Simultaneous soft x-ray emissivity profile measurements in poloidally separate locations of the Alcator C-Mod edge plasma

Sunn Pedersen, T.; Pedersen, T. Sunn; Granetz, R. S.; Granetz, R.S.
September 2000
Review of Scientific Instruments;Sep2000, Vol. 71 Issue 9
Academic Journal
Two high resolution edge x-ray imaging diagnostics have been installed in the Alcator C-Mod tokamak. One array measures the radial soft x-ray emissivity profiles at the top of the plasma with 1.2 mm radial resolution, mapped along flux surfaces to the midplane, whereas the other measures the radial soft x-ray emissivity profiles at the outboard edge with 1.5 mm radial resolution mapped to the midplane. The two diagnostics measure the chord brightness profiles, which are then inverted to get soft x-ray emissivity simultaneously with a 12 μs sampling time. This allows us to determine if the soft x-ray emissivity, and therefore the fluorine density, is constant on a flux surface during steady state high confinement mode conditions, as well as during fast transient edge events, such as edge localized modes or transitions from the high confinement mode to the low confinement mode. Measurements are presented showing that the soft x-ray emissivity is not constant on a flux surface, but instead shows a large poloidal variation, contrary to what is assumed in the inversion routine. The effects of the poloidal variation on the inversion accuracy are estimated numerically. It is found that the emissivity is systematically overestimated at the top, and underestimated at the outboard edge, by less than 15%. The width of the x-ray emissivity pedestal is accurate to within 15%, and the location of the pedestal is accurate to within 1 mm. Measurements showing a poloidal propagation delay for the onset of the transition from high confinement mode (H mode) to low confinement mode (L mode) are also presented. © 2000 American Institute of Physics.


Related Articles

  • Mode number identification with a soft x-ray array Kaita, R.; Sesnic, S. // Review of Scientific Instruments;Jan1997, Vol. 68 Issue 1, p750 

    Describes a method using arrays of soft x-ray detectors for the determination of the toroidal and poloidal mode numbers of magnetohydrodynamic instabilities in tokamak plasmas. Toroidal mode number identification from maxima and minima in soft x-ray profiles; Phase difference observations in...

  • Code for time-resolved x-ray pulse analysis at high count rates for short tokamak discharges. Vega, J. // Review of Scientific Instruments;Oct90, Vol. 61 Issue 10, p3268 

    The measurement of soft x-ray spectrum in fusion plasmas allows for information on the nature of electron distribution, identification of impurity contents, calculation of electron temperature, estimation of Zeff, etc. All these measurements can be performed with a semiconductor detector. By...

  • Simulation of a tangential soft x-ray imaging system. Battaglia, D. J.; Shafer, M. W.; Unterberg, E. A.; Bell, R. E.; Hillis, D. L.; LeBlanc, B. P.; Maingi, R.; Sabbagh, S.; Stratton, B. C. // Review of Scientific Instruments;Oct2010, Vol. 81 Issue 10, p10E533 

    Tangentially viewing soft x-ray (SXR) cameras are capable of detecting nonaxisymmetric plasma structures in magnetically confined plasmas. They are particularly useful for studying stationary perturbations or phenomenon that occur on a timescale faster than the plasma rotation period. Tangential...

  • Extremely compact capillary discharge-based soft x-ray laser development and application to dense plasma diagnostics. Rocca, J. J.; Luther, B.; Marconi, M. C.; Whiteaker, T.; Braley, D. A.; Filevich, J.; Hammarsten, E. C.; Rahman, A.; Szapiro, B. T.; Wang, Y.; Jankowska, E.; Grisham, M.; Shlyaptsev, V. N.; Moon, S. // AIP Conference Proceedings;2002, Vol. 641 Issue 1, p125 

    We give an overview of recent capillary discharge-driven soft x-ray laser development experiments and applications ar Colorado State University. We report the demonstration of the first desktop size soft x-ray laser, a capillary discharge Ne-like Ar soft x-ray laser that was measured to emit...

  • The JET soft x-ray diagnostic systems Alper, B.; Dillon, S.; Edwards, A. W.; Gill, R. D.; Robins, R.; Wilson, D. J. // Review of Scientific Instruments;Jan1997, Vol. 68 Issue 1, p778 

    Describes the construction of a multicamera soft x-ray (SXR) detector system for the pumped divertor phase of the Joint European Torus tokamak to provide improved spatial and temporal resolution. Features of the SXR camera assemblies; Detector performance tests; Operational experience and...

  • New optical methods for short wavelength hot plasma diagnostics Kantsyrev, V.; Bruch, R. // Review of Scientific Instruments;Jan1997, Vol. 68 Issue 1, p725 

    Describes the development of experimental methods for high-temperature plasma diagnostics based on both glass capillary converters (GCC) and multilayer mirrors. Pinhole chamber with GCC; GCC converters for investigations of time dependent plasma phenomena in the soft x-ray region; High...

  • Soft x-ray tomography diagnostic for the Alcator C tokamak. Camacho, J. F.; Granetz, R. S. // Review of Scientific Instruments;Mar86, Vol. 57 Issue 3, p417 

    A soft x-ray tomography diagnostic has been built and operated on the Alcator C tokamak with the use of an 80-channel array of detectors. The detector system consists of miniature PIN photodiodes which are located around the periphery of the plasma at one toroidal location (top and bottom ports)...

  • Toroidal and poloidal soft x-ray imaging system on the DIII-D tokamak. Snider, R. T.; Evanko, R.; Haskovec, J. // Review of Scientific Instruments;Aug1988, Vol. 59 Issue 8, p1807 

    A toroidal soft x-ray imaging system is being added to the currently installed poloidal soft x-ray system on the DIII-D tokamak. The poloidal array is used to determine the poloidal mode structure and location of internal helical MHD perturbations in the plasma. The new array will add toroidal...

  • A photodiode for the measurement of soft x-ray radiation from plasma. Qingjun Xiao; Navratil, Gerald // Review of Scientific Instruments;Sep96, Vol. 67 Issue 9, p3334 

    Reports on the use of photodiodes as detectors on the high beta tokamak-extended pulse tokamak for soft x-ray radiation measurement. Sawteeth instabilities and magnetohydrodynamic oscillations found in the signals from the photodiodes.


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics