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  • 11
    Electronic Resource
    Electronic Resource
    Photon recycling system for multiposition tangential Thomson scattering : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 501-503 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Multiposition tangential Thomson scattering makes it possible to measure the profiles of the local drift velocity and current density of a tokamak plasma. To achieve a reasonably small observational error (20%) a high photon yield is required. In this paper we propose an optical system to increase the photon yield by about a factor of 7. Photons from a pulsed ruby laser are captured in a ring cavity by means of an electro-optical switch. The trapped laser beam recirculates about 14 times through the sampling volume which is part of the cavity, increasing the laser energy of 25 J to an effective energy of about 140 J. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146330
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  • 12
    Electronic Resource
    Electronic Resource
    A new approach to internal disruption analysis with the five-camera soft-x-ray diagnostic on RTP : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 537-539 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel method is presented to analyze internal disruptions (sawteeth), observed with the five-camera soft-x-ray diagnostic at the Rijnhuizen Tokamak Project (RTP). Using four or five cameras, tomographic images with seven poloidal harmonics have been obtained throughout sawtooth crashes and precursor oscillations. The detection of cross-field transport and magnetic reconnection from the reconstructed tomographic images is complicated by the fact that (except during the final phase of the collapse) the time dependence is dominated by the m=1 ideal MHD displacement of the hot core in combination with plasma rotation. It is possible to define quantities, e.g., the plasma volume where the emissivity is within a certain range, whose change is only determined by cross-field transport or reconnection, and are not affected by displacement and rotation. The good spatial resolution of the 80-channel system enables us to compute these quantities with such an accuracy that their sensitivity to plasma rotation and MHD convection is small. Using this approach we find in the sawteeth studied so far that m=1 magnetic reconnection may take place, but affects less than half of the magnetic flux within the q=1 surface, thus ruling out complete reconnection as a mechanism for the final collapse of the hot core in these cases. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146344
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  • 13
    Electronic Resource
    Electronic Resource
    First tomographic reconstructions and a study of interference filters for visible-light tomography on RTP : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 622-624 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An 80-channel visible-light tomography diagnostic is operational on the Rijnhuizen Tokamak Project. This diagnostic uses optical imaging systems from five directions in one poloidal plane to view emission by the plasma. For the application of tomography algorithms, measurements need to be preprocessed to take into account the properties of the imaging system. These properties have been measured and a consistent treatment is demonstrated. An example of a tomographic inversion of a glow-discharge plasma is given. Optical filters can be used to select various wavelength ranges. Because the imaging system gives large angles of incidence on the filter (〈16°), a study has been made to determine the minimum useful bandwidth of interference filters to select spectral lines, which was found to be 5 nm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146541
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  • 14
    Electronic Resource
    Electronic Resource
    Investigation of ion sawtooth activity by Rutherford scattering : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 327-329 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Rutherford scattering diagnostic at TEXTOR has been used to investigate the time evolution of the ion velocity distribution during sawtooth activity. Coherent averaging techniques have been employed to obtain better statistics. The time evolutions of central ion and electron density were found to be strongly correlated in four out of five cases. In one case, where saturation of the sawteeth occurred, a discrepancy between the two has been found, which could be attributed to an influx of impurities towards the end of the sawtooth. Changes of about 20% in the central toroidal rotation of the bulk ions have been found during sawtooth crashes of neutral beam injected discharges, whereas no changes were found in the ohmic case. No statistically reliable statements can be made about changes in the ion temperature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146401
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  • 15
    Electronic Resource
    Electronic Resource
    Heterodyne radiometer at Rijnhuizen Tokamak Project for electron cyclotron emission and absorption measurements : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 416-418 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The 20-channel heterodyne radiometer of the Rijnhuizen Tokamak Project (RTP) measures microwaves in the range between 86 and 146 GHz. The spatial resolution is ∼7–16 mm parallel and 25–1300 mm2 perpendicular to the viewing direction, depending on the position in the torus. A waveguide network gives the opportunity to do alternate measurements of X- and O-mode electron cyclotron emission (ECE) from the low-field side (LFS) and X-mode ECE from the high-field side (HFS). A backward wave oscillator is installed at the HFS, for the purpose of measuring the electron cyclotron absorption (ECA) of the plasma. This set-up also provides a possibility for fast relative calibration of the radiometer. To reduce the effects of multiple-pass reflections and standing waves, Macor viewing dumps are mounted at both sides. A comparison of HFS and LFS ECE measurements during electron cyclotron heating will be given as a first result. First results of ECA measurements were obtained but will be presented in the future. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146486
