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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4418-4426 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present various aspects of the calibration of the TFTR lost alpha diagnostic. The diagnostic consists of four detectors, forming a poloidal array at the bottom of TFTR inside the vacuum vessel. The detector is composed of a ZnS(Ag) scintillator and a pair of collimating apertures which permit pitch angle, energy, and time resolution of the escaping flux of high-energy ions (MeV range). The first goal of this study was to establish the absolute calibration of the diagnostic for different particle types and energies. This enables us to compare for the first time, measured losses with loss calculations based on a first-orbit model. However, the factor of 2 uncertainty in the final calibration is still too large for full, quantitative comparisons of the data with the theory based on absolute flux measurements alone. We also present some of the aspects related to the detector's resolution capabilities, its temperature dependence, and its time response.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high spatial resolution CCD based one-dimensional imaging system to measure visible continuum emissivity profiles from Alcator C-Mod tokamak plasmas is described. The instrument has chordal resolution that is better than 1 mm for the edge region of the plasma, where very sharp (1 to 10 mm) gradient lengths in plasma parameters are observed after the formation of the H-mode transport barrier. Each image has up to 2048 pixels, and total spatial coverage goes from 2 cm inside of the magnetic axis to ∼4 cm outside of the last closed flux surface in the ∼22 cm horizontal minor radius plasmas. Time resolution can be varied from 0.21 ms to 4 ms; good signal to noise is achieved with 1 ms integration under typical plasma conditions. The emission over most of the plasma volume is dominated by free–free bremsstrahlung, and can be used to infer local values of the average ion charge (Zeff). Toroidally localized puffing of deuterium, nitrogen, and helium reveals that a significant contribution to the signal in the scrape-off layer at the extreme edge of the plasma can come from diatomic molecular band pseudocontinuum emission. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two new high resolution detectors have been installed on the Alcator C-Mod tokamak to measure the neutral density and ionization rate at the edge of the main chamber plasma. Using a silicon detector sensitive to UV light, and a very narrow filter with transmission peaking at 1216 Å, the Lyman alpha radiation emanating from neutral deuterium (and hydrogen) is measured. The detectors consist of 20 channel arrays which view the plasma tangentially 12.5 cm below the outer midplane, and 10 cm above the inner midplane. The imaging is performed using a 1 mm×3 mm slit, which gives a nominal radial resolution of 2 and 3 mm, respectively. The local emissivity is obtained via a standard Abel inversion technique. Employing well-known branching ratios, and using measured local electron density and temperature, the neutral density and ionization rate are inferred with similar radial resolution. Details of the setup and sensitivity of the results to plasma conditions are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent breakthroughs in silicon detector technology now permit measurement of radiated power over a wide range in photon energies. These detectors (also known as AXUV photodiodes) have a flat spectral power response from ultraviolet to x-ray energies, and with a slightly reduced efficiency all the way down to visible wavelengths. Since they can be made small, multichannel detectors allow high spatial resolution to be combined with an intrinsic high temporal resolution, which can reach the microsecond range, depending on the application. Additional features include ease of use and installation, and relatively low cost compared to other techniques. A combination of two multichannel toroidally viewing systems has been recently installed on the Alcator C-Mod tokamak. The first array, which is composed of 16 channels, sees tangentially the outer-half of the plasma at the midplane, and is used to measure the total power radiated. The second array, also located at the midplane, consists of 19 channels and views the edge of the plasma. This array has a 2 mm radial resolution, allowing, for example, the study of edge dynamics in high confinement (H mode) plasmas. Because these detectors are largely insensitive to neutral particles (at least at particle energies of interest), it is now possible to measure the radial distribution of neutral "radiated" power emissivity, by looking at the difference between these measurements and those obtained with standard bolometers. When neutrals are not important, we found a very good agreement between the AXUV detectors and standard bolometers. Examples of applications of these measurements to the study of edge H-mode dynamics, impurity injection, disruptions, and internal barrier formation, are described. Planned upgrades and new applications for Alcator C-Mod are also discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A neutral particle analyzer, based on the time-of-flight technique is scheduled to be installed on the Alcator C-Mod tokamak. The instrument