26 research outputs found
Optimizing the laser absorption technique for quantification of caesium densities in negative hydrogen ion sources
Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma
The production of negative ions is of significant interest for applications
including mass spectrometry, particle acceleration, material surface
processing, and neutral beam injection for magnetic confinement fusion. Methods
to improve the efficiency of the surface production of negative ions, without
the use of low work function metals, are of interest for mitigating the complex
engineering challenges these materials introduce. In this study we investigate
the production of negative ions by doping diamond with nitrogen. Negatively
biased ( V or V), nitrogen doped micro-crystalline diamond films
are introduced to a low pressure deuterium plasma (helicon source operated in
capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions
(NIEDFs) are measured via mass spectrometry with respect to the surface
temperature (30C to 750C) and dopant concentration. The
results suggest that nitrogen doping has little influence on the yield when the
sample is biased at V, but when a relatively small bias voltage of
V is applied the yield is increased by a factor of 2 above that of un-doped
diamond when its temperature reaches 550C. The doping of diamond with
nitrogen is a new method for controlling the surface production of negative
ions, which continues to be of significant interest for a wide variety of
practical applications
Characteristics of a high-power RF source of negative hydrogen ions for neutral beam injection into controlled fusion devices
Optimization of Cs Deposition in the 1/3 Scale Hydrogen Negative Ion Source for LHD-NBI System
"A compact cesium deposition system was used for direct deposition of cesim atoms and ion onto the inner surface of the 1/3 scale Hydrogen Negative Ion Source for the LHD-NBI system. A small, well defined amount of cesium deposition in the range of 3-200 mg was tested. Negative ion extraction and acceleration were carried out both in the pure hydrogen operation mode and in the cesium mode. Single Cs deposition of 3-30 mg to the plasma chamber have produced temporary 2-5 times increases of H- yield, but the yield was decreased within several discharge pulses to the previous steady-state value. Two consecutive 30 mg depositions done within a 3-5 hours/ 60 shot interval, produced a similar temporary increase of H- beam, but reached a larger H-yielad steady-state value. Deposition of arger 0.1-0.2 g Cs portions with a 20-120 hours/150-270 shot interval improved the H-yield for a long (2-5 days) period of operation. Directed depositions of Cs to the various walls of the plasma chamber showed approximately the same H- increase. Deposition of 0.13 g Cs to a surface polluted by a water leak, produced a temporary increase, and an H- steady-state level similar to that from a single 30 mg cesium deposition. Deposition of 0.1 g with a cesium plasma produced one half the H-yield obtained by deposition of the same amount of cesium atoms. A higher steady-state H- current value and a smaller rate of H- yield decrease was recorded during the 8 filaments discharge operation, as compared to the 12 filaments operation at the same discharge power.