Feasibility study for a high-k temperature fluctuation diagnostic based on soft X-ray imaging

POSTER

Abstract

Turbulence transport can significantly limit fusion gain. A deep understanding of turbulent transport requires sufficient experimental data of turbulence quantities, such as the fluctuations of electron density and temperature. In this work, we explored the feasibility of using soft X-ray imaging to measure electron temperature fluctuations in NSTX-U, a spherical tokamak. We devised a pseudolocal tomography algorithm to reconstruct local electron temperature fluctuations from the measurements of line-integrated soft X-ray emissivity and a model to test this algorithm. The reconstructed wavenumber spectrum of the electron temperature fluctuations is optimized by varying the number of viewing chords and viewing angles of X-ray detectors to best match the synthetic wavenumber spectrum. The dependence of the reconstructed results on the relationship between the emissivity and the electron temperature is studied. A sensitivity analysis has also been done to demonstrate the requirements that the X-ray detector needs to fulfill if we want to build such a realistic diagnostic based on this idea. The requirements include the aperture, the time resolution, the electronic noise level and other factors.

* This work has been supported by US. D.O.E. contract DE-SC0019089. Computer simulations were carried out at the National Energy Research Scientific Computing Center, supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231 and at the MIT-PSFC partition of the Engaging cluster at the MGHPCC facility (www.mghpcc.org) which was funded by DoE grant number DE-FG02-91-ER54109.

Authors

  • Xiang Chen

    Massachusetts Institute of Technology MIT

  • J. Ruiz Ruiz

    University of Oxford, Oxford

  • N.T. Howard

    Massachusetts Institute of Technology MIT, MIT, MIT PSFC

  • Walter Guttenfelder

    Princeton Plasma Physics Laboratory, Princeton Plasma Physics Laboratory, Princeton, NJ, PPPL

  • J. Candy

    General Atomic, General Atomics, General Atomics - San Diego, GA

  • Jerry Hughes

    Massachusetts Institute of Technology MIT, MIT, Plasma Science and Fusion Center - MIT, Massachusetts Institute of Technology, Plasma Science and Fusion Center, MIT PSFC

  • Bob Granetz

    Massachusetts Institute of Technology MIT, Massachusetts Institute of Technology Plasma Science and Fusion Center, MIT

  • A.E. White

    Massachusetts Institute of Technology MIT, MIT, MIT Plasma Science and Fusion Center, Cambridge, USA