Plasma diagnostics with a retarding potential analyzer

Summary form only given. The plasma rocket is located at NASA Johnson Space Center. To produce a thrust in space, an inert gas is ionized into a plasma and heated in the linear section of a tokamak fusion device to 1/spl times/10/sup 4/-1.16/spl times/10/sup 6/ K (/spl rho/=10/sup 10/-10/sup 14/ cm/sup -3/). The magnetic field used to contain the plasma has a magnitude of 2-10 kGauss. The plasma plume has a variable thrust and specific impulse. A high temperature retarding potential analyzer (RPA) is being developed to characterize the plasma in the plume and at the edge of the magnetically contained plasma. The RPA measures the energy and density of ions or electrons entering into its solid angle of collection. An oscilloscope displays the ion flux versus the collected current. All measurements are made relative to the facility ground. A RPA is being developed in a process which involves the investigation of several prototypes. The first prototype has been tested on a thermal plasma. The knowledge gained from its development and testing were applied to the development of a RPA for collimated plasma. To verify that the RPA is providing proper output, it is compared to the output from a Langmuir or Faraday probe.