Engineering topics

Wada, M

Publications and source records attributed to Wada, M.

10 records

DOE OSTI2012

Comparison between single- and dual-electrode ion source systems for low-energy ion transport

Extraction of ions with energies below 100 eV has been demonstrated using a hot-cathode multi-cusp ion source equipped with extraction electrodes made of thin wires. Two electrode geometries, a single-electrode system, and a dual-electrode system were built and tested. The single-electrode configuration showed high ion beam current densities at shorter distances from the electrode but exhibited rapid attenuation as the distance from the electrode increased. Beam angular spread measurements showed similar beam divergence for both electrode configurations at low plasma densities. At high plasma densities and low extraction potentials, the single-electrode system showed the angular spread twice as large as that of the dual-electrode system. Energy distribution analyses showed a broader energy spread for ion beams extracted from a single-electrode set-up.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

Development of a He{sup -} and He{sup 0} beam source for alpha particle measurement in a burning plasma

Proof of principle experiments of neutral helium beam production for alpha particle diagnostics was carried out on a test stand. Negative helium ions were produced in the Li charge exchange cell, in which stable and long time operation was possible. He{sup -} beam was accelerated to 157 keV. Finally, He{sup 0} beam was successfully produced after the flight in the drift-tube through the auto-electron-detachment process from He{sup -} to He{sup 0}. A neutral beam detector using a pyroelectric device was also developed to measure He{sup 0} beam intensity. The metastable component in the neutral helium beam was found to be less than 2%.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2012

High frequency operation of a hot filament cathode for a magnetized plasma ion source

A tungsten filament cathode has been operated with an ac heating current to excite a plasma in a linear magnetic field. Both the discharge current and the ion saturation current in plasma near the extraction hole of the ion source exhibited fluctuations. The discharge current fluctuated with the amplitude less than 2% of the average, and the frequency two times the frequency of the heating current. Fluctuation amplitude of the ion saturation current was about 10% of the average, while the frequency was the same as that of the heating current. The ac operation has prolonged the lifetime of a hot filament cathode by about 50%.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Extraction of negative hydrogen ions from a compact 14 GHz microwave ion source

A pair of permanent magnets has formed enough intensity to realize electron cyclotron resonance condition for a 14 GHz microwave in a 2 cm diameter 9 cm long alumina discharge chamber. A three-electrode extraction system assembled in a magnetic shielding has formed a stable beam of negative hydrogen ions (H{sup -}) in a direction perpendicular to the magnetic field. The measured H{sup -} current density was about 1 mA/cm{sup 2} with only 50 W of discharge power, but the beam intensity had shown saturation against further increase in microwave power. The beam current decreased monotonically against increasing pressure.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

Hollow target magnetron-sputter-type solid material ion source

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al{sup +} and Ar{sup +} ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 {mu}A, with the Al{sup +} ion beam occupying 30% of the total beam current.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2012

Ion energy distribution functions of low energy beams formed by wire extraction electrodes

The two-electrode extractor system made of 0.1 mm diameter tungsten wires separated by 0.7 mm has formed an argon ion beam with 50 V extraction potential. Energy spreads of the extracted beams were typically less than 2 eV when the beam current density was low. The beam intensity rapidly decreased as the distance between the extractor and the beam detector increased, indicating space charge limited transport of the beam. Problems associated with the emittance measurements are also discussed.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

An alpha particle measurement system using an energetic neutral helium beam in ITER (invited)

An energetic helium neutral beam is involved in the beam neutralization measurement system of alpha particles confined in a DT fusion plasma. A full size strong-focusing He{sup +} ion source (2 A, the beam radius of 11.3 mm, the beam energy less than 20 keV). Present strong-focusing He{sup +} ion source shows an emittance diagram separated for each beamlet of multiple apertures without phase space mixing, despite the space charge of a beamlet is asymmetric and the beam flow is non-laminar. The emittance of beamlets in the peripheral region was larger than that of center. The heat load to the plasma electrode was studied to estimate the duty factor for the ITER application.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Effects of adsorption and roughness upon the collision processes at the convertor surface of a plasma sputter negative ion source

Atomic collision processes associated with surface production of negative hydrogen ions (H{sup -}) by particle reflection at molybdenum surface immersed in hydrogen plasma have been investigated. To calculate sputtering yields of Cs, as well as energy spectra and angular distributions of reflected hydrogen atoms from molybdenum surface by H{sup +} ion and Cs{sup +} ion bombardments, a Monte Carlo simulation code ACAT (Atomic Collision in Amorphous Target) was run with the corresponding surface conditions. A fractal surface model has been developed and adopted to ACAT for evaluating the effect due to roughness of target material. The results obtained with ACAT have indicated that the retention of hydrogen atoms leads to the reduction in sputtering yields of Cs, and the surface roughness does largely affect the sputtering yields of Cs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2012

Extraction of a strongly focusing He{sup +} beam from three-stage concave electrodes for alpha particle measurement system in ITER

A strongly focusing He{sup +} ion beam source equipped with concave multi-aperture electrodes was developed for production of He{sup -} through a charge exchange cell. The beam was extracted at a voltage less than 20 kV from 301 apertures distributed in an area of 100 mm {phi}, and focused at 750 mm distance. The beam current and the beam size of 2 A and 20 mm in diameter, respectively, were achieved with an arc power less than 10 kW. The optimum perveance was obtained at 0.02 A/kV{sup 1.5} at the beam energy less than 20 keV which is suitable for the conversion to He{sup -} in an alkali vapor cell.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

Characteristics of low-energy ion beams extracted from a wire electrode geometry

Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm{sup 2} with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm{sup 2} for a 50 eV ion beam and 1.78 mA/cm{sup 2} for a 100 eV ion beam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