Plasma diagnostics for the sustained spheromak physics experiment

In this article we present an overview of the plasma diagnostics operating or planned for the sustained spheromak physics experiment device now operat ing at Lawrence Livermore National Laboratory. A set of 46 wall-mounted mag netic probes provide the essential data necessary for magnetic reconstructi on 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 s pectrometer recording extended domain spectrometer for obtaining time-integ rated visible ultraviolet spectra and two time-resolved vacuum monochromete rs 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 c hannel photodiode spatial array gives radial emission profiles. Two-dimensi onal imaging of the plasma and helicity injector is provided by gated telev ision cameras and associated image-processing software. An array of fiber-c oupled photodetectors with H alpha filters view across the midplane and in the injector region to measure neutral hydrogen concentrations. Several nov el 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 meas urements to compare with an equilibrium code model fitted to wall-mounted p robes. The USPR is being designed to study edge density and turbulent fluct uations. A multipoint Thomson scattering system is currently being installe d to give radial temperature and density profiles. (C) 2001 American Instit ute of Physics.