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  • 16
    Electronic Resource
    Electronic Resource
    Poloidal polarimeter system for current density measurements in ITER : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 726-729 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The polarimeter system for ITER features 10 viewing chords covering almost the full poloidal cross section of the plasma in a fan-like arrangement. The 10 laser beams all enter the plasma via 150 mm diam penetrations through the diagnostic plug at the low-field side. Small retroreflectors at the high-field side mirror the laser beams back towards the penetrations at the low-field side. Extensive feasibility calculations have led to the conclusion that the optimum wavelength for the polarimeter is around 100 μm. At this wavelength counterproductive effects like refraction and electron cyclotron absorption are negligibly small. However, the anticipated Faraday rotation angles are still very large, such that several important plasma parameters can be measured within the requirements set by the ITER team. In this article the status of the conceptual design of the polarimeter system for ITER will be presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149396
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  • 17
    Electronic Resource
    Electronic Resource
    The multichannel triple-laser interferometer/polarimeter system at RTP : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1217-1226 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 19-channel combined interferometer and polarimeter system has recently become operational at the Rijnhuizen Tokamak Project (a=0.164 m, R=0.72 m, Btor≤2.5 T, Ip≤150 kA, plasma pulse duration ≤500 ms), in order to determine the poloidal magnetic field and plasma density distribution simultaneously. The method is based on the separate propagation of two counter-rotating, circularly polarized probing waves, and enables high temporal resolution measurements of both the interferometric and the polarimetric phase change using only one detector per line of sight. In this article a thorough discussion of the (polarization-related) optical, electronic, and computational aspects of the system will be presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147884
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  • 18
    Electronic Resource
    Electronic Resource
    Reflectometry on ITER : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 435-438 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Reflectometry will be used on ITER to measure the density profile in the main plasma and divertor regions, and to measure the plasma position and shape in order to provide a standby reference for the magnetic diagnostics in long pulse discharges. The high temperatures of the ITER core and the resultant significant relativistic downshift of the second-harmonic electron cyclotron absorption imply that both low-field side O-mode and high-field side lower cut-off (X−l mode) systems are required to access the full plasma profile. A low-field side upper cut-off (X−u mode) system will also be required for measurements of the scrape-off layer. For measurements of the plasma position and shape, an O-mode system is optimum due to the large range of magnetic field along the plasma periphery and the wide range of possible plasma configurations achievable on ITER. A robust real-time calibration technique of the whole transmission line is required. It is likely that an accurate estimate of the position of the plasma will require the simultaneous use of signals from the profile reflectometer. For the divertor, profiles with peak densities in the range 1019–1022/m3 are to be measured with a target resolution of 3 mm. The large density range will necessitate the use of more than one system. Installing these reflectometers on ITER incurs additional difficulties such as the routing of the millimetre wave radiation around the complicated first wall and divertor structures and design of antennas able to operate through the first wall and blanket. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148220
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  • 19
    Electronic Resource
    Electronic Resource
    The multichannel triple-laser interferometer/polarimeter system at RTP (abstract) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 446-446 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 19-channel combined interferometer and polarimeter system has recently become operational at the Rijnhuizen Tokamak Project (a=0.164 m, R=0.72 m, Btor≤2.5 T, Ip≤150 kA, plasma pulse duration ≤500 ms), in order to determine the poloidal magnetic field and plasma density distribution simultaneously. The method is based on the separate propagation of two counter-rotating, circularly polarized probing waves, and enables high temporal resolution measurements of both the interferometric and the polarimetric phase change using only one detector per line of sight. In this article a thorough discussion of the (polarization-related) optical, electronic, and computational aspects of the system will be presented.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147602
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  • 20
    Electronic Resource
    Electronic Resource
    Density perturbation studies by means of pulsed radar reflectometry : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 419-421 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A four-channel pulsed radar reflectometry system has been developed for the Rijnhuizen Tokamak Project. The system combines a high spatial and temporal resolution with limited access demands to the tokamak plasma. Steady-state density profiles as measured with the pulsed radar system match very well to the profiles as measured by Thomson scattering and by interferometry. As will be illustrated in this paper, the diagnostic is able to follow fast phenomena as pellet injection and plasma disruptions as well as MHD oscillations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146542
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