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  • American Institute of Physics (AIP)  (41)
  • National Academy of Sciences  (8)
  • 1
    Electronic Resource
    Electronic Resource
    The role of small-impact-parameter electron-loss processes on ion temperatures measured by active-beam plasma diagnostics (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 57-63 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The shape of the energy distribution of scattered particles in an active-beam scattering experiment can be influenced considerably by the presence of highly charged impurity ions in the plasma. In this work it is shown theoretically that multiply charged impurities have only a small effect on the scattering distribution at low energies (〈10 keV/amu) and at high energies (〉75 keV/amu). The effect of the impurities is the most pronounced for energies close to 50 keV/amu. The results of the calculations are in good agreement with experimental results at various energies. Extrapolation to higher beam energies leads to the conclusion that the active-beam scattering diagnostics can be applied also in future fusion devices for measuring the local ion temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343375
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  • 2
    Electronic Resource
    Electronic Resource
    On the spatial and temporal resolution of ion temperature measurements based on neutral beam scattering: Comment on "Design of an ion temperature diagnostic based on neutral beam scattering'' [Rev. Sci. Instrum. 57, 1792 (1986)] (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1320-1321 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Small-angle neutral beam scattering is a promising technique to measure the local ion temperature in a hot plasma. We will show that in general a 10% accuracy in the temperature measurement can be obtained with a temporal resolution in the order of 1 ms and a spatial resolution of 10 cm. These values are less favorable than previous claims by Van Heesch et al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139412
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  • 3
    Electronic Resource
    Electronic Resource
    Fast pulsed radar reflectometry for the Textor Tokamak : 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. 1034-1037 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Progress in fusion research shows an increasing demand for diagnostics with high temporal and spatial resolution in order to study small and fast phenomena in fusion plasmas. Therefore, a new ten-channel pulsed radar reflectometer is under development for the TEXTOR Tokamak, to measure electron density profiles in the range of 0.4–4×1019 m−3 at a high repetition rate of 2 MHz. An additional feature of this diagnostic is the possibility to perform correlation measurements at 10 MHz repetition rate to investigate density fluctuations. The reflectometer will scan the plasma with 1-ns-long radar pulses in the 18–57 GHz range. In spite of the long flight time of the pulses of about 100 ns, the above mentioned high repetition rates could be achieved by time multiplexing the generation and reception of the radar pulses. Temporal selection of the received pulses is performed by fast switching of the local oscillators inputs of the heterodyne receiver, to generate time windows in which the reception of the reflected pulses is expected. An embedded VME controller will manage the system and store the data with a speed of 20 Msamples/s, up to a maximum of 64 Mbyte data per plasma shot. In order to facilitate the handling of such a huge amount of data, an advanced data reduction scheme is being developed. Remote operation with a fast data link from FZ Jülich (Germany) to FOM Nieuwegein (The Netherlands) will be possible. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149426
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of ion temperatures by means of Rutherford scattering of energetic neutrals above the limiting angle (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 468-473 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique to measure the ion temperature in a thermonuclear plasma is proposed, based on Rutherford scattering of a beam of energetic neutral particles by the plasma ions. If the mass of the beam particles, mb, is larger than the mass of the scattering ions, mp, a sharp maximum (limiting) angle θlim=sin−1(mp/mb) exists in case the thermal velocities of the plasma ions are neglected. When the scattering ions have thermal velocities, however, scattering of beam particles can occur through angles larger than θlim. Measurement of the intensity of particles above the limiting angle can be used to find the temperature of the plasma ions, with a 10% accuracy and a spatial and temporal resolution of 10 cm and a few μs, respectively, provided the ion velocity distribution is Maxwellian. A feasibility study elucidates that this method can also be used to measure the temperature of a 3He minority component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343128
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  • 5
    Electronic Resource
    Electronic Resource
    Steady state off-axis sawtoothing in the Rijnhuizen Tokamak project (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3898-3905 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A family of off-axis, or annular, instabilities has been studied using Thomson scattering, soft X-ray emission, and two electron cyclotron emission diagnostic systems. In the Rijnhuizen tokamak (RTP) [N. J. Lopes Cardozo et al., Plasma Physics and Controlled Nuclear Fusion Research 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 1, p. 271] these phenomena are invoked in a controlled way in discharges with specific (off-axis) deposition of electron cyclotron heating (ECH) and persist during most of the heating period, or during many current diffusion times. Based on coherent mode analysis at the crash time, the instabilities are associated with resonant surfaces near simple rational values of q (〈fraction SHAPE="CASE"〉32, 2, and 3). A parameter study shows an increase of reheat rate and a decrease of sawtooth period with increasing ECH power and — in contrast to observations in other experiments — with increASING density as well. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873652
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  • 6
    Electronic Resource
    Electronic Resource
    A high resolution multiposition Thomson scattering system for the Rijnhuizen Tokamak Project (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3380-3392 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high resolution multiposition Thomson scattering setup to measure the electron temperature (Te) and density (ne) of a hot plasma is described. The system is operational at the Rijnhuizen Tokamak Project. Light from a high power pulsed ruby laser is scattered by the free plasma electrons and relayed to a Littrow polychromator for spectral analysis. The spectrally and spatially resolved light is detected by a GaAsP photocathode. The two-dimensional image is intensified and recorded with a charge-coupled device camera.Te in the range of 50 eV–6 keV can be measured at 115 spatial elements of 2.6 mm length along the laser beam. The observation error is 〈6% at ne=2×1019 m−3 and smaller for higher ne. The high resolution and accuracy enabled the observation of small scale structures in Te and ne. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148345
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  • 7
    Electronic Resource
    Electronic Resource
    The electron cyclotron absorption diagnostic at the Rijnhuizen tokamak project (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4439-4447 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new 20-channel electron cyclotron absorption diagnostic has been developed at the Rijnhuizen tokamak project. It is the first time the electron pressure profile in a tokamak plasma can be measured directly with a time resolution of 1 ms. The diagnostic measures simultaneously the emission and absorption of the second harmonic electron cyclotron frequencies. Microwaves are injected from the high field side and detected at the low field side in the equatorial midplane. The transmitted power is measured after a single pass through the plasma column. The absorption measurements are complicated by nonresonant losses: refraction of the injected microwaves (losses up to 100%), and scattering of microwaves by density fluctuations (losses 2%–3%). A fast algorithm has been developed to obtain a quantitative measure for these nonresonant losses. This calculation method is based on a parametrization of the experimental data. Combining the electron cyclotron absorption (ECA) measurements and the parametrization provides a reliable tool for determining the optical depth, the electron temperature, and the electron pressure. A good agreement was found between pressure and temperature profiles, measured with ECA and other diagnostics. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148411
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of mode scrambling on pulsed radar reflectometry applied to high shear devices : 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. 473-476 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article the effect of mode scrambling on the operation of pulsed radar reflectometers working in the ordinary polarization mode on devices with a high magnetic shear is studied. Mode scrambling occurs when the magnetic field changes considerably on length and/or time scales which are similar to or smaller than those of the probing wave. In this case the polarization of the mode is not conserved during passage through the plasma, and power is transferred from ordinary to extraordinary mode and vice versa. Calculations with a full-wave code are performed for two different high-shear devices: the RFX reversed field pinch and the LHD torsatron. The conclusion of the work is that the density profiles in these devices can excellently be measured by a pulsed radar reflectometer operating in the ordinary mode. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147609
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  • 9
    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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  • 10
    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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