Ken-Ichi Onoe

Discharge features in a steady-state nitrogen arcjet engine with an expansion nozzle

Nitrogen discharges in a 10-kW-class water-cooled arcjet engine were studied by means of spectroscopic diagnostics. The atomic excitation temperature and electron density in the constrictor increased from 15,000 to 18,000 K and from 1/spl times/10/sup 15/ to 2/spl times/10/sup 16/ cm/sup /spl minus/3/, respectively, with input power levels of 7-11 kW. An increase in the mass flow rate raised the electron density because of enhanced thermal pinch effect of the arc column. In the expansion nozzle, the pressure and electron density decreased drastically downstream, and therefore the plasma was expected to be in high non-equilibrium. The N/sub 2//sup +/ vibrational temperature reached about 6,000 K at the nozzle exit, and the N/sub 2//sup +/ rotational temperature decreased gradually resulting in a range of 1,000-2,500 K. >

Plasma Generation by Resonant-Cavity Microwave Discharge and Its Applications for Material Processing

A 2.45-GHz-microwave plasma source with a resonant cavity was studied for material processing under medium to atmospheric pressures. Stable plasmas, with electron temperature and density of 1 to 5 eV and beyond the plasma cutoff density, respectively, were efficiently sustained in an ambient pressure of 10-2-10 kPa with hydrogen, helium, nitrogen, argon and a mixture of H2+2H2 (vol. rate). The operational characteristics of coupling efficiency and cavity length depended on gas species. From electric fields measured on the cavity inner wall, the electromagnetic field pattern of TM011 resonance mode was expected to be excited in the cavity over a wide range of operational conditions. In addition, operation of a plasmajet generator, into which the plasma source was modified, diamond film synthesis and surface modification due to atomic oxygen were demonstrated.

Microwave Ion Source Using Resonant Cavity

Ring-cusped magnetic-field ion sources using 2.45-GHz-microwave resonant cavities were studied to develop high-performance compact ion sources for economically assisting material processings. The minimum flow rate required to sustain discharge was 10 sccm for weak-B-field off-resonance discharge in the TM011-mode-excitation cylindrical cavity, 6 sccm for weak-B-field discharge in the reentrant coaxial cavity, in which a stronger electric field was generated compared with that in the cylindrical cavity, and 3 sccm for electron cyclotron resonance (ECR) discharge in the cylindrical cavity. As a result of ion beam extraction, the highest mass utilization efficiency of 18.7% was achieved for ECR discharge.

Long plasma generation using microwave slot antennas on a rectangular waveguide

30‐cm‐class long plasmas were generated using 2.45‐GHz microwave slot antennas on a rectangular waveguide with a T‐shaped ridge for the development of high performance ion sources or for plasma reactors for large‐area material processing. The microwave coupling efficiencies above 85% were achieved for Ar, N2, and O2 over large flow rate ranges. From the electric fields on the inner wall E side of the waveguide, standing waves with the maximum electric field strength of about 30 kV/m were expected to be excited in the waveguide, depending on the location of the T‐shaped ridge. The plasma density for Ar was in the order of 1017 m−3 and for N2 and O2 1016 m−3 in a discharge chamber in front of the slot antennas. The electron temperature for Ar ranged from 3 to 4 eV and for N2 and O2 from 3 to 8 eV. The spatial profiles of the ion saturation current for Ar were almost flat in the discharge chamber although the profiles for N2 and O2, with large flow rates or near the antennas, were slightly rough.

DEVELOPMENT OF A REENTRANT-CAVITY-TYPE ELECTRON CYCLOTRON RESONANCE (ECR) ION SOURCE AND ITS APPLICATIONS FOR MATERIAL PROCESSING

An Electron Cyclotron Resonance (ECR) ion source using a reentrant coaxial cavity was newly developed. The reentrant coaxial cavity forces microwaves to propagate into plasmas from an annular window of a discharge chamber side wall. Uniform plasmas were obtained above 10 sccm of a mass flow rate for Ar. On the axis of the discharge chamber, the plasma density was higher than the cutoff density for Ar, although lower for O 2 and N 2 . The maximum ion beam current of 63.5 mA was obtained at a forward power of 304 W for Ar.

Performance characteristics of a sheet-shaped microwave ion source using slot antennas on a rectangular waveguide

A 30-cm-class sheet-shaped 2.45-GHz-microwave ion source using slot antennas on a rectangular waveguide with a T-shaped ridge was newly developed. The microwave coupling efficiencies above 85% were achieved for Ar, N 2 and O 2 over large flow rate ranges. The plasma density for Ar was in an order of 10 17 m -3 and for N 2 and O 2 of 10 16 m -3 . The electron temperature for Ar ranged from 3 to 4 eV and for N 2 and O 2 from 3 to 8 eV. The spatial profiles of the ion saturation current for Ar were almost flat in the discharge chamber although the profiles for N 2 and O 2 , with large flow rates or near the slot antennas, were slightly rough. As a result, the maximum ion current of 60 mA with a beam size 70 × 280 mm for Ar was achieved at a beam voltage of 400 V.