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These pictures of the original White source were taken in 1985. The source was an adaptation of the Eaton Nova Freeman source, based on the Bernas source. The goal at the time was to get 50% more boron current. The source occasionally achieved this, but the data varied from machine to machine (another story), and the source was withdrawn shortly after its release. But then it was realized that the source service life had increased by an enormous factor of between 2 and 4, and as a result the source was again released, under the name "Enhanced Source". In some parts of the world the source really took off, particularly in Japan, where the "White Source" name stuck. It has also been sold as an "EFL source", or extended filament life, and became the universal standard, before the present trend to replace it with indirectly heated cathode sources.
The ion source is a hot cathode PIG source running an arc discharge. It is a version of the Bernas source, with the addition of a reflector electrode, or anticathode, at the opposite end of the arc chamber from the filament. An external magnet provides a field running the length of the arc chamber, from left to right in the pictures.
The pigtail filament, biased at -60 to 90V, emits electrons which are electrically attracted to the walls of the arc chamber at local ground. But the magnetic field prevents them from reaching it. Unlike Calutron or Bernas sources, the electrons are also blocked at the opposite end; they are in a Penning trap, and can only reach the anode by scattering off gas molecules, thereby ionizing them. A plume of plasma forms in an intense cylinder from left to right. It is surprisingly uniform, which is one of the advantages of the source we exploited recently at Diamond Semiconductor Group, where we needed to make uniform ribbon beams.
The source keeps most of the ions from eroding the filament, hence its extended life, and is very efficient in its use of the electrons. Recent advantages in indirectly heated cathodes also exploit the Penning trap geometry, and provide longer-lived cathodes.
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Manufacturers told us we couldn't bend tungsten wire of 0.090" into a tight 3/8" diameter loop as the souorce demanded. So we made the tooling and made the filaments ourselves. As manufacturers learnt the trick, we supplied jigs onto which the filament had to fit to pass a go-no go test.
Acknowledgements to August Westner, Bill Reynolds, Michael Kanter, on whose work with the Bernas source this development was based.