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  • 11
    Electronic Resource
    Electronic Resource
    Multiple electron stripping of 3.4 MeV/amu Kr7+ and Xe11+ in nitrogen (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1753-1756 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Use of heavy ions beams with ∼10 MeV/amu mass ∼200, and average charge state of 1+ has been proposed as a driver for heavy ion fusion. Stripping of the ion beam by background gas can lead to an increase in the space charge density of the beam, which may make focusing the intense ion beam onto small targets more complex. Knowledge of the electron loss cross sections is essential to understand and address the problem. Currently, there are no 10 MeV/amu mass=200, charge state=1 beams available, and the theories that calculate electron loss cross sections can be experimentally tested only by using available beams of somewhat lower energy and higher initial charge state. The charge state distribution of ions produced in single collisions of 3.4 MeV/amu Kr7+ and 3.4 MeV/amu Xe11+ in N2 have been measured at the Texas A&M Cyclotron Institute using a windowless gas cell. The charge states of the outgoing ions are determined by magnetic analysis using a position-sensitive microchannel-plate detector. The cross sections for single and multiple electron loss are determined, and the results indicate that substantial multiple-electron loss occurs. The relative cross section for loss of i+1 electrons is 0.3–0.7 times that for i electron loss. The average number of electrons removed per one collision (sum of the electron-weighted cross sections normalized to the total cross section) is 1.86 for Kr and 1.97 for Xe. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1365408
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  • 12
    Electronic Resource
    Electronic Resource
    Tests of local transport theory and reduced wall impurity influx with highly radiative plasmas in the Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 877-884 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron temperature (Te) profile in neutral beam-heated supershot plasmas (Te0∼6–7 keV ion temperature Ti0∼15–20 keV, beam power Pb∼16 MW) was remarkably invariant when radiative losses were increased significantly through gas puffing of krypton and xenon in the Tokamak Fusion Test Reactor [McGuire et al., Phys. Plasmas 2, 2176 (1995)]. Trace impurity concentrations (nz/ne∼10−3) generated almost flat and centrally peaked radiation profiles, respectively, and increased the radiative losses to 45%–90% of the input power (from the normal ∼25%). Energy confinement was not degraded at radiated power fractions up to 80%. A 20%–30% increase in Ti, in spite of an increase in ion–electron power loss, implies a factor of ∼3 drop in the local ion thermal diffusivity. These experiments form the basis for a nearly ideal test of transport theory, since the change in the beam heating power profile is modest, while the distribution of power flow between (1) radiation and (2) conduction plus convection changes radically and is locally measurable. The decrease in Te was significantly less than predicted by two transport models and may provide important tests of more complete transport models. At input power levels of 30 MW, the increased radiation eliminated the catastrophic carbon influx (carbon "bloom") and performance (energy confinement and neutron production) was improved significantly relative to that of matched shots without impurity gas puffing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873327
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  • 13
    Electronic Resource
    Electronic Resource
    Observation of particle transport barriers in reverse shear plasmas on the Tokamak Fusion Test Reactor : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1832-1838 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perturbative experiments on the Tokamak Fusion Test Reactor [Phys. Plasmas 4, 1736 (1997)] (TFTR) have investigated transport in reverse shear plasmas. On TFTR, reverse magnetic shear plasmas bifurcate into two states with different transport properties: reverse shear (RS) and enhanced reverse shear (ERS) with improved core confinement. Measurements of the 14 MeV t(d,n)α neutrons and charge-exchange recombination radiation spectra are used to infer the trace tritium and helium profiles, respectively. The profile evolution indicate the formation of core particle transport barriers in ERS plasmas. The transport barrier is manifested by an order-of-magnitude reduction in the particle diffusivity (DT,DHe) and a smaller reduction in the pinch within the reverse shear region. The low diffusivities are consistent with neoclassical predictions. Furthermore, DT and DHe(approximate)χeff, the effective thermal diffusivity. Although the measured coefficients imply no helium ash accumulation, the situation is uncertain in a reactor due to unknown χeff scaling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872853
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  • 14
    Electronic Resource
    Electronic Resource
    Scaling of Ohmic energy confinement with major radius in the Tokamak Fusion Test Reactor (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3996-4001 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ohmic plasma size scans have been carried out in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)] to measure the influence of the major radius upon energy confinement. The major radius, minor radius, and aspect ratio were varied over wide ranges (R=2.08–3.2 m, a=0.4–0.9 m, and R/a=2.9–8.0) at constant qc. The energy confinement determined from kinetic diagnostics varies strongly with major radius. The data set is less well suited to determine minor radius scaling, but it appears to be distinctly weaker than the major radius scaling. The anomaly in ion thermal conductivity over neoclassical predictions appears to decline with increasing aspect ratio, which is a better ordering parameter for the magnitude of the anomaly than either the minor radius or the major radius. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870869
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  • 15
    Electronic Resource