was originally designed and used in the ZT-40 experiment, and later, briefly used on the CTX experiment at Los Alamos National Laboratory. The design consists of a chopper wheel mounted on a turbomolecular pump, a ∼2 m long flight tube, a Cu–Be secondary electron emitting surface, and an electron multiplier, which together are used as the neutral particle detector. Among the changes introduced in the system from the original design, of particular interest is the location of the instrument. The instrument is mounted behind a magnetic-type neutral particle analyzer and shares the same line of sight. Both of them can be scanned, poloidally down to the X point and tangentially to R/R0=0.7. This will enable us to compare neutral flux through two different techniques with an overlap in energies from ∼0.5–4 keV, with the instrument capable of detecting neutral particles with energies as low as ∼20 eV. This should aid in characterizing neutral and ion behavior at the edge of the tokamak plasma, especially near the X point. We will also describe changes made to the controls for improved versatility and ease of operation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Measurement of the global neutron production from the Alcator C-Mod tokamak has been done for all experimental operation in deuterium, which commenced in August 1993. Up to 3×1012 neutrons/s have been measured for diverse plasmas, including high current (1 MA), pellet injected, and rf heated discharges. Measurements during the initial run period were obtained using two sets of neutron detectors housed in polyethylene loaded moderator stations. Two more moderator stations containing additional neutron detectors have been obtained from LLNL and have been installed in the Alcator C-Mod experimental cell. The system has been calibrated using Cf252 placed at discrete points inside the Alcator C-Mod vacuum vessel. This paper presents a description of the diagnostic, followed by details of the calibration method and results. A discussion of the derivation of ion temperature from the global measurements is included with first results from the integrated system. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: With a plasma current of up to 3 MA, toroidal field of up to 9 T, the confinement of the charged fusion products (CFPs) in Alcator C-Mod is expected to be excellent. For example, at maximum current and field, classical losses of the 0.8 MeV 3He, 1 MeV triton, 3 MeV proton, 3.5 and 3.7 MeV alphas are expected to be less than 5%. For the study of the global confinement of CFPs, we plan to measure the burnup of the 1 MeV triton (from the D–D reaction) using a proton recoil detector (NE-213) for the detection of the 14 MeV neutron resulting from the secondary fusion reaction (D–T). On the other hand, loss measurements of CFPs will be made inside the first wall with two detectors (one at the bottom, one at the midplane) using silicon based detectors. The midplane detector will be used to diagnose D–3He plasmas by looking at the unconfined 14.7 MeV proton. In addition to the derivation of fusion yield, energy distribution of the escaping protons will provide information about the ion velocity distribution of the reactants. The bottom detector is time, pitch angle and energy resolved, and thus will be used to study loss mechanisms such as first orbit, toroidal field ripple and magnetohydrodynamics-induced diffusion.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The range of detectable energies of the moveable fast ion probe on TFTR has been extended by the removal of a 3-μm Al foil across its entrance aperture. This foil formerly stopped hydrogenic ions with energies below 300 keV, and helium ions with energies below 900 keV. The new arrangement allows detection of neutral beam ions (100-keV D+) at toroidal fields between 1 and 5 T. Data typical of the probe's enhanced performance are shown.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1559-1566 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A radially movable detector located just below the outer midplane of the Tokamak Fusion Test Reactor (TFTR) [in Plasma Physics and Controlled Nuclear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 27] has been used to study the confinement of charged fusion products (CFP's). The scrape-off length of escaping CFP flux was measured using perturbative techniques based on shadowing the detector with different obstacles. Experimental results indicate the presence of a diffusive process for trapped particles. Derived diffusion step sizes were found to be in excellent agreement with those expected from toroidal magnetic field (TF) stochastic ripple diffusion.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1411-1414 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the confinement of the MeV ions that are created by D–D reactions in the TFTR tokamak [in Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 1, p. 27] is described. The ions that escape from the plasma are measured by a new type of detector located just outside the plasma edge. Most measurements made with this detector are consistent with the first-orbit loss of these ions. Exceptions are correlated with strong magnetohydrodynamic activity, and a preliminary explanation is presented.
    Type of Medium: Electronic Resource
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