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  • 1
    Electronic Resource
    Electronic Resource
    High resolution measurements of neutral density and ionization rate in the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 961-964 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.1319362
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  • 2
    Electronic Resource
    Electronic Resource
    High resolution bolometry on the Alcator C-Mod tokamak (invited) : 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. 260-264 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.1149309
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  • 3
    Electronic Resource
    Electronic Resource
    Applications of visible CCD cameras on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 935-939 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Five 7 mm diameter remote-head visible charge-coupled device (CCD) cameras are being used on Alcator C-Mod for several different diagnostic purposes. All of the cameras' detectors and optics are placed inside a magnetic field of up to 4 T. Images of the cameras are recorded simultaneously using two three-channel color framegrabber cards. Two CCD cameras are used typically to generate two-dimensional emissivity profiles of deuterium line radiation from the divertor. Interference filters are used to select the spectral line to be measured. The local emissivity is obtained by inverting the measured brightnesses assuming toroidal symmetry of the emission. Another use of the cameras is the identification and localization of impurity sources generated by the ion cyclotron radio frequency (ICRF) antennas, which supply the auxiliary heating on Alcator C-Mod. The impurities generated by the antennas are identified by correlating in time the injections seen at the cameras with measurements made with core diagnostics. Fibers whose views aligned with the camera views and whose outputs are coupled to a visible spectrometer are also used to identify the species of the impurities injected. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321010
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  • 4
    Electronic Resource
    Electronic Resource
    Diagnostic neutral beam and active spectroscopy requirements for the Alcator C-Mod tokamak (invited) : 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. 265-268 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Considerations are presented on the application of a diagnostic neutral beam to the Alcator C-Mod tokamak for active profile measurements of ion temperature, poloidal and toroidal rotation, impurity and minority species densities, and internal magnetic field. Calculations indicate that, for a typical 50 keV, 0.13 MW hydrogen beam, charge exchange recombination measurements for plasmas with line average densities up to 2.5×1020 m−3 will yield, with good signal-to-noise ratio and ∼1 cm spatial resolution, measurements of helium and low Z impurity density profiles with better than 1 ms time resolution, and ion temperature and rotation profiles with ∼1 ms time resolution. Motional Stark effect (MSE) measurements appear feasible over most of the operating density range of the device (at least up to 5×1020 m−3), also with ms time resolution. Spatial resolution of the MSE measurements will depend on the toroidal width of the beam and the angle of the view with respect to the beam; for a 5 cm wide beam with a 60° viewing angle, 2.5 cm spatial resolution is expected. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147821
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of Hα emissivities from line integrated brightness measurements on Alcator C-Mod : 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. 619-621 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Alcator C-Mod is equipped with a 227 chord visible light imaging system. Using a nonlinearly constrained least-squares algorithm, local emissivities have been obtained from the chordal brightness measurements without any assumptions about poloidal symmetry. The robustness of the inversion to noise and calibration errors as well as the spatial information (∼5-cm resolution) obtainable has been examined in detail. Some examples, demonstrating how results from the tomographic reconstruction of the Hα light can be used to calculate a particle confinement time and neutral density are given. Different interference filters in front of the arrays allow the same technique to be applied to other atomic species. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146305
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  • 6
    Electronic Resource
    Electronic Resource
    Alpha particle diagnostics using impurity pellet injection (invited) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4499-4504 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have proposed using impurity pellet injection to measure the energy distribution of the fast confined alpha particles in a reacting plasma [R. K. Fisher et al., Fusion Technol. 13, 536 (1988)]. The ablation cloud surrounding the injected pellet is thick enough that an equilibrium fraction F∞0(E) of the incident alphas should be neutralized as they pass through the cloud. By observing neutrals created in the large spatial region of the cloud which is expected to be dominated by the heliumlike ionization state, e.g., Li+ ions, we can determine the incident alpha distribution dnHe2+/dE from the measured energy distribution of neutral helium atoms dnHe0/dE using dnHe0/dE = dnHe2+/dE⋅F∞0 (E,Li+). Initial experiments were performed on the Texas Experimental Tokamak (TEXT) in which we compared pellet penetration with our impurity pellet ablation model [P. B. Parks et al., Nucl. Fusion 28, 477 (1988)], and measured the spatial distribution of various ionization states in carbon pellet clouds [R. K. Fisher et al., Rev. Sci. Instrum. 