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Description
Accelerators around the world employ non-evaporable getter (NEG) coatings in their beamlines to achieve the ultra-low pressures required for operation. Compared with standard vacuum chamber materials such as steel or copper, NEG coatings have lower gas desorption, lower electron clouding effects, and additionally provide a distributed pumping effect, allowing very small apertures for the beamline pipes, allowing more efficient control of the beam.
However, compared with copper, NEG coatings have a lower conductivity, which can cause resistive wavefields to form, causing loss in beam energy. To reduce this, many NEG coating thickness may be reduced, but with a sacrifice of the pumping properties. Alternatively, electrically conductive materials (e.g. Ag or Cu) may be introduced into the NEG coating during deposition, which may reduce the resistivity of the NEG coating.
A study was completed at Daresbury laboratory, in which several samples of different composition, and different contents of Ag, were deposited onto tubular vessels. The pumping properties and resistivity of each tube was measured to determine what the best compromise between the two properties can be achieved by varying coating composition. Some additional testing on coating thickness was also completed, to compare with finding of previous studies.
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