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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- beam was accelerated to 157 keV. Finally, He0 beam was successfully produced after the flight in the drift-tube through the auto-electron-detachment process from He- to He0. A neutral beam detector using a pyroelectric device was also developed to measure He0 beam intensity. The metastable component in the neutral helium beam was found to be less than 2%. [ABSTRACT FROM AUTHOR]

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+ ion source (2 A, the beam radius of 11.3 mm, the beam energy less than 20 keV). Present strong-focusing He+ 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. [ABSTRACT FROM AUTHOR]

A strongly focusing He+ ion beam source equipped with concave multi-aperture electrodes was developed for production of He- 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 [lowercase_phi_synonym], 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/kV1.5 at the beam energy less than 20 keV which is suitable for the conversion to He- in an alkali vapor cell. [ABSTRACT FROM AUTHOR]

Full orbit-following calculation is performed for the final orbit of the lost alpha particles, showing some orbits escaping from the last closed flux surface could be detected by a concealed lost ion probe (CLIP) installed under the shadow of the original first wall surface. While both passing and trapped orbits hit the same wall panel, detecting a trapped orbit by the CLIP is easier than detecting passing orbits. Whether the final orbit is detected or not is determined by the position of the reflection point. The CLIP successfully detects the trapped orbits, which are reflected before they hit to a first wall. Then the pitch angles of the orbits at the CLIP are close to and smaller than 90°. Optimization of the position of the CLIP in terms of broader detection window is investigated. [ABSTRACT FROM AUTHOR]

An orbit following calculation code with full gyromotion under the ITER magnetic field configuration has been developed to investigate escaping alpha particle orbits in ITER and to determine the geometrical arrangement for alpha particle detection. The code contained the full geometrical information of the first wall panels. It was carefully investigated whether an alpha particle escaping from the plasma through the last closed flux surface does not touch or intersect the first wall boundary before reaching the detection point. Candidates of blanket module modification have been studied to achieve effective measurement geometry for escaping alpha particle detection. The calculations showed that direct orbit loss and banana diffusion can be detected with a probe head recessed from the first wall surface. [ABSTRACT FROM AUTHOR]

A strongly focusing high-intensity He+ ion source equipped with three concave electrodes has been designed and constructed as the beam source for a high-energy He0 neutral beam probe system to diagnose fusion-produced alpha particles in thermonuclear fusion plasmas. The reduction of heat load onto the concave extraction electrodes is particularly important for a long pulse operation, as the heat load deforms the electrodes and thus the beam focal length. The effects on the arc efficiency (beam current/arc power) of the ion source due to the discharge filament structure (straight-type and L-shape-type filaments), size (filament diameters of 2 and 1.5 mm), number, and the locations have been studied. Choice of the appropriate filament structure improved the arc efficiency by 17%. [ABSTRACT FROM AUTHOR]

We have been developing a test stand for fast He0 beam production. One of the major issues is how to transport effectively the He+ and He- beams from which the He0 beam is produced. The beam should be focused in two transverse focal points, the center of the charge exchange cell and the electrostatic accelerator. We studied the beam transport system and effect of space charge neutralization in the test stand by experiments and calculation. [ABSTRACT FROM AUTHOR]

The beam neutralization system for measurement of the spatial and velocity distributions of alpha particles of ITER plasmas was studied. As forward angle detection against the beam injection direction is required for effective neutralization, arrangement of the measurement system using possible ports in ITER configuration is proposed. The count rate of neutralized alpha particles produced by the double charge exchange interaction with energetic He0 beam particles injected is estimated. The ratios of signal to neutron-induced noise are evaluated. When a He0 beam produced by autodetachment from a 1–1.5 MeV He- beam of 10 mA is injected, the signal to noise ratio becomes greater than 1 at ρ<0.4, even without beam modulation. Usage of a lock-in technique at the frequency of radio-frequency quadrapole accelerator will make measurement at the outer region possible. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline ceramics of Ce-doped Y3Al5O12 (Ce: YAG) is characterized as a candidate scintillator for a lost alpha particle measurement on a thermo-nuclear fusion experiments such as ITER. The luminescence intensity for polycrystalline Ce: YAG ceramics is investigated under MeV energy ion irradiation with the ion flux up to ∼6.7×1016 m−2 s−1 and with the ion fluence of ∼1.0×1019 m−2. The luminescence has a good linearity up to ion flux mentioned above. In view of the fluence, the luminescence degradation is observed, but it is found to be a tolerable level. In neutron and gamma ray irradiation experiments at a fission reactor, the defect such as blobs is appeared in irradiated samples. It is found that the thermal annealing is effective for the recovery of the luminescence as well as the contraction of the defect. [Copyright &y& Elsevier]