61, 3196 (1990)]. Experiments have recently begun on the Tokamak Fusion Test Reactor (TFTR) with the goal of measuring the alpha particle energy distribution during D–T operation in 1993–94. A series of preliminary experiments are planned to test the diagnostic concept. The first experiments will observe neutrals from beam-injected deuterium ions and the high energy 3He tail produced during ion cyclotron (ICH) minority heating on TFTR interacting with the cloud. We will also monitor by line radiation the charge state distributions in lithium, boron, and carbon clouds. Later experiments are planned to measure the energy distribution of the 3.7 MeV alphas created by 3He–D reactions during ICH minority heating. Observations of 3.7 MeV alphas should allow single-particle alpha physics to be studied now and result in a fully tested diagnostic prior to D–T operation of TFTR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143705
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  • 7
    Electronic Resource
    Electronic Resource
    The high resolution video capture system on the alcator C-Mod tokamak : 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. 947-950 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new system for routine digitization of video images is presently operating on the Alcator C-Mod tokamak. The PC-based system features high resolution video capture, storage, and retrieval. The captured images are stored temporarily on the PC, but are eventually written to CD. Video is captured from one of five filtered RS-170 CCD cameras at 30 frames per second (fps) with 640×480 pixel resolution. In addition, the system can digitize the output from a filtered Kodak Ektapro EM Digital Camera which captures images at 1000 fps with 239×192 resolution. Present views of this set of cameras include a wide angle and a tangential view of the plasma, two high resolution views of gas puff capillaries embedded in the plasma facing components, and a view of ablating, high speed Li pellets. The system is being used to study (1) the structure and location of visible emissions (including MARFEs) from the main plasma and divertor, (2) asymmetries in gas puff plumes due to flows in the scrape-off layer (SOL), and (3) the tilt and cigar-shaped spatial structure of the Li pellet ablation cloud. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147721
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  • 8
    Electronic Resource
    Electronic Resource
    The visible, imaging diode arrays on Alcator C-Mod : 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. 555-557 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A set of multichord, absolutely calibrated viewing arrays has been used to measure the distributions of H/D and C+2 emissions. A total of 227 chordal views are available, with the chords separated at the plasma by ∼1 cm typically. The chord brightness profiles have been combined and inverted (without recourse to symmetry assumptions) to yield local volume emission rates. Because of the thickness of the superstructure surrounding Alcator C-Mod, the views are from points re-entrant to the vacuum vessel. All but one of the arrays employ 64-channel, linear diode arrays, which are read out serially, thus requiring only one digitizer channel per array. Variable frame rates (∼1 Hz to ∼3.5 kHz) result in an extremely large dynamic range for these detectors. A 35-channel diode array which is read out in parallel and can track fast events like ELMs or pellets is also in use. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146349
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  • 9
    Electronic Resource
    Electronic Resource
    Measurements of molybdenum radiation in the Alcator C-Mod tokamak using a multilayer mirror soft x-ray polychromator : 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. 561-563 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A photometrically calibrated polychromator utilizing layered synthetic microstructure coated flats (also known as multilayer mirrors, MLMs) as dispersive elements is operating on the Alcator C-Mod tokamak to measure the molybdenum emissions in the XUV. Molybdenum, the first wall material in C-Mod, is the dominant high Z impurity in the plasma. Three spectral regions are measured by three separate MLM-detector channels. The characteristic charge states in the region between 30–40 A(ring) are Mo xv to Mo xx, between 65–90 A(ring) are Mo xxiv to Mo xxvi, and between 110–130 A(ring) are Mo xxxi and Mo xxxii. The instrument's spectral resolution varies from 0.4 A(ring) at λ=30 A(ring) to 7 A(ring) at λ=130 A(ring). The temporal resolution is typically 1.0 ms, but sampling rates of less than 1 ms are possible. The instrument was photometrically calibrated at The Johns Hopkins University using a Manson soft x-ray light source. Power loss estimates from Mo xxiv to Mo xxvi, Mo xxxi, and Mo xxxii have been obtained during ohmic and ICRF plasmas using the mist transport code to model the molybdenum charge state distributions in the plasma. The Mo concentrations have also been determined. Mo contributes ∼0.1 to the Zeff of 1.3 during ohmic plasmas. This contribution increases during ICRF heating to ∼0.5 of the Zeff of 2. The polychromator functions as a time-resolved soft x-ray emission power loss monitor. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146352
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  • 10
    Electronic Resource
    Electronic Resource
    Spectroscopic measurement of impurity transport coefficients and penetration efficiencies in Alcator C-Mod plasmas : 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. 636-638 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146311
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