    Electronic Resource
    In-vessel tritium measurements using beta decay in the Tokamak Fusion Test Reactor : 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. 1119-1122 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Tritium on the inside walls of the Tokamak Fusion Test Reactor was detected by configuring the vacuum vessel as an ionization chamber and measuring the secondary electron current from the tritium beta decay. The vessel was typically filled with (approximate)5 Torr of dry nitrogen and the secondary electron current was collected by an internal electrode biased to about +15 V with respect to the vessel wall. The measured variations of the collected current with gas pressure, bias voltage, and applied magnetic fields are described, as well as an in situ calibration made by injecting a known amount of tritium gas. Improved versions of this diagnostic may be useful to track the in-vessel content of surface tritium in future fusion devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149294
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  • 16
    Electronic Resource
    Electronic Resource
    Fast wavelength switching of narrow-band excimer lasers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2965-2968 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel system was developed, which allows one to switch the wavelength of a narrow-band excimer laser between two successive light pulses at a repetition rate of at least 250 Hz. This is realized by a periodically driven piezo actuator, which is attached to the diffraction grating of the narrow-band KrF excimer laser. The achieved position accuracy of the grating leads to a wavelength reproducibility of ±0.2 pm, which allows one to apply this system to laser spectroscopic investigations like LIF or LIPF of OH in flames. Using the fast wavelength switching system background reduced concentration and temperature fields in flames can be measured within one sequence. Some possible realized and planned applications like the measurement of gas temperature, the diagnostic of turbulent combustion processes, and the investigation of combustion processes under microgravity are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148227
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  • 17
    Electronic Resource
    Electronic Resource
    Methods for the measuring surface tritium inside TFTR using beta decay : 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. 357-359 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Three potential methods for evaluating the surface tritium content of the TFTR vacuum vessel are described, each based on a different technique for measuring the in situ beta emission from tritium. These methods should be able to provide both a local and a global assessment of the tritium content within the top ≈1 μm of the inner wall surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146410
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  • 18
    Electronic Resource
    Electronic Resource
    PLT and PDX perpendicular charge exchange analyzers (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1794-1796 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The perpendicular charge-exchange systems used on the poloidal divertor experiment and the Princeton large torus are comprised of ten-channel, mass-resolved, charge-exchange analyzers. Results from these systems indicate that instrumental effects can lead to erroneous temperature measurements during deuterium neutral beam injection or at low hydrogen concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139185
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  • 19
    Electronic Resource
    Electronic Resource
    Magnetic diagnostics and feedback control on TFTR (invited) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 941-946 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The various operating modes of TFTR require the use of a sophisticated system of magnetic diagnostics integrated with a feedback control system. This system has successfully controlled the plasma current and position over a range of major and minor radii, during strong compression, and will soon be used during intense neutral beam heating. Current and position values are held constant to within 2 kA and 1 cm. A wide variety of preoperational field measurements were required to determine proper compensation for dynamic stray fields due to eddy currents. Data from plasma profile diagnostics, such as bolometer arrays, Thomson scattering, soft x-ray diode array, and the scanning radiometer, have been compared to the absolute position deduced from magnetics. In addition to control functions, magnetic diagnostics on TFTR provide data on plasma current asymmetry, βθ, MHD fluctuations, loop voltage, and flux consumption. This paper will discuss the mechanical and electronic design constraints, as well as the analytic and calibration techniques required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138056
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  • 20
    Electronic Resource
    Electronic Resource
    Possible origin of the anomalous magnetization behavior in melt-textured Y1Ba2Cu3O7−δ crystallites (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 406-408 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization measurements of the hysteresis loop, M(B), of melt-textured Y1Ba2Cu3O7−δ (YBCO) crystallites were performed in external magnetic fields up to 10 T. The M(B) curves exhibit, between the superconducting transition temperature Tc and almost 39 K, a peak at a finite field B* which increases with decreasing temperature. The crystallites possess a high density of dislocations which could have been introduced during the high temperature treatment and/or by stresses created due to differences in the lattice parameter of small inclusions and the YBCO matrix. The large dislocation density together with the high sensitivity of the superconducting order parameter on deviations from the regular crystal structure and the small coherence length are suggested to be responsible for the observed fishtail shape of the magnetization curves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110033
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