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  • 1
    Electronic Resource
    Electronic Resource
    Green light 2ω as an x-ray streak camera fiducial (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2187-2188 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The fiducial system for the multiple optical and x-ray streak cameras on the two Nova target chambers is intended to allow cross comparison of time-resolved data from laser plasmas to an accuracy of ±50 ps. Development of the system has led to the discovery that Al-coated fiber optics incorporated into the x-ray photocathode can be made to produce photoelectrons when irradiated by ∼1 μJ of 2ω light. The low loss and dispersion of 2ω light in fused silica fibers are significant advantages over our original intention of using 3ω light. Results indicating input and output pulse lengths and required energies to produce photoelectrons will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138726
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrafast turnoff laser triggered gating system for microchannel-plate intensified x-ray spectrometers (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 818-820 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A laser triggered photoconductive switch based microchannel-plate (MCP) gating system has been developed. The gating pulse provided to the MCP has a fall time on the order of 200 ps. Use of this system has resulted in increased signal-to-noise ratio on three MCP intensified x-ray spectrometers during recent x-ray experiments at the Novette laser facility. The x-ray signals of interest have a duration of approximately 300 ps while background in the same spectral region continues for several nanoseconds. As a result, signal-to-noise ratio is maximized by turning the MCP off just after the signals of interest are recorded. The MCP's are turned on by charging to approximately 1 kV with a slow rise-time (500 ns) pulse and rapidly gated off by a photoconductive switch connected to the MCP through transmission lines. Staggering the turnoff times of three microstrip lines across the MCP by 250 ps provides some time resolution. Details of the system, including pulse charging system, trigger beam delivery optics, and system diagnostics will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138183
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of the focused output from a selenium soft x-ray laser (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 786-788 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The output energy (90 μJ), focal spot diameter (235 μm), and pointing accuracy (±75 μrad) for a 3.7-cm-long Se soft x-ray laser operating at 20.6 and 20.9 nm are reported. Now that this intense soft x-ray source has been well characterized it may find use in such diverse applications as lithography, contact microscopy, holography, and photoionization pumping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101359
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  • 4
    Electronic Resource
    Electronic Resource
    The two-dimensional structure of radiative divertor plasmas in the DIII-D tokamak : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1761-1773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent measurements of the two-dimensional (2-D) spatial profiles of divertor plasma density, temperature, and emissivity in the DIII-D tokamak [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] under highly radiating conditions are presented. Data are obtained using a divertor Thomson scattering system and other diagnostics optimized for measuring the high electron densities and low temperatures in these detached divertor plasmas (ne≤1021 m−3, 0.5 eV≤Te). D2 gas injection in the divertor increases the plasma radiation and lowers Te to less than 2 eV in most of the divertor volume. Modeling shows that this temperature is low enough to allow ion–neutral collisions, charge exchange, and volume recombination to play significant roles in reducing the plasma pressure along the magnetic separatrix by a factor of 3–5, consistent with the measurements. Absolutely calibrated vacuum ultraviolet spectroscopy and 2-D images of impurity emission show that carbon radiation near the X-point, and deuterium radiation near the target plates contribute to the reduction in Te. Uniformity of radiated power (Prad) (within a factor of 2) along the outer divertor leg, with peak heat flux on the divertor target reduced fourfold, was obtained. A comparison with 2-D fluid simulations shows good agreement when physical sputtering and an ad hoc chemical sputtering source (0.5%) from the private flux region surface are used. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872278
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  • 5
    Electronic Resource
    Electronic Resource
    Motional Stark effect upgrades on DIII-D : 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. 373-375 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The measurement and control of the plasma current density profile (or q profile) is critical to the advanced tokamak program on DIII-D. A complete understanding of the stability and transport properties of advanced operating regimes requires detail poloidal field measurements over the entire plasma radius from the core to the edge. In support of this effort, we have recently completed an upgrade of the existing motional Stark effect (MSE) diagnostic, increasing the number of channels from 8 to 16. A new viewing geometry has been added to the outer edge of the plasma which improves the radial resolution in this region from 13 to ∼2 cm. This view requires the use of a reflector that has been designed to minimize polarization effects. Vacuum-compatible polarizers have also been added to the instrument for in situ calibration. Future use of the MSE diagnostic for feedback control of the q profile will also be discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146416
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  • 6
    Electronic Resource
    Electronic Resource
    Thomson scattering stray light reduction techniques using a CCD camera : 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. 704-707 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The DIII–D Thomson scattering system has been expanded to measure divertor plasma temperatures from 1 to 500 eV and densities from 0.05 to 8×1020 m−3. To complete this system, a difficult stray light problem was overcome to allow for an accurate Rayleigh scattering density calibration. The initial stray light levels were over 500 times higher than the expected Rayleigh scattered signal. Using a charge-coupled device (CCD) camera, various portions of the vessel interior were examined while the laser was fired through the vessel in air at atmospheric pressure. Image relaying, exit window tilting, entrance and exit baffle modifications, and a beam polarizer were then used to reduce the stray light to acceptable levels. The CCD camera gave prompt feedback on the effectiveness of each modification, without the need to reestablish vacuum conditions required when using the normal avalanche photodiode detectors (APD). Once the stray light was sufficiently reduced, the APD detectors provided the signal time history to more accurately identify the source location. We have also found that certain types of high reflectance dielectric coatings produce 10–15 times more scatter than other types of more conventional coatings. By using low-scatter mirror coatings and these new stray light reduction techniques, we now have more flexibility in the design of complex Thomson scattering configurations required to probe the central core and the new radiative divertor regions of the DIII–D vessel. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147679
