Increased ion source life for Varian´s kestrel implanter

In an effort to extend the longevity of the Bernas source on Varian´s MeV implanters, the effect on source life of increasing the diameter of the extraction aperture was studied. For a given beam current, plasma density is inversely proportional to the aperture area. Since source life is inversely proportional to plasma density, it should, then increase linearly with the aperture area. Two diameters were investigated: one with 40% more area, and one with twice the area. Extraction was modeled using KOBRA, and then tested. An observation made from tests indicated that the gas flow required to maintain a stable arc was found to increase precipitously with the larger aperture; therefore attention was restricted to the first one. Results from the tests also showed that the required arc power to produce spec beam was reduced by about 40%, as expected, and transmission through the Tandetron was unaffected. A series of source life tests were then conducted, with a 50/50 mix of phosphine and boron. Results showed the expected 40% increase. Finally some of the tests were performed with a tungsten arc chamber to evaluate tungsten filament re-growth (“halogen effect”) on source life