Development of a HELIOS Diagnostic for the Prototype Material Plasma Exposure eXperiment

A new helium line-ratio spectral monitoring (HELIOS) diagnostic is being implemented on Oak Ridge National Laboratory’s (ORNL) Prototype Material Plasma Exposure eXperiment (Proto-MPEX).  The HELIOS diagnostic is constructed so that the puffed He gas outlet is as close to the plasma column as possible.  Fiber optics transfer the light emission from the plasma to a Filterscope system where the intensity is measured at a sampling rate of 100 kHz for three separate helium lines: 667.9 nm, 706.53 nm, and 728.0 nm.  The open magnetic geometry of Proto-MPEX allows for the comparison of the HELIOS derived n_e and T_e values to nearby double Langmuir probes (DLP) and Thomson scattering (TS) measurements.  The HELIOS system (100 kHz) should provide n_e and T_e at much higher rates than either the DLP (200 Hz) or TS (10 Hz).  HELIOS measurements, however, are complicated by line-of-sight integration issues and the low temperature of Proto-MPEX require collisional radiative model (CRM) calculations to be extended beyond the range traditionally used in previous tokamak measurements. Preliminary HELIOS measurements give edge T_e values of 5 - 8 eV and edge density values of 3e18 m^-3 – 6e18 m^-3.

This work was supported by the US. D.O.E. contract DE-AC05-00OR22725 and DE-SC00013911.