The edge plasma of the ORNL CAPRICE ECR ion source is studied by directly measuring, with electrical probes, its local plasma parameters such as plasma density, temperature and electron energy distribution characteristics at different rf power levels, at various pressures, at various axial magnetic field strengths and different distances from the resonant zone. It is found that the edge plasma can be approximated to be bi-Maxwellian, whose characteristics become more pronounced at the more distant positions from the ECR zone, at lower source pressures and at increased magnetic field strengths. These trends are consistently explained in terms of long-range electron-electron and electron-ion Coulomb scattering collisions that occur during the transport of hot electrons from the ECR plasma to the probe and their frequency dependence on electron temperature and density.

Hydrogen is produced by direct dissociation of water vapor, i.e., splitting water molecules by the electrons in water plasma at low pressure (<10-50 Torr) using microwave plasma discharge. This condition generates a high electron temperature, which facilitates the direct dissociation of water molecules. A microwave plasma source is developed, utilizing the magnetron of a microwave oven and a TE10 rectangular waveguide. The quantity of the generated hydrogen is measured using a residual gas analyzer. The electron density and temperature are measured by a Langmuir probe, and the neutral temperature is calculated from the OH line intensity.

DiPS (Diversified Plasma Simulator), a new versatile linear machine (length=3400 mm, diameter=200-600 mm), is developed for the simulations of divertor, space and processing plasmas with various electric probes: fast-scanning systems with single, triple, and Mach Probes, slow-scanning water-cooled single probe, griddedenergy analyzer (GEA), and several fixed single probes. For the verification of current probe theories and the development of new theories with magnetic vector field, collisional effects, various particle sources, and wide range of plasma parameters, two different plasma sources are installed: (1) For a stable high density dc plasma, a LaB6 disk is used as the thermal electron emission source with 5 kW graphite heater. Initial plasma density of the LaB6 source is 5 × 10 12 cm −3 , electron temperature is 8-10 eV with magnetic field around 1 kG. The electron density would be decreased severely, i.e., to 10 6 − 10 8 cm −3 with grid, and expanded into space simulation region without magnetic field; (2) Helicon plasma source is also installed for a processing simulation in DiPS and for the space propulsion study with magnetic expansion, which generates the plasma with density of 2 × 10 13 cm −3 and electron temperature 3-4 eV for the rf power of 2.5 kW at optimum pressure of 7.5 mTorr. As a unique feature for the diversified uses of sources and divertor simulator experiments, space and processing simulation chambers can be detached from and attached to the divertor simulation chamber on the rail. Initial data of various electric probes (single, triple, emissive, mach probes, GEA, etc.) are introduced for the the following conditions of DiPS with B= 1 kG, P= 130 mTorr at source region, P= 2 mTorr at divertor simulation region, ne = 1× 10 12 − 1 × 10 14 cm −3 , Te = 2 -3 eV, Ti = 0.2 eV with laser induced fluorescence (LIF) (Ar gas), ne = 1 × 10 12 − 1 × 10 13 cm −3 , Te =5 -6 eV (He gas) at divertor simulation region, Ti = 0.47 -0.74 eV with GEA at space simulation region and v d = 500 -600 m/s.

The electron densities in the argon plasmas of the ORNL 6 GHz electron cyclotron resonance (ECR) ion source with a flat central magnetic field have been deduced from the ion branches of the electric probe current-voltage curves measured in the edge region of the plasmas. To overcome the difficulties due to unknown velocities of multiply charged ions at the sheath edge, a modified generalized Bohm criterion for the ion sheath velocity is introduced and the mean velocity of all ionic charge states at the sheath edge is assumed to be equal to the sound velocity of the system of particles. The calculated electron densities and temperatures for different plasmas optimized for four charge state distributions are discussed.