Gas discharge ion source. I. Duoplasmatron.
The effects of the plasma expansion cup on the operation of a duoplasmatron ion source have been investigated by measuring the total ion current and the distributions of the ion energy, mass, and current density. A copper expansion cup did not affect the magnetic field near the anode of the ion source and consequently the ion current density distribution was sharply peaked near the center of the cup. Ion energy distributions were approximately symmetrical about anode potential. The dominant ionic species were D(+) (3) and D(+) at low and high arc currents, respectively. Changes in the electrical potential of the copper cup with respect to the anode produced negligible changes in the above data. A mild steel plasma expansion cup caused the magnetic field to diverge and intercept the cup walls, resulting in ion current density distributions that were flatter and more amenable to focusing than the ones with the copper cup. With the steel cup at anode potential, the ion mass distribution was similar to that from the copper cup; however, the ion energy distribution was asymmetrical about the anode potential with a peak about 10-20 V above anode potential. The total ion current from this mode of operation was about one-third the value from the copper cup. If the steel cup assumed floating potential, about 50 V below anode potential, the total current increased to the level observed from the copper cup and the ion energy distribution was similar to that observed with the copper cup but the current density distribution was much flatter than that of the copper cup. The ion mass distribution was 60%-70% atomic ions over the entire arc current range investigated. Based on these data, a modified plasma expansion cup was designed with tapered steel walls lined with a boron nitride insert. The overall performance of the duoplasmatron ion source with this cup was superior to any of the previous three modes of operation. The improved design uses a molybdenum anode insert which is far superior to copper in regard to erosion over extended operating times. A total beam current of 200 mA was produced at an arc current of 24 A.
Energy distributions of mass-selected ions from the plasma of a pulsed vacuum arc
Abstract Energy and angular distributions of mass-selected ions from the plasma of a vacuum arc of 5–6 μsec duration have been measured using a cylindrical electrostatic energy analyzer in tandem with a quadrupole mass filter. The arc electrodes were Kovar separated by an alumina ceramic insulator, with a thin strip of vanadium deposited over the anode and the insulator surface between the electrodes. Energy distributions have been measured for V +1 , V +2 , and V +3 from the vanadium film; O +1 , O +2 , Al +2 , and Al +3 from the insulator; and C +1 and C +2 from carbonaceous contaminants. The significant features of the energy distributions are the existence of a low-energy cutoff, the presence of a single peak having a characteristic energy position and width, and the presence of a high-energy component with ion energies per unit charge greater than the total arc voltage. The angular distributions indicate that no directional energy discrimination was introduced by performing the energy measurements in the forward direction.
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.