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  • 7
    Electronic Resource
    Electronic Resource
    A 250-GHz microwave interferometer for divertor experiments on DIII-D : 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. 422-424 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new 250-GHz, two-frequency microwave interferometer system has been developed to diagnose divertor plasmas on DIII-D. This diagnostic will measure the line-averaged density across both the inner and outer, lower divertor legs. With a cutoff density of over 7×1014 cm−3, temporal measurements of edge localized modes (ELMs) and plasma detachment are expected. The outer-leg system will use a double-pass method while the inner-leg system will be single pass. Two special three-dimensional (3D) carbon composite tiles are used, one to protect the microwave antennas mounted directly under the strike point and the other as the outer-leg reflecting surface. Performance, design constraints, and the thermal-mechanical design of the 3D carbon composite tiles are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146365
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  • 8
    Electronic Resource
    Electronic Resource
    A tangentially viewing vacuum ultraviolet TV system for the DIII–D divertor : 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. 738-741 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A video camera system capable of imaging vacuum ultraviolet emission in the 120–160 nm wavelength range, from the entire divertor region in the DIII–D tokamak, was designed. The new system has a tangential view of the divertor similar to an existing tangential camera system [M. E. Fenstermacher et al., Rev. Sci. Instrum. 68, 974 (1997)] which has produced two-dimensional maps of visible line emission (400–800 nm) from deuterium and carbon in the divertor region. However, the overwhelming fraction of the power radiated by these elements is emitted by resonance transitions in the ultraviolet, namely the C IV line at 155.0 nm and Ly-α line at 121.6 nm. To image the ultraviolet light with an angular view including the inner wall and outer bias ring in DIII–D, a six-element optical system (f/8.9) was designed using a combination of reflective and refractive optics. This system will provide a spatial resolution of 1.2 cm in the object plane. An intermediate UV image formed in a secondary vacuum is converted to the visible by means of a phosphor plate and detected with a conventional charge injection device (CID) camera (30 ms framing rate). A single MgF2 lens serves as the vacuum interface between the primary and secondary vacuums; a second lens must be inserted in the secondary vacuum to correct the focus at 155 nm. Using the same tomographic inversion method employed for the visible TV, we will reconstruct the poloidal distribution of the UV divertor light. The grain size of the phosphor plate and the optical system aberrations limit the best focus spot size to 60 μm at the CID plane. The optical system is designed to withstand 350 °C vessel bakeout, 2 T magnetic fields, and disruption-induced accelerations of the vessel. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149286
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  • 9
    Electronic Resource
    Electronic Resource
    Simultaneous measurement of q and Er profiles using the motional Stark effect in high-performance DIII-D plasmas (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. 815-820 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The motional Stark effect (MSE) diagnostic was developed to provide a measurement of the magnetic pitch angle or q profile in tokamaks. The technique relies upon polarization measurements of Stark broadened Dα emission to determine the pitch angle of the Lorentz vb×B electric field, where vb is the injected neutral beam particle velocity and B is the total magnetic field. However, in many advanced confinement regimes, large values of the plasma radial electric field, Er, are observed and can affect the interpretation of MSE measurements. Viewing fixed locations in the plasma from two different viewing angles allows one to separate the Er field from the vb×B field, thus providing simultaneous measurement of the Er and q profiles. To achieve this measurement, the DIII–D MSE diagnostic was recently upgraded from 16 to 35 channels with three independent viewing angles. The new instrument provides an Er resolution of 5–10 kV/m with a time response of 1 ms. Measurement results from the VH mode, reverse shear, and H mode plasmas are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149317
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  • 10
    Electronic Resource
    Electronic Resource
    Design of the divertor Thomson scattering system on DIII-D : 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. 493-495 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Local measurements of ne and Te in the divertor region are necessary for a more complete understanding of divertor physics. We have designed an extension to the existing multipulse Thomson scattering system [Carlstrom et al., Rev. Sci. Instrum. 63, 4901 (1992)] to measure ne in the range 5×1018–5×1020 m−3 and Te in the range 5–500 eV with 1 cm resolution from 1 to 21 cm above the floor of the DIII-D vessel (eight spatial channels) in the region of the X point for lower single-null diverted plasmas. One of the existing, 20 Hz, Nd:YAG lasers will be redirected to a separate vertical port and viewed radially with a specially designed f/6.8 lens. Fiber optics carry the light to polychromators whose interference filters have been optimized for low Te measurements. Other aspects of the system, including the beam path to the vessel, polychromator design, real-time data acquisition, laser control, calibration facility, and DIII-D timing and data acquisition interface, will be shared with the existing multipulse Thomson system. An in situ laser alignment monitor will provide alignment information for each laser pulse. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146534
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