Plasma diagnostics for the sustained spheromak physics experiment

Abstract

In this article we present an overview of the plasma diagnostics operating or planned for the sustained spheromak physics experiment device now operating at Lawrence Livermore National Laboratory. A set of 46 wall-mounted magnetic probes provide the essential data necessary for magnetic reconstruction of the Taylor relaxed state. Rogowski coils measure currents induced in the flux conserver. A CO2 laser interferometer is used to measure electron line density. Spectroscopic measurements include an absolutely-calibrated spectrometer recording extended domain spectrometer for obtaining time-integrated visible ultraviolet spectra and two time-resolved vacuum monochrometers for studying the time evolution of two separate emission lines. Another time-integrated spectrometer records spectra in the visible range. Filtered silicon photodiode bolometers provide total power measurements, and a 16 channel photodiode spatial array gives radial emission profiles. Two-dimensional imaging of the plasma and helicity injector is provided by gated television cameras and associated image-processing software. An array of fiber-coupled photodetectors with H alpha filters view across the midplane and in the injector region to measure neutral hydrogen concentrations. Several novel diagnostics are being fielded including a transient internal probe (TIP) and an ultrashort-pulse reflectometer (USPR) microwave reflectometer. The TIP probe fires a very high velocity optical bullet through the plasma and will provide fairly nonpertabative internal magnetic field and current measurements to compare with an equilibrium code model fitted to wall-mounted probes. The USPR is being designed to study edge density and turbulent fluctuations. A multipoint Thomson scattering system is currently being installed to give radial temperature and density profiles.

Spheromak formation and sustainment studies at the sustained spheromak physics experiment using high-speed imaging and magnetic diagnostics

“…A diverse set of diagnostics has been implemented to measure the spheromak internal density, temperature, and magnetic field. [2][3][4] Many diagnostics have access to the plasma through a midplane opening of the flux conserver, as shown in Fig. 1.…”

Measurements and phenomenological modeling of magnetic flux buildup in spheromak plasmas

“…Qualitatively, however, the signals were the same for both cases. Plasma density was measured using a CO 2 laser interferometer [14], and was relatively flat with values (0.5-1) × 10 20 m −3 for the shots discussed in Section III B.…”

The Search for Reconnection and Helicity During Formation of a Bounded Spheromak

“…For shots with the probe inserted, electron temperature has been measured using Thomson scattering [8] at 20 eV . Using…”