm thick gold foil. The frame rates of these IR cameras are 15Hz for that with the tangential views and 60Hz for that with the view from the upper port.<br /> Initial measurements with the IRVB at the tangential port show the variations of the radiative structure as two-dimensional brightness profiles and are compared to data from resistive bolometer arrays, the visible CCD camera and the magnetic field line simulation. Images from two different limiter experiments show the source of the radiation to be localized near the plasma-limiting surface. Also comparison with the magnetic field line calculation shows the structure of a hollow radiation profile in the helical geometry of LHD during standard discharges using the natural helical divertor. In particular, a change in the radiation structure was observed as a continuous series of images or movie made by the IRVB as the discharge passes through assymetric radiative collapse.<br /> Finally, using data from the two IRVBs, the three-dimensional position of the radiation source in the field of view of the two cameras was determined during the collapse. The brightness source region of the inboard asymmetric collapse was observed to be below the horizontal midplane at the vertically elongated cross-section of the plasma and this region continued in an axisymmetric manner in the field of view of the two cameras (approximately half of a field period). This was confirmed by qualitative agreement of the measured images with a calculation of the two-dimensional brightness profiles at each camera resulting from an axisymmetric model of the radiation source localized at the lower inboard side of the torus. |
要旨・審査要旨 / Abstract, Screening Result (384.9 kB)
