Effects of external magnetic filter on behaviors of fast primary electrons in a volume negative ion source.
The relationship between enhancement of hydrogen negative ion H(-), volume production, and behaviors of fast primary electrons is studied theoretically. Trajectories of fast primary electrons are calculated, including collisional effects with hydrogen molecules. Active region of fast electrons depends strongly on the field intensity of the magnetic filter (MF), B(MF), and filament position. Therefore, spatial distributions of ionization and vibrational excitation collision points are also affected with changing B(MF). Although number of vibrational excitation collision points is much smaller than that of ionization collision points due to different mean free path, the relative intensity is varied by changing energy of fast electrons. According to the results and discussions including transport of produced vibrationally excited molecules, for enhancement of H(-) production, it is desired that fast electrons should approach the MF position and move into the downstream region as deep as possible without destruction of H(-) ions. To realize these conditions, good combination between filament position and the intensity of the MF should be required.
Effects of filament positions on the arc discharge characteristics of a negative hydrogen ion source for neutral beam injector
The influence of filament positions on the arc discharge characteristics of a negative hydrogen ion source for a neutral beam injector were studied by simulations and experiments. We have made a simulation code named “PRIMELOC2,” which calculates the orbits of primary electrons emitted from cathode filaments, including collisions with H2 gas molecules filled in the source, to obtain the spatial distribution of ionization points. We applied this code to a large negative hydrogen ion source having an external magnetic filter for LHD-NBI No. 1 (neutral beam injector 1 for a large helical device). As a result of the calculations, we have found that the moving area of emitted primary electrons differs markedly according to the filament positions. Calculation results agreed well with the experimental results of high-power arc discharge and the spatial distribution of plasma parameters obtained by Langmuir probe measurements. By applying PRIMELOC2 to filament–arc ion sources, we can choose appropriate areas in a...
5.63 and 5.80 MeV levels of Ne20; de-excitation branching
Abstract The ratio Г γ /Г for the 5.63 and 5.80 MeV levels of Ne 20 has been determined to be 0.077 (±0.008) and −4 , respectively, by using the C 12 (C 12 , α)Ne 20 reaction and determining the fraction of the events in which the alpha-particle and the Ne 20 recoil are present in coincidence at the kinematically correct angles. In both cases these results in themselves are shown to imply radiative E1 transition (5.63→1.63 and 5.80→0, respectively) probabilities ⪡5 × 10 −5 Weisskopf units. When taken together with the life-time for the 5.63 MeV level measured by Evans et al . values of Г( E1 ) ≲ 5 × 10 −6 and Г α ≈ 6% of the particle estimate are obtained for